From patchwork Tue Mar 30 20:57:45 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 12173719 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-23.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5F136C433DB for ; Tue, 30 Mar 2021 20:58:27 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 9BE17619C5 for ; Tue, 30 Mar 2021 20:58:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9BE17619C5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-21085-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 5228 invoked by uid 550); 30 Mar 2021 20:58:07 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 5156 invoked from network); 30 Mar 2021 20:58:06 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=9ijlYcKqhmRnIjh3GfaZu6VzSGgGwccaBk76YZfh88U=; b=FE7kn9uccaNwZUZ65DKIqMMeCF4L8T5uHj+6rAX1M16+hIAiROMPCoW0ANbpyvkauA zNm2OopXkQ6LAOsRPbIK640iKsOLSDOOggNsbZdq6eYIsT34pwdagUeVUvG7xjxhyCBj zo84r5YxnuOMKbimr0OM8w19pz/qkGBGzGeOI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=9ijlYcKqhmRnIjh3GfaZu6VzSGgGwccaBk76YZfh88U=; b=R2NSFVj/gz/Isd6Z353hIdYBdiYTx9KrY76INs8wuj5bem0TdzlM/NVR9x0/geW6oF KK7Hg610v/bs1ZOIxsan3NT1aLkG8FACa1fkV2u1DBHoeGm4xOiGlwZUXlY3lnQWYVN7 JEnszosurfkaJYwhkugSb5j3NJoZkHKtCJtKnepSzv+CZSqzu80ostrF+94zE+1jD32m zBfMAIfmsYfy/gC7BQAGTfuxIL72YvxAXVFoiombxnEt4E3Y3gTU9ZuA565vtEimU+2H Qq7WBMzQiKgZhJ8XOpJ4mjD6muWPDNfYAHEw6sE2zJweenu/Y+gLYIZ/dNeTm7CjGzr6 qTHQ== X-Gm-Message-State: AOAM531AAOSMD6SYqacwGV9eGhGO8GFkGzu6e74do8cxjlZxUouuJR97 EZCkCWKa8m1UrAurwuHF+Cuydg== X-Google-Smtp-Source: ABdhPJxKiSYrHQGcEilxb2Xm7psWt7RDOXuAoFkC/UflndAY9YjgBstIUNwwje4/jGjMrGhbk14LkA== X-Received: by 2002:a17:90b:38f:: with SMTP id ga15mr170436pjb.149.1617137874107; Tue, 30 Mar 2021 13:57:54 -0700 (PDT) From: Kees Cook To: Thomas Gleixner Cc: Kees Cook , Peter Zijlstra , Elena Reshetova , x86@kernel.org, Andy Lutomirski , Catalin Marinas , Will Deacon , Mark Rutland , Alexander Potapenko , Alexander Popov , Ard Biesheuvel , Jann Horn , Vlastimil Babka , David Hildenbrand , Mike Rapoport , Andrew Morton , Jonathan Corbet , Randy Dunlap , kernel-hardening@lists.openwall.com, linux-hardening@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v8 1/6] jump_label: Provide CONFIG-driven build state defaults Date: Tue, 30 Mar 2021 13:57:45 -0700 Message-Id: <20210330205750.428816-2-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210330205750.428816-1-keescook@chromium.org> References: <20210330205750.428816-1-keescook@chromium.org> MIME-Version: 1.0 X-Patch-Hashes: v=1; h=sha256; g=aa54c44d1d71b9550d6015efc734f667917094a1; i=Vishx6UyAXwYzcnoSyP+eBB3iQyx+/i5smsbQfc0cnA=; m=vc4sSYlf+uaSlLSFP5TpbQv56VaSRpBLpRuMltXaB4Q=; p=mNH2Bo/K9vrGz9sBtTDV8UFO0eJ8yv8BbR/DeIaO1es= X-Patch-Sig: m=pgp; i=keescook@chromium.org; s=0x0x8972F4DFDC6DC026; b=iQIzBAABCgAdFiEEpcP2jyKd1g9yPm4TiXL039xtwCYFAmBjkMwACgkQiXL039xtwCaWexAAp34 ok/GqKys22n/+Xt+9QrE/sBFj+uvgYjI14mqH/xkZoouYd5+myYJn0h/B8R83n48nwB7KdYtukzVv nSela//6I+ohCNhjgEt1TmUc81qTISl5q5mxbq/+IAPNVqlXEYCpTcSFkBbr5tbXOoOrbkI87vrja az8w6YyJGWbCBm/PpNK/FqvgxnWKMmJbomwDiBeWSgEfJUSD/M/r6PV1RhbK2mt7AniDqOPJ/oRG0 VB6GcbfW106hXfwKjmeqoce8yTv7YrC4mYL5sKA0yV/H62mmU9vkUtd+/0x07Cg1iXFAbg3bkDu/i hQkdH1ZBkjnjcWQJ6pvYBfHR+5Fblp8ibFwpPJc/hJmGkzxTde5pAlM3s4FMdtv++qD7bvL2tdXIS kzkw4HJRrjKMET9L3sAWvlSZgUTAip8wslmfIZUVea7HUy5ypoFIvSxHL5BNOGiTBp0zWwvXAzNt1 PTrOAP9fZKIsGI0Nj6laG2wpUdzjTpYcjfNxIPtygIIqheWGFwHwPYpWV0g8700cR/heR7qoBa0zt nrQX1WU7AUkaYROLg1QVWr13bMVlZZuDsSPfvsu3yo8alzHhY8xaryuKCwuTzY8ResHzU6XIqkmJb J1b8qCZ973eAn1T3KbVOk18YcqsShZ8C4SwIbyGOuesFrhes7bPZf/GqTx2MNcoU= As shown in jump_label.h[1], choosing the initial state of static branches changes the assembly layout. If the condition is expected to be likely it's inline, and if unlikely it is out of line via a jump. A few places in the kernel use (or could be using) a CONFIG to choose the default state, which would give a small performance benefit to their compile-time declared default. Provide the infrastructure to do this. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/jump_label.h?h=v5.11#n398 Acked-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/lkml/20200324220641.GT2452@worktop.programming.kicks-ass.net/ Signed-off-by: Kees Cook --- include/linux/jump_label.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h index d92691262f51..05f5554d860f 100644 --- a/include/linux/jump_label.h +++ b/include/linux/jump_label.h @@ -382,6 +382,21 @@ struct static_key_false { [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \ } +#define _DEFINE_STATIC_KEY_1(name) DEFINE_STATIC_KEY_TRUE(name) +#define _DEFINE_STATIC_KEY_0(name) DEFINE_STATIC_KEY_FALSE(name) +#define DEFINE_STATIC_KEY_MAYBE(cfg, name) \ + __PASTE(_DEFINE_STATIC_KEY_, IS_ENABLED(cfg))(name) + +#define _DEFINE_STATIC_KEY_RO_1(name) DEFINE_STATIC_KEY_TRUE_RO(name) +#define _DEFINE_STATIC_KEY_RO_0(name) DEFINE_STATIC_KEY_FALSE_RO(name) +#define DEFINE_STATIC_KEY_MAYBE_RO(cfg, name) \ + __PASTE(_DEFINE_STATIC_KEY_RO_, IS_ENABLED(cfg))(name) + +#define _DECLARE_STATIC_KEY_1(name) DECLARE_STATIC_KEY_TRUE(name) +#define _DECLARE_STATIC_KEY_0(name) DECLARE_STATIC_KEY_FALSE(name) +#define DECLARE_STATIC_KEY_MAYBE(cfg, name) \ + __PASTE(_DECLARE_STATIC_KEY_, IS_ENABLED(cfg))(name) + extern bool ____wrong_branch_error(void); #define static_key_enabled(x) \ @@ -482,6 +497,10 @@ extern bool ____wrong_branch_error(void); #endif /* CONFIG_JUMP_LABEL */ +#define static_branch_maybe(config, x) \ + (IS_ENABLED(config) ? static_branch_likely(x) \ + : static_branch_unlikely(x)) + /* * Advanced usage; refcount, branch is enabled when: count != 0 */ From patchwork Tue Mar 30 20:57:46 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 12173721 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0B812C433E5 for ; Tue, 30 Mar 2021 20:58:35 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 2878A6199A for ; Tue, 30 Mar 2021 20:58:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2878A6199A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-21086-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 5273 invoked by uid 550); 30 Mar 2021 20:58:08 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 5154 invoked from network); 30 Mar 2021 20:58:06 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=UG6lpZSAG8t+NfdJici9YkMGF34rxaYTMGPEmVDXXFs=; b=nAtL0yLEpjO2guyFAnk1UK8RCNVE817hSH2Q172t9upN0Y9DcHi4VPdazL0wXZjLfd xlHHSMBZWyFEw7jxyLinGl0JaLbvCqzWK4kVm5P+6y5xzoKJRTbfmuOnH8+1yQshwVQ8 emm1ECwHM5YtpWRAoVYZwoNNTFLms6VvWOqLU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=UG6lpZSAG8t+NfdJici9YkMGF34rxaYTMGPEmVDXXFs=; b=CZ5b/Wuc391ZgPusxnKyuEL3mXTjqdCqHjyAqPncjdjO8pWnlSS0RuaxhOZMY3qTlg h3RK9TOH86XeFKZhj0++J+88B5WIQZwiD+HOnHjKP+OksuA7o/QaQhKPl2ceMcnApZ3u +xNeNefq8Y5Ycsu1S6HFiZnYU243W/PgoEjmq8RJyR3qJJv6pu0NdGdZAmh2TOWMjXib Frc+Ia2N0RdwgL6ijwjwX6QNoBJgnUM7pYDKsJ95N0+aBlavPWI8aWhuGJEN1oldXhfS 6D5HN/2X5/iC4se0pQEwaCR7XsuaPMRhFqwFlaygkMnt56Gw38w2G6Zq8b0NoAqklZwC WMbA== X-Gm-Message-State: AOAM531IIJfmXgPukcnCietGBzRypl7ECO9JYbD1Z7TkovDGduRhIzwQ wZDrON1Su//o/SYESBuuRpLzoQ== X-Google-Smtp-Source: ABdhPJz3LXv4eDOhFhF6lIjzHku5IEzcEABiR69AQC5cXMNAv6qJ/s1o3KIyukaQCofHm60NmmHgeA== X-Received: by 2002:a62:8fcd:0:b029:218:461:2279 with SMTP id n196-20020a628fcd0000b029021804612279mr31460592pfd.43.1617137873522; Tue, 30 Mar 2021 13:57:53 -0700 (PDT) From: Kees Cook To: Thomas Gleixner Cc: Kees Cook , Alexander Potapenko , Vlastimil Babka , Elena Reshetova , x86@kernel.org, Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Mark Rutland , Alexander Popov , Ard Biesheuvel , Jann Horn , David Hildenbrand , Mike Rapoport , Andrew Morton , Jonathan Corbet , Randy Dunlap , kernel-hardening@lists.openwall.com, linux-hardening@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v8 2/6] init_on_alloc: Optimize static branches Date: Tue, 30 Mar 2021 13:57:46 -0700 Message-Id: <20210330205750.428816-3-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210330205750.428816-1-keescook@chromium.org> References: <20210330205750.428816-1-keescook@chromium.org> MIME-Version: 1.0 X-Patch-Hashes: v=1; h=sha256; g=2f4b59272e09d0180c87e3d8378d95ea375990ec; i=7VrM8Pzr5MGi8vAaDOW4xeiDtVYbjHgJsdLlT/sxDXE=; m=OLLKLAHsfNT1d7+pflxMGJuAvSt8GZaetKIXzfk0ilc=; p=cKq4RSNZSRZ+ASTC07w37jURMQB1hxGsdgqU07adDH0= X-Patch-Sig: m=pgp; i=keescook@chromium.org; s=0x0x8972F4DFDC6DC026; b=iQIzBAABCgAdFiEEpcP2jyKd1g9yPm4TiXL039xtwCYFAmBjkMwACgkQiXL039xtwCZc3RAAneZ W9nsrEVAJu/2EM9W3eP/wNa9JCKIEGXsfdWDWQPPeCbpGDVnJgSVyjiCWUFr4tej6kSR2JcjNkDtk RamMPpNcmIBTAEQZCMJvmrtcKW1IDd/OGeQba5IsPM2+nzcu7TIihfbnaOaO007hiw5q0lN0dy6Vz INq699xnV4EDdLtYeikcR+yHjgF9BrTpVkRdUUD05riIM5MKdp1bCEELMVGvRNofeTRfnTwGW+P08 L8DpSkB+4LmS285BqK0bLDrBFkIlT32vvQmNur8jFep9Yddh2uApO3GfmkatNKXr2pZhthk9ylXAt oLYfDTHsftsgfeBeeCgYWbz52VxjzKw2QlqYy98p2kmLbSWjhZs+mnMvjUfTsHk3tE8pULROEkkxQ EYBq2yGgZCxW/DplktGsnIw2+IuXr5ZVmszBhCU7fjdfnuUpGieeboPgZ3bsyFyLCg5COu0WaMU2k NqhLH42LJzP9w7bvvdccxuPX4DwZjsue4iDmmZgYnWCq20wHcbjVquMuhe5+Z4iMSYCe12rKUT8mh qYDodBX6u5xZgbfJp+x144gtPE89shG9i69yAXKWgC/kRl/en7wYjeg0utnlpYkc+Vg0Oe3I5Jkfs TmEtbMUzu1eA1785dXZn5CS1UZL6KK1W57w5r0f3u7y/IwvVYp1i1NAnZT/lq1BQ= The state of CONFIG_INIT_ON_ALLOC_DEFAULT_ON (and ...ON_FREE...) did not change the assembly ordering of the static branches: they were always out of line. Use the new jump_label macros to check the CONFIG settings to default to the "expected" state, which slightly optimizes the resulting assembly code. Reviewed-by: Alexander Potapenko Link: https://lore.kernel.org/lkml/CAG_fn=X0DVwqLaHJTO6Jw7TGcMSm77GKHinrd0m_6y0SzWOrFA@mail.gmail.com/ Acked-by: Vlastimil Babka Link: https://lore.kernel.org/lkml/5d626b9b-5355-be94-e8e2-1be47f880f30@suse.cz Signed-off-by: Kees Cook --- include/linux/mm.h | 10 ++++++---- mm/page_alloc.c | 4 ++-- mm/slab.h | 6 ++++-- 3 files changed, 12 insertions(+), 8 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 77e64e3eac80..2ccd856ac0d1 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2871,18 +2871,20 @@ static inline void kernel_poison_pages(struct page *page, int numpages) { } static inline void kernel_unpoison_pages(struct page *page, int numpages) { } #endif -DECLARE_STATIC_KEY_FALSE(init_on_alloc); +DECLARE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, init_on_alloc); static inline bool want_init_on_alloc(gfp_t flags) { - if (static_branch_unlikely(&init_on_alloc)) + if (static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, + &init_on_alloc)) return true; return flags & __GFP_ZERO; } -DECLARE_STATIC_KEY_FALSE(init_on_free); +DECLARE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_FREE_DEFAULT_ON, init_on_free); static inline bool want_init_on_free(void) { - return static_branch_unlikely(&init_on_free); + return static_branch_maybe(CONFIG_INIT_ON_FREE_DEFAULT_ON, + &init_on_free); } extern bool _debug_pagealloc_enabled_early; diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3e4b29ee2b1e..267c04b8911d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -167,10 +167,10 @@ unsigned long totalcma_pages __read_mostly; int percpu_pagelist_fraction; gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK; -DEFINE_STATIC_KEY_FALSE(init_on_alloc); +DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, init_on_alloc); EXPORT_SYMBOL(init_on_alloc); -DEFINE_STATIC_KEY_FALSE(init_on_free); +DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_FREE_DEFAULT_ON, init_on_free); EXPORT_SYMBOL(init_on_free); static bool _init_on_alloc_enabled_early __read_mostly diff --git a/mm/slab.h b/mm/slab.h index 076582f58f68..774c7221efdc 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -601,7 +601,8 @@ static inline void cache_random_seq_destroy(struct kmem_cache *cachep) { } static inline bool slab_want_init_on_alloc(gfp_t flags, struct kmem_cache *c) { - if (static_branch_unlikely(&init_on_alloc)) { + if (static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, + &init_on_alloc)) { if (c->ctor) return false; if (c->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)) @@ -613,7 +614,8 @@ static inline bool slab_want_init_on_alloc(gfp_t flags, struct kmem_cache *c) static inline bool slab_want_init_on_free(struct kmem_cache *c) { - if (static_branch_unlikely(&init_on_free)) + if (static_branch_maybe(CONFIG_INIT_ON_FREE_DEFAULT_ON, + &init_on_free)) return !(c->ctor || (c->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON))); return false; From patchwork Tue Mar 30 20:57:47 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 12173727 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F3209C433C1 for ; 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Tue, 30 Mar 2021 13:57:55 -0700 (PDT) From: Kees Cook To: Thomas Gleixner Cc: Kees Cook , Elena Reshetova , x86@kernel.org, Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Mark Rutland , Alexander Potapenko , Alexander Popov , Ard Biesheuvel , Jann Horn , Vlastimil Babka , David Hildenbrand , Mike Rapoport , Andrew Morton , Jonathan Corbet , Randy Dunlap , kernel-hardening@lists.openwall.com, linux-hardening@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v8 3/6] stack: Optionally randomize kernel stack offset each syscall Date: Tue, 30 Mar 2021 13:57:47 -0700 Message-Id: <20210330205750.428816-4-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210330205750.428816-1-keescook@chromium.org> References: <20210330205750.428816-1-keescook@chromium.org> MIME-Version: 1.0 X-Patch-Hashes: v=1; h=sha256; g=2603f6854c520ce7239e473b49572b2a8d918ecd; i=R0fcIKmEUh8zot7Dpk8JcJdIeXVfXkVsg5oQI7Df8iY=; m=PHRmEj7s2c5znQ32d6PHiKjZ1zRrKOiokm7KXcpFb34=; p=1bzIQ4s8vyUlpPOqai5LPd/UVsRKDjzH5IawjFmzLPE= X-Patch-Sig: m=pgp; i=keescook@chromium.org; s=0x0x8972F4DFDC6DC026; b=iQIzBAABCgAdFiEEpcP2jyKd1g9yPm4TiXL039xtwCYFAmBjkMwACgkQiXL039xtwCZT2w//X78 EO/7SJdUinoKC0RJWZz77Y8+4cwyBZkottoxUo79lEZTlBOZrVghLoMXXMwU7OkXu3r9npj9Ms/AX GxoA06QPh1ul5Vsh/8yGB7FytbYhHuz0+fVkYlXYEYnUHyD+UcLPjKnSJqR+8NPnyHQ/cb9KtKGOC A4iC0gYjk4gAD6e5d33lSazKkHQRbC02y58od7wPFPuGUDKeRunSwJaVyBXJQaojf65pT12nWGQN/ AD7kbxOe6jWd8O+TnM7A/kqg2eRcLexg/wRR7hpSRTgg7MwAqZ4xTrnwleJHvDGMqdDN4jy4b3qev uCIKquKbRa9SbuO8w/6Scg0YLafYP8h6ueuiMT8DlLUn6yGOZTrCyuyITjmFMiazwydn78WttU05S oee40lhpZR4f/BU6ea+VVSH9B6NYQp1ZV30mKe6eX9RM2nsmI/FjJbk7Z6+8zhl97vYriDY69aNQx RuIonsJQ7HwZmgnIVBBJFjw3gSNFbJGaokEu13wA+i8Nybhb5jo/lXUVhFurpcu5YJhdstyrmOo0V 8XXh0VeUOy6fmPeffxglHY6+kpwAwNfRX32OMUk8Bq+axGSSq5H/nXvBo2r+qS4RtHQvjyZ9UAihu n+0UnHR/OkFZfK2/8cn5oMN6quQCnypI2aWpm2/f6wLwjIpgEJEyOAo8EPnarT60= This provides the ability for architectures to enable kernel stack base address offset randomization. This feature is controlled by the boot param "randomize_kstack_offset=on/off", with its default value set by CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. This feature is based on the original idea from the last public release of PaX's RANDKSTACK feature: https://pax.grsecurity.net/docs/randkstack.txt All the credit for the original idea goes to the PaX team. Note that the design and implementation of this upstream randomize_kstack_offset feature differs greatly from the RANDKSTACK feature (see below). Reasoning for the feature: This feature aims to make harder the various stack-based attacks that rely on deterministic stack structure. We have had many such attacks in past (just to name few): https://jon.oberheide.org/files/infiltrate12-thestackisback.pdf https://jon.oberheide.org/files/stackjacking-infiltrate11.pdf https://googleprojectzero.blogspot.com/2016/06/exploiting-recursion-in-linux-kernel_20.html As Linux kernel stack protections have been constantly improving (vmap-based stack allocation with guard pages, removal of thread_info, STACKLEAK), attackers have had to find new ways for their exploits to work. They have done so, continuing to rely on the kernel's stack determinism, in situations where VMAP_STACK and THREAD_INFO_IN_TASK_STRUCT were not relevant. For example, the following recent attacks would have been hampered if the stack offset was non-deterministic between syscalls: https://repositorio-aberto.up.pt/bitstream/10216/125357/2/374717.pdf (page 70: targeting the pt_regs copy with linear stack overflow) https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html (leaked stack address from one syscall as a target during next syscall) The main idea is that since the stack offset is randomized on each system call, it is harder for an attack to reliably land in any particular place on the thread stack, even with address exposures, as the stack base will change on the next syscall. Also, since randomization is performed after placing pt_regs, the ptrace-based approach[1] to discover the randomized offset during a long-running syscall should not be possible. Design description: During most of the kernel's execution, it runs on the "thread stack", which is pretty deterministic in its structure: it is fixed in size, and on every entry from userspace to kernel on a syscall the thread stack starts construction from an address fetched from the per-cpu cpu_current_top_of_stack variable. The first element to be pushed to the thread stack is the pt_regs struct that stores all required CPU registers and syscall parameters. Finally the specific syscall function is called, with the stack being used as the kernel executes the resulting request. The goal of randomize_kstack_offset feature is to add a random offset after the pt_regs has been pushed to the stack and before the rest of the thread stack is used during the syscall processing, and to change it every time a process issues a syscall. The source of randomness is currently architecture-defined (but x86 is using the low byte of rdtsc()). Future improvements for different entropy sources is possible, but out of scope for this patch. Further more, to add more unpredictability, new offsets are chosen at the end of syscalls (the timing of which should be less easy to measure from userspace than at syscall entry time), and stored in a per-CPU variable, so that the life of the value does not stay explicitly tied to a single task. As suggested by Andy Lutomirski, the offset is added using alloca() and an empty asm() statement with an output constraint, since it avoids changes to assembly syscall entry code, to the unwinder, and provides correct stack alignment as defined by the compiler. In order to make this available by default with zero performance impact for those that don't want it, it is boot-time selectable with static branches. This way, if the overhead is not wanted, it can just be left turned off with no performance impact. The generated assembly for x86_64 with GCC looks like this: ... ffffffff81003977: 65 8b 05 02 ea 00 7f mov %gs:0x7f00ea02(%rip),%eax # 12380 ffffffff8100397e: 25 ff 03 00 00 and $0x3ff,%eax ffffffff81003983: 48 83 c0 0f add $0xf,%rax ffffffff81003987: 25 f8 07 00 00 and $0x7f8,%eax ffffffff8100398c: 48 29 c4 sub %rax,%rsp ffffffff8100398f: 48 8d 44 24 0f lea 0xf(%rsp),%rax ffffffff81003994: 48 83 e0 f0 and $0xfffffffffffffff0,%rax ... As a result of the above stack alignment, this patch introduces about 5 bits of randomness after pt_regs is spilled to the thread stack on x86_64, and 6 bits on x86_32 (since its has 1 fewer bit required for stack alignment). The amount of entropy could be adjusted based on how much of the stack space we wish to trade for security. My measure of syscall performance overhead (on x86_64): lmbench: /usr/lib/lmbench/bin/x86_64-linux-gnu/lat_syscall -N 10000 null randomize_kstack_offset=y Simple syscall: 0.7082 microseconds randomize_kstack_offset=n Simple syscall: 0.7016 microseconds So, roughly 0.9% overhead growth for a no-op syscall, which is very manageable. And for people that don't want this, it's off by default. There are two gotchas with using the alloca() trick. First, compilers that have Stack Clash protection (-fstack-clash-protection) enabled by default (e.g. Ubuntu[3]) add pagesize stack probes to any dynamic stack allocations. While the randomization offset is always less than a page, the resulting assembly would still contain (unreachable!) probing routines, bloating the resulting assembly. To avoid this, -fno-stack-clash-protection is unconditionally added to the kernel Makefile since this is the only dynamic stack allocation in the kernel (now that VLAs have been removed) and it is provably safe from Stack Clash style attacks. The second gotcha with alloca() is a negative interaction with -fstack-protector*, in that it sees the alloca() as an array allocation, which triggers the unconditional addition of the stack canary function pre/post-amble which slows down syscalls regardless of the static branch. In order to avoid adding this unneeded check and its associated performance impact, architectures need to carefully remove uses of -fstack-protector-strong (or -fstack-protector) in the compilation units that use the add_random_kstack() macro and to audit the resulting stack mitigation coverage (to make sure no desired coverage disappears). No change is visible for this on x86 because the stack protector is already unconditionally disabled for the compilation unit, but the change is required on arm64. There is, unfortunately, no attribute that can be used to disable stack protector for specific functions. Comparison to PaX RANDKSTACK feature: The RANDKSTACK feature randomizes the location of the stack start (cpu_current_top_of_stack), i.e. including the location of pt_regs structure itself on the stack. Initially this patch followed the same approach, but during the recent discussions[2], it has been determined to be of a little value since, if ptrace functionality is available for an attacker, they can use PTRACE_PEEKUSR/PTRACE_POKEUSR to read/write different offsets in the pt_regs struct, observe the cache behavior of the pt_regs accesses, and figure out the random stack offset. Another difference is that the random offset is stored in a per-cpu variable, rather than having it be per-thread. As a result, these implementations differ a fair bit in their implementation details and results, though obviously the intent is similar. [1] https://lore.kernel.org/kernel-hardening/2236FBA76BA1254E88B949DDB74E612BA4BC57C1@IRSMSX102.ger.corp.intel.com/ [2] https://lore.kernel.org/kernel-hardening/20190329081358.30497-1-elena.reshetova@intel.com/ [3] https://lists.ubuntu.com/archives/ubuntu-devel/2019-June/040741.html Co-developed-by: Elena Reshetova Signed-off-by: Elena Reshetova Link: https://lore.kernel.org/r/20190415060918.3766-1-elena.reshetova@intel.com Signed-off-by: Kees Cook Reviewed-by: Thomas Gleixner --- .../admin-guide/kernel-parameters.txt | 11 ++++ Makefile | 4 ++ arch/Kconfig | 23 ++++++++ include/linux/randomize_kstack.h | 55 +++++++++++++++++++ init/main.c | 23 ++++++++ 5 files changed, 116 insertions(+) create mode 100644 include/linux/randomize_kstack.h diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 04545725f187..bee8644a192e 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4061,6 +4061,17 @@ fully seed the kernel's CRNG. Default is controlled by CONFIG_RANDOM_TRUST_CPU. + randomize_kstack_offset= + [KNL] Enable or disable kernel stack offset + randomization, which provides roughly 5 bits of + entropy, frustrating memory corruption attacks + that depend on stack address determinism or + cross-syscall address exposures. This is only + available on architectures that have defined + CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. + Format: (1/Y/y=enable, 0/N/n=disable) + Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. + ras=option[,option,...] [KNL] RAS-specific options cec_disable [X86] diff --git a/Makefile b/Makefile index 31dcdb3d61fa..8a959a264588 100644 --- a/Makefile +++ b/Makefile @@ -811,6 +811,10 @@ KBUILD_CFLAGS += -ftrivial-auto-var-init=zero KBUILD_CFLAGS += -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang endif +# While VLAs have been removed, GCC produces unreachable stack probes +# for the randomize_kstack_offset feature. Disable it for all compilers. +KBUILD_CFLAGS += $(call cc-option, -fno-stack-clash-protection) + DEBUG_CFLAGS := # Workaround for GCC versions < 5.0 diff --git a/arch/Kconfig b/arch/Kconfig index 2bb30673d8e6..4fe6b047fcbc 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -1055,6 +1055,29 @@ config VMAP_STACK backing virtual mappings with real shadow memory, and KASAN_VMALLOC must be enabled. +config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET + def_bool n + help + An arch should select this symbol if it can support kernel stack + offset randomization with calls to add_random_kstack_offset() + during syscall entry and choose_random_kstack_offset() during + syscall exit. Careful removal of -fstack-protector-strong and + -fstack-protector should also be applied to the entry code and + closely examined, as the artificial stack bump looks like an array + to the compiler, so it will attempt to add canary checks regardless + of the static branch state. + +config RANDOMIZE_KSTACK_OFFSET_DEFAULT + bool "Randomize kernel stack offset on syscall entry" + depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET + help + The kernel stack offset can be randomized (after pt_regs) by + roughly 5 bits of entropy, frustrating memory corruption + attacks that depend on stack address determinism or + cross-syscall address exposures. This feature is controlled + by kernel boot param "randomize_kstack_offset=on/off", and this + config chooses the default boot state. + config ARCH_OPTIONAL_KERNEL_RWX def_bool n diff --git a/include/linux/randomize_kstack.h b/include/linux/randomize_kstack.h new file mode 100644 index 000000000000..351520803006 --- /dev/null +++ b/include/linux/randomize_kstack.h @@ -0,0 +1,55 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +#ifndef _LINUX_RANDOMIZE_KSTACK_H +#define _LINUX_RANDOMIZE_KSTACK_H + +#include +#include +#include + +DECLARE_STATIC_KEY_MAYBE(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, + randomize_kstack_offset); +DECLARE_PER_CPU(u32, kstack_offset); + +/* + * Do not use this anywhere else in the kernel. This is used here because + * it provides an arch-agnostic way to grow the stack with correct + * alignment. Also, since this use is being explicitly masked to a max of + * 10 bits, stack-clash style attacks are unlikely. For more details see + * "VLAs" in Documentation/process/deprecated.rst + * The asm statement is designed to convince the compiler to keep the + * allocation around even after "ptr" goes out of scope. + */ +void *__builtin_alloca(size_t size); +/* + * Use, at most, 10 bits of entropy. We explicitly cap this to keep the + * "VLA" from being unbounded (see above). 10 bits leaves enough room for + * per-arch offset masks to reduce entropy (by removing higher bits, since + * high entropy may overly constrain usable stack space), and for + * compiler/arch-specific stack alignment to remove the lower bits. + */ +#define KSTACK_OFFSET_MAX(x) ((x) & 0x3FF) + +/* + * These macros must be used during syscall entry when interrupts and + * preempt are disabled, and after user registers have been stored to + * the stack. + */ +#define add_random_kstack_offset() do { \ + if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \ + &randomize_kstack_offset)) { \ + u32 offset = __this_cpu_read(kstack_offset); \ + u8 *ptr = __builtin_alloca(KSTACK_OFFSET_MAX(offset)); \ + asm volatile("" : "=m"(*ptr) :: "memory"); \ + } \ +} while (0) + +#define choose_random_kstack_offset(rand) do { \ + if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \ + &randomize_kstack_offset)) { \ + u32 offset = __this_cpu_read(kstack_offset); \ + offset ^= (rand); \ + __this_cpu_write(kstack_offset, offset); \ + } \ +} while (0) + +#endif diff --git a/init/main.c b/init/main.c index 53b278845b88..f498aac26e8c 100644 --- a/init/main.c +++ b/init/main.c @@ -844,6 +844,29 @@ static void __init mm_init(void) pti_init(); } +#ifdef CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET +DEFINE_STATIC_KEY_MAYBE_RO(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, + randomize_kstack_offset); +DEFINE_PER_CPU(u32, kstack_offset); + +static int __init early_randomize_kstack_offset(char *buf) +{ + int ret; + bool bool_result; + + ret = kstrtobool(buf, &bool_result); + if (ret) + return ret; + + if (bool_result) + static_branch_enable(&randomize_kstack_offset); + else + static_branch_disable(&randomize_kstack_offset); + return 0; +} +early_param("randomize_kstack_offset", early_randomize_kstack_offset); +#endif + void __init __weak arch_call_rest_init(void) { rest_init(); From patchwork Tue Mar 30 20:57:48 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 12173723 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 50DB5C433DB for ; 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Tue, 30 Mar 2021 13:57:55 -0700 (PDT) From: Kees Cook To: Thomas Gleixner Cc: Kees Cook , Elena Reshetova , x86@kernel.org, Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Mark Rutland , Alexander Potapenko , Alexander Popov , Ard Biesheuvel , Jann Horn , Vlastimil Babka , David Hildenbrand , Mike Rapoport , Andrew Morton , Jonathan Corbet , Randy Dunlap , kernel-hardening@lists.openwall.com, linux-hardening@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v8 4/6] x86/entry: Enable random_kstack_offset support Date: Tue, 30 Mar 2021 13:57:48 -0700 Message-Id: <20210330205750.428816-5-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210330205750.428816-1-keescook@chromium.org> References: <20210330205750.428816-1-keescook@chromium.org> MIME-Version: 1.0 X-Patch-Hashes: v=1; h=sha256; g=5ebd0a02df09ef237ee07421c9f73e94deeaf170; i=np7yed3mY+gWIWkexmB7CyDLgwsIh0xV2RGaksJc7tI=; m=cc9SLz8pm+mdXOKZLHtRjH7FITDzwHCOKmwFrX1p7io=; p=EuIQlileJ2PUD6W0Q1r2arSRAFiVT/zqDgDnM3BVsdE= X-Patch-Sig: m=pgp; i=keescook@chromium.org; s=0x0x8972F4DFDC6DC026; b=iQIzBAABCgAdFiEEpcP2jyKd1g9yPm4TiXL039xtwCYFAmBjkMwACgkQiXL039xtwCam+BAAgyJ fgr3/nTqZn/eYQhhvKuViaCBZLo6l/+H4rxQlTvedji1wqc8cEH1sbGhPpbetwvdv1E5URzjuzmHj KdNMLLG9GNPC46Kj+wXSF6TYDAjM5cN5/gDYo4VtCaToL0CpKQ7ckFQaxaTmeU0fNlFfPSnuB7lkI CiMSuRjNVKM0shhpfIRhpcbrf4pKGtVEI6S2q/Gbf8E9b9CqMBuY6Emsp+RP+E5pIV3MWV+/lWBzW nvw3ooLNtPE4eIIi144Y2qrQIg6kLUEm6bQcJNJ3P5Sl8tPGjpGmC6Na5y+jkQhGtJa8xw8iigpd8 0U/JPVq7sNUY3cC2zuUxjCQndMGeEMC5pqmPYVD5r5EfzWdLjVpna6rY1uIHVjapxIqa47C0SRTR4 5IVkd5ixH0ZqAvdCg7Kmse+MVEFltJ84/dvtt1jVcWTSD810k5uamerLnqHhOTMjxBl870hd23zNW hbNqvHuR9jfFcRe//CAXRojf+E0OfMXwE59pfcMCu+Bd2yJHWaVTzfom6Evz+EH+l/IKLU5TF+fEJ urdE7yT5Eyh8VgMnbExQG1evQIv9UuJeZaNZyqYOT3vycXyscwFxWh3hWDSlYRY7tyBdNfAqe+3U7 o/s2Y+ekI0WlMnWK52ZRX2sTdctKAo9wnnsvddL51SJw6DgLEPu9zjHET5nmRGG4= Allow for a randomized stack offset on a per-syscall basis, with roughly 5-6 bits of entropy, depending on compiler and word size. Since the method of offsetting uses macros, this cannot live in the common entry code (the stack offset needs to be retained for the life of the syscall, which means it needs to happen at the actual entry point). Signed-off-by: Kees Cook Reviewed-by: Thomas Gleixner --- arch/x86/Kconfig | 1 + arch/x86/entry/common.c | 3 +++ arch/x86/include/asm/entry-common.h | 16 ++++++++++++++++ 3 files changed, 20 insertions(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 2792879d398e..4b4ad8ec10d2 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -165,6 +165,7 @@ config X86 select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64 select HAVE_ARCH_USERFAULTFD_WP if X86_64 && USERFAULTFD select HAVE_ARCH_VMAP_STACK if X86_64 + select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET select HAVE_ARCH_WITHIN_STACK_FRAMES select HAVE_ASM_MODVERSIONS select HAVE_CMPXCHG_DOUBLE diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index a2433ae8a65e..810983d7c26f 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -38,6 +38,7 @@ #ifdef CONFIG_X86_64 __visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs) { + add_random_kstack_offset(); nr = syscall_enter_from_user_mode(regs, nr); instrumentation_begin(); @@ -83,6 +84,7 @@ __visible noinstr void do_int80_syscall_32(struct pt_regs *regs) { unsigned int nr = syscall_32_enter(regs); + add_random_kstack_offset(); /* * Subtlety here: if ptrace pokes something larger than 2^32-1 into * orig_ax, the unsigned int return value truncates it. This may @@ -102,6 +104,7 @@ static noinstr bool __do_fast_syscall_32(struct pt_regs *regs) unsigned int nr = syscall_32_enter(regs); int res; + add_random_kstack_offset(); /* * This cannot use syscall_enter_from_user_mode() as it has to * fetch EBP before invoking any of the syscall entry work diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h index 2b87b191b3b8..14ebd2196569 100644 --- a/arch/x86/include/asm/entry-common.h +++ b/arch/x86/include/asm/entry-common.h @@ -2,6 +2,7 @@ #ifndef _ASM_X86_ENTRY_COMMON_H #define _ASM_X86_ENTRY_COMMON_H +#include #include #include @@ -70,6 +71,21 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs, */ current_thread_info()->status &= ~(TS_COMPAT | TS_I386_REGS_POKED); #endif + + /* + * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), + * but not enough for x86 stack utilization comfort. To keep + * reasonable stack head room, reduce the maximum offset to 8 bits. + * + * The actual entropy will be further reduced by the compiler when + * applying stack alignment constraints (see cc_stack_align4/8 in + * arch/x86/Makefile), which will remove the 3 (x86_64) or 2 (ia32) + * low bits from any entropy chosen here. + * + * Therefore, final stack offset entropy will be 5 (x86_64) or + * 6 (ia32) bits. + */ + choose_random_kstack_offset(rdtsc() & 0xFF); } #define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare From patchwork Tue Mar 30 20:57:49 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 12173729 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78804C433DB for ; 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Tue, 30 Mar 2021 13:57:56 -0700 (PDT) From: Kees Cook To: Thomas Gleixner Cc: Kees Cook , Elena Reshetova , x86@kernel.org, Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Mark Rutland , Alexander Potapenko , Alexander Popov , Ard Biesheuvel , Jann Horn , Vlastimil Babka , David Hildenbrand , Mike Rapoport , Andrew Morton , Jonathan Corbet , Randy Dunlap , kernel-hardening@lists.openwall.com, linux-hardening@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v8 5/6] arm64: entry: Enable random_kstack_offset support Date: Tue, 30 Mar 2021 13:57:49 -0700 Message-Id: <20210330205750.428816-6-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210330205750.428816-1-keescook@chromium.org> References: <20210330205750.428816-1-keescook@chromium.org> MIME-Version: 1.0 X-Patch-Hashes: v=1; h=sha256; g=248270d6e87ad6ffcee20e448a3bbf6614f92c8d; i=6FjHrMJQ1a03WxuPiMt8aIK5MW/T0bayLG0SuUm7Wt4=; 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(And include AAPCS rationale AAPCS thanks to Mark Rutland.) In order to avoid unconditional stack canaries on syscall entry (due to the use of alloca()), also disable stack protector to avoid triggering needless checks and slowing down the entry path. As there is no general way to control stack protector coverage with a function attribute[1], this must be disabled at the compilation unit level. This isn't a problem here, though, since stack protector was not triggered before: examining the resulting syscall.o, there are no changes in canary coverage (none before, none now). [1] a working __attribute__((no_stack_protector)) has been added to GCC and Clang but has not been released in any version yet: https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=346b302d09c1e6db56d9fe69048acb32fbb97845 https://reviews.llvm.org/rG4fbf84c1732fca596ad1d6e96015e19760eb8a9b Signed-off-by: Kees Cook --- arch/arm64/Kconfig | 1 + arch/arm64/kernel/Makefile | 5 +++++ arch/arm64/kernel/syscall.c | 16 ++++++++++++++++ 3 files changed, 22 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 1f212b47a48a..2d0e5f544429 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -146,6 +146,7 @@ config ARM64 select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT select HAVE_ARCH_PFN_VALID select HAVE_ARCH_PREL32_RELOCATIONS + select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET select HAVE_ARCH_SECCOMP_FILTER select HAVE_ARCH_STACKLEAK select HAVE_ARCH_THREAD_STRUCT_WHITELIST diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index ed65576ce710..6cc97730790e 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -9,6 +9,11 @@ CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_insn.o = $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE) +# Remove stack protector to avoid triggering unneeded stack canary +# checks due to randomize_kstack_offset. +CFLAGS_REMOVE_syscall.o = -fstack-protector -fstack-protector-strong +CFLAGS_syscall.o += -fno-stack-protector + # Object file lists. obj-y := debug-monitors.o entry.o irq.o fpsimd.o \ entry-common.o entry-fpsimd.o process.o ptrace.o \ diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c index b9cf12b271d7..263d6c1a525f 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -5,6 +5,7 @@ #include #include #include +#include #include #include @@ -43,6 +44,8 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno, { long ret; + add_random_kstack_offset(); + if (scno < sc_nr) { syscall_fn_t syscall_fn; syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)]; @@ -55,6 +58,19 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno, ret = lower_32_bits(ret); regs->regs[0] = ret; + + /* + * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), + * but not enough for arm64 stack utilization comfort. To keep + * reasonable stack head room, reduce the maximum offset to 9 bits. + * + * The actual entropy will be further reduced by the compiler when + * applying stack alignment constraints: the AAPCS mandates a + * 16-byte (i.e. 4-bit) aligned SP at function boundaries. + * + * The resulting 5 bits of entropy is seen in SP[8:4]. + */ + choose_random_kstack_offset(get_random_int() & 0x1FF); } static inline bool has_syscall_work(unsigned long flags) From patchwork Tue Mar 30 20:57:50 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 12173725 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D71AC433E0 for ; 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Tue, 30 Mar 2021 13:57:56 -0700 (PDT) From: Kees Cook To: Thomas Gleixner Cc: Kees Cook , Elena Reshetova , x86@kernel.org, Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Mark Rutland , Alexander Potapenko , Alexander Popov , Ard Biesheuvel , Jann Horn , Vlastimil Babka , David Hildenbrand , Mike Rapoport , Andrew Morton , Jonathan Corbet , Randy Dunlap , kernel-hardening@lists.openwall.com, linux-hardening@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v8 6/6] lkdtm: Add REPORT_STACK for checking stack offsets Date: Tue, 30 Mar 2021 13:57:50 -0700 Message-Id: <20210330205750.428816-7-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210330205750.428816-1-keescook@chromium.org> References: <20210330205750.428816-1-keescook@chromium.org> MIME-Version: 1.0 X-Patch-Hashes: v=1; h=sha256; g=fb815901a1ccc1d9c4ca5c3e3cd3729b7f382fe2; i=b69wRsxT78r/3tM1mGa7N6ME6+rlXyFg15giRWRwPAQ=; m=aFqgiEE+nAZdug79A1F+fVTg9ZceUb0WPE8cbHqssVg=; p=ZQ32/kILkW5AD3nBZHO0VMTp4prIPkm7+DdhCHX8KdA= X-Patch-Sig: m=pgp; i=keescook@chromium.org; s=0x0x8972F4DFDC6DC026; b=iQIzBAABCgAdFiEEpcP2jyKd1g9yPm4TiXL039xtwCYFAmBjkM0ACgkQiXL039xtwCYfLRAAs6I uoWwWDp21BaGNMZo2SuY7bzLTQ4wBsh1OJpZI9l3CnXGSdw3rjz7jQr547uKC02JBkmMzEZ8erZZc OXm9KVlfJUxNAf1Xj1ZCOTuB3x9+E+0QA7hUMrZqjcs42ZBPBNkSPjV9A25U9YqznQ5f+qpoKAWEj hxxEXcX+z7qRe6bJas/EC7OMxjIrCaX9Fzf9HOwub9cZbtwx0dPTxKVeITndj71Nd+oDj/2XxQI+X 9hTzBdUHech+9e7EsTReekwPnRwNq+MAzoYB3JZVfZwT7ewjdvO5Iv6CVMthHmHgut+PjTN00vPS4 OhUYWoQNcsKUhGXXhCoZZ2/MHnjMSsLG8Vpgrb3tQXhiSoeMFXtnamdiasKXt7Jc76LttUOUKyHJo ZHT6pvTFlA8E+uzixb92yFkxiRzqIEGMdMQ3OBJfI2tcnS1KMzsv+Jt1VxL3ySC4aMLFFmM2y1UeI n8OdvXvEabfQwKXEvpIfbAZ6Qm1p7zhujxc9Me7VDJ48cNcSHTtxsNzNXWsEe6PpclfeDU0SglY7l phqtiLzuKHVpdfej4wAJbkaGgOs57NUEso25NbDIc7ZM2syVxWrdxxlP4zgxViiuIq6Yr4W/79kHB 93gnDuL1EJ0D3ib6Nvf+fYfybxPTOR9bKJ+jfn7yAh++prlwwWMuNlPcPXQ0yLfA= For validating the stack offset behavior, report the offset from a given process's first seen stack address. A quick way to measure the entropy: for i in $(seq 1 1000); do echo "REPORT_STACK" >/sys/kernel/debug/provoke-crash/DIRECT done offsets=$(dmesg | grep 'Stack offset' | cut -d: -f3 | sort | uniq -c | sort -n | wc -l) echo "$(uname -m) bits of stack entropy: $(echo "obase=2; $offsets" | bc | wc -L)" Signed-off-by: Kees Cook --- drivers/misc/lkdtm/bugs.c | 17 +++++++++++++++++ drivers/misc/lkdtm/core.c | 1 + drivers/misc/lkdtm/lkdtm.h | 1 + 3 files changed, 19 insertions(+) diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c index 110f5a8538e9..0e8254d0cf0b 100644 --- a/drivers/misc/lkdtm/bugs.c +++ b/drivers/misc/lkdtm/bugs.c @@ -134,6 +134,23 @@ noinline void lkdtm_CORRUPT_STACK_STRONG(void) __lkdtm_CORRUPT_STACK((void *)&data); } +static pid_t stack_pid; +static unsigned long stack_addr; + +void lkdtm_REPORT_STACK(void) +{ + volatile uintptr_t magic; + pid_t pid = task_pid_nr(current); + + if (pid != stack_pid) { + pr_info("Starting stack offset tracking for pid %d\n", pid); + stack_pid = pid; + stack_addr = (uintptr_t)&magic; + } + + pr_info("Stack offset: %d\n", (int)(stack_addr - (uintptr_t)&magic)); +} + void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void) { static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5}; diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c index b2aff4d87c01..8024b6a5cc7f 100644 --- a/drivers/misc/lkdtm/core.c +++ b/drivers/misc/lkdtm/core.c @@ -110,6 +110,7 @@ static const struct crashtype crashtypes[] = { CRASHTYPE(EXHAUST_STACK), CRASHTYPE(CORRUPT_STACK), CRASHTYPE(CORRUPT_STACK_STRONG), + CRASHTYPE(REPORT_STACK), CRASHTYPE(CORRUPT_LIST_ADD), CRASHTYPE(CORRUPT_LIST_DEL), CRASHTYPE(STACK_GUARD_PAGE_LEADING), diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h index 5ae48c64df24..99f90d3e5e9c 100644 --- a/drivers/misc/lkdtm/lkdtm.h +++ b/drivers/misc/lkdtm/lkdtm.h @@ -17,6 +17,7 @@ void lkdtm_LOOP(void); void lkdtm_EXHAUST_STACK(void); void lkdtm_CORRUPT_STACK(void); void lkdtm_CORRUPT_STACK_STRONG(void); +void lkdtm_REPORT_STACK(void); void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void); void lkdtm_SOFTLOCKUP(void); void lkdtm_HARDLOCKUP(void);