From patchwork Thu Apr 1 23:23:46 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 12179875 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 1646FC433B4 for ; Thu, 1 Apr 2021 23:25:00 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 1A81661105 for ; Thu, 1 Apr 2021 23:24:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1A81661105 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-21140-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 11786 invoked by uid 550); 1 Apr 2021 23:24:09 -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 11675 invoked from network); 1 Apr 2021 23:24:06 -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=dHwr6OVFfk7s7Yw8a90FyZmnLv02IEGSs6EhbG8UN8M=; b=apoCPv6eRxC+65o8Yfokym7TMqmTLua+kwS5uawMkAr+K8bzn0V6/+UNB+E8jjMTT9 kqBvLjd/Y8r/2j+FcF251klrukr4C2g4wEp9/G2iZwIGl2vQVJKEhV3vbmAeJ9arWHcM k8t+ERXme2Uowb4UveF5DKhHLDGzwVc27v6PY= 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=dHwr6OVFfk7s7Yw8a90FyZmnLv02IEGSs6EhbG8UN8M=; b=k/z43FhhAbnDmm4jR2z+dwAdLJwjJ5RVNw7BR2zhefLAiU0vwfIKWcnbAZwEa8TPOl Cd4YcvigCWn6e9YD0pbifWkvkIctqB90DZ1T3XiJ6o/PuDH1pbi3PbOjx2TaYHcHVUPU LvuMaIATQkCyQBfnCMSR0V6pwzXKw/i2EGIAJcf2A/GEBWs+ON9LnJsfyNSteQCvaNZX qCqdZTKKHpvAWiqY2+mrbgJNUcOQ5kzBpj+ajhL9G1Iahb86vHmurdIAMgWvQgiHgo2M MQiFrLzbpP0/ViAAJXsAWD8ACIHbZh/5mhpWEOo7HDBXs8Dt6q5JrnkGqqd3eYgad+ov eSrA== X-Gm-Message-State: AOAM532V4utUaZWRn3QWDMJH8tJMHXUgNBSTNk4yWBFhg2UzFdrJqsVT i6RctPji3IXeMQQ2rK+G9gKmjQ== X-Google-Smtp-Source: ABdhPJy0JI+h7arv5jEq6paI9Bu5w08cDNSCg/uQ/t7RP6xwDr38VSpWxgu747yOW+trYuYmyvFaZA== X-Received: by 2002:a62:b412:0:b029:21f:6b06:7bdd with SMTP id h18-20020a62b4120000b029021f6b067bddmr9677058pfn.51.1617319434704; Thu, 01 Apr 2021 16:23:54 -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 v10 5/6] arm64: entry: Enable random_kstack_offset support Date: Thu, 1 Apr 2021 16:23:46 -0700 Message-Id: <20210401232347.2791257-6-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210401232347.2791257-1-keescook@chromium.org> References: <20210401232347.2791257-1-keescook@chromium.org> MIME-Version: 1.0 X-Patch-Hashes: v=1; h=sha256; g=248270d6e87ad6ffcee20e448a3bbf6614f92c8d; i=6FjHrMJQ1a03WxuPiMt8aIK5MW/T0bayLG0SuUm7Wt4=; m=DW/OKOjAEidoxl6ODEV6zN0c7U/uCvK1t/uZsIkKPaM=; p=nb+ZCQAESoMtgqRKEEjn/wowCv7zZGeRTSUAEFbjSEQ= X-Patch-Sig: m=pgp; i=keescook@chromium.org; s=0x0x8972F4DFDC6DC026; b=iQIzBAABCgAdFiEEpcP2jyKd1g9yPm4TiXL039xtwCYFAmBmVgIACgkQiXL039xtwCZDLw//WsN q3e+PfWfPV1g3MMiPrlRGvZeP5grL9TtxqK1tGNvEy6dp+ulJLVcVDUgjKq6d2+6/ZtpF/CXp1Djm YjJGAOaElG7IEw7D5rWkdaIDh/+dJB9i4OG7OQStbX2RdOTztew9FhzttIrvtz9CdY/62YtNZwfSM MMJuDLR6sDqH/hCS9vInn5lqd459ACg1MQxu5GoytTWRNX8WWvf5JQzZhQjfEc8krX0rpOsQzDr5t mO5emz5pHZsbxfKob6wQsl+exwaKhfwPphM0Tn5RCDnVvf9bTDJVhQnNwIT2+Q378sZ5hcpwvz8Yx 3mhh09xaCK/zQ3/kmN1gqG6pPlCtoxRBbEFTzbhj16pX65K+bS5BZ5XWM3ugP8EXfXyWrpo52dSr5 /t6uVKyB16iSTt7H9rEcp1wXS1076HCT6M8Wde/qn1X2QK1ZLA0cesEWm/X4sk/w1Ve1TWe6PmQpW Nk6T3IyLa/fkxj14KMiTNTz2sMFoeqV/i4d24nIL+3TQG5LqAqG/9iT56DYYHkYs11nmeEHf4qbLV bn/R7twlh65mDdXZ/L6iFluiC+fm1yLrDq4JIwtrmQJbUqE0m9f8KUCzMgXfYFSY8lb5Wo0OxNxOr uzdIl+VgJ/ySASy1+o5Q6GjAhge97rgSd/h8Isb33l3zzjkc6/vquWyNirJA8dIg= Allow for a randomized stack offset on a per-syscall basis, with roughly 5 bits of entropy. (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 Acked-by: Will Deacon --- 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)