From patchwork Mon Jun 22 19:31:46 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 11618845 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 0595414B7 for ; Mon, 22 Jun 2020 19:32:50 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 641A9207DD for ; Mon, 22 Jun 2020 19:32:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="BKy23l2w" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 641A9207DD 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-19038-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 19959 invoked by uid 550); 22 Jun 2020 19:32:09 -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: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 19832 invoked from network); 22 Jun 2020 19:32:07 -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=zcPQ3teAeONtZCSjASMvWQH+0FGked91D84DWb3cnhA=; b=BKy23l2w1m43ZpBXQM2fDRryt6KkrHZIrILWSDueLTLg7JkO/xXIBdrpxBtpXqG8Eo C+whcf+rw091oqysj+R7yNmqCI48ZtM7rhgZGnobI7SE5xNIel15JCPoNXr8RLA/8gKA FUXw0i2C4M8kbA9Vh9+15Qvp6mVOpj0mucLag= 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=zcPQ3teAeONtZCSjASMvWQH+0FGked91D84DWb3cnhA=; b=lSdVlcs+dLlcQ7ziJAckQKCuyzQ6xaTgOf3GLAatx+YwErnePx5ybA8KfJyCMPT1Ph g3tzE4eLM31wr0wam5AFhEpsWIAGUvtaGRw7cvCRWXHbs5qqfP/QKeg5gEb7shHYzANm Et+Q7uDo7norX03QY4VlU2lvvKUj/GSSXepx31ud/Xh8xozitMC30qJ7+aP8tFPWBP+b go9xhkkHYUnnQQ39s4pgSPuCfbr91AK//Wdwkl4hjEi4JkhWbEHhlvh/+ol7TzPdSlg+ 5DjCb+orHtIckk/+H4B5yC6EdDsr0pOFo9vEpgu8eOFOB0PziPztmYtewRxJfaYoXHr/ Qgvg== X-Gm-Message-State: AOAM532vCealYK6MfoHqYGedgoJwTKjn+TmGYjBcnyA7Za6fraYEYsN5 eKWSXP0eomUH7LnOo70VdyvVHg== X-Google-Smtp-Source: ABdhPJwITrbj7E83VXsf9fWrxu//1aHMGodlvPkjapka8zNgM+eZ+A/1KAwdust7T+yhFUZyNvTBXw== X-Received: by 2002:a63:3f42:: with SMTP id m63mr14501829pga.310.1592854314990; Mon, 22 Jun 2020 12:31:54 -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 , kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v4 5/5] arm64: entry: Enable random_kstack_offset support Date: Mon, 22 Jun 2020 12:31:46 -0700 Message-Id: <20200622193146.2985288-6-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200622193146.2985288-1-keescook@chromium.org> References: <20200622193146.2985288-1-keescook@chromium.org> MIME-Version: 1.0 Allow for a randomized stack offset on a per-syscall basis, with roughly 5 bits of entropy. In order to avoid unconditional stack canaries on syscall entry, also downgrade from -fstack-protector-strong to -fstack-protector to avoid triggering checks due to alloca(). Examining the resulting syscall.o, sees no changes in canary coverage (none before, none now). Signed-off-by: Kees Cook --- arch/arm64/Kconfig | 1 + arch/arm64/kernel/Makefile | 5 +++++ arch/arm64/kernel/syscall.c | 10 ++++++++++ 3 files changed, 16 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index a4a094bedcb2..2902e5316e1a 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -135,6 +135,7 @@ config ARM64 select HAVE_ARCH_MMAP_RND_BITS select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT 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 151f28521f1e..39fc23d3770b 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -11,6 +11,11 @@ CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_insn.o = $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE) +# Downgrade to -fstack-protector to avoid triggering unneeded stack canary +# checks due to randomize_kstack_offset. +CFLAGS_REMOVE_syscall.o += -fstack-protector-strong +CFLAGS_syscall.o += $(subst -fstack-protector-strong,-fstack-protector,$(filter -fstack-protector-strong,$(KBUILD_CFLAGS))) + # 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 5f5b868292f5..00d3c84db9cd 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -5,6 +5,7 @@ #include #include #include +#include #include #include @@ -42,6 +43,8 @@ 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)]; @@ -51,6 +54,13 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno, } regs->regs[0] = ret; + + /* + * Since the compiler chooses a 4 bit alignment for the stack, + * let's save one additional bit (9 total), which gets us up + * near 5 bits of entropy. + */ + choose_random_kstack_offset(get_random_int() & 0x1FF); } static inline bool has_syscall_work(unsigned long flags)