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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id f8sm10635773pgc.75.2020.04.06.16.16.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Apr 2020 16:16:10 -0700 (PDT) From: Kees Cook To: Thomas Gleixner Subject: [PATCH v3 4/5] x86/entry: Enable random_kstack_offset support Date: Mon, 6 Apr 2020 16:16:05 -0700 Message-Id: <20200406231606.37619-5-keescook@chromium.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200406231606.37619-1-keescook@chromium.org> References: <20200406231606.37619-1-keescook@chromium.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200406_161614_667912_62D1C863 X-CRM114-Status: GOOD ( 15.22 ) X-Spam-Score: -0.4 (/) X-Spam-Report: SpamAssassin version 3.4.4 on bombadil.infradead.org summary: Content analysis details: (-0.4 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at https://www.dnswl.org/, no trust [2607:f8b0:4864:20:0:0:0:642 listed in] [list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain -0.2 DKIMWL_WL_HIGH DKIMwl.org - Whitelisted High sender X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Kees Cook , Jann Horn , Ard Biesheuvel , Peter Zijlstra , Catalin Marinas , x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Alexander Potapenko , linux-arm-kernel@lists.infradead.org, Andy Lutomirski , kernel-hardening@lists.openwall.com, Will Deacon , Elena Reshetova Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org 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 canary coverage changes to common.o, this also removes canaries in other functions, due to a handful of declarations of "__u64 args[6]" (from seccomp) and "unsigned long args[6]" (from tracepoints), but their accesses are indexed (instead of via dynamically sized linear reads/writes) so the risk of removing useful mitigation coverage here is very low. Signed-off-by: Kees Cook --- arch/x86/Kconfig | 1 + arch/x86/entry/Makefile | 9 +++++++++ arch/x86/entry/common.c | 12 +++++++++++- 3 files changed, 21 insertions(+), 1 deletion(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index beea77046f9b..b9d449581eb6 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -150,6 +150,7 @@ config X86 select HAVE_ARCH_TRANSPARENT_HUGEPAGE select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64 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/Makefile b/arch/x86/entry/Makefile index 06fc70cf5433..7b40e6ae2618 100644 --- a/arch/x86/entry/Makefile +++ b/arch/x86/entry/Makefile @@ -7,6 +7,15 @@ OBJECT_FILES_NON_STANDARD_entry_64_compat.o := y CFLAGS_syscall_64.o += $(call cc-option,-Wno-override-init,) CFLAGS_syscall_32.o += $(call cc-option,-Wno-override-init,) + +# Downgrade to -fstack-protector to avoid triggering unneeded stack canary +# checks due to randomize_kstack_offset. This also removes canaries in +# other places as well, due to a handful of declarations of __u64 args[6] +# (seccomp) and unsigned long args[6] (tracepoints), but their accesses +# are indexed (instead of via dynamically sized linear reads/writes) so +# the risk of removing useful mitigation coverage here is very low. +CFLAGS_common.o += $(subst -fstack-protector-strong,-fstack-protector,$(filter -fstack-protector-strong,$(KBUILD_CFLAGS))) + obj-y := entry_$(BITS).o thunk_$(BITS).o syscall_$(BITS).o obj-y += common.o diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 9747876980b5..086d7af570af 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -26,6 +26,7 @@ #include #include #include +#include #include #include @@ -189,6 +190,13 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) lockdep_assert_irqs_disabled(); lockdep_sys_exit(); + /* + * x86_64 stack alignment means 3 bits are ignored, so keep + * the top 5 bits. x86_32 needs only 2 bits of alignment, so + * the top 6 bits will be used. + */ + choose_random_kstack_offset(rdtsc() & 0xFF); + cached_flags = READ_ONCE(ti->flags); if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) @@ -283,6 +291,7 @@ __visible void do_syscall_64(unsigned long nr, struct pt_regs *regs) { struct thread_info *ti; + add_random_kstack_offset(); enter_from_user_mode(); local_irq_enable(); ti = current_thread_info(); @@ -355,6 +364,7 @@ static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs) /* Handles int $0x80 */ __visible void do_int80_syscall_32(struct pt_regs *regs) { + add_random_kstack_offset(); enter_from_user_mode(); local_irq_enable(); do_syscall_32_irqs_on(regs); @@ -378,8 +388,8 @@ __visible long do_fast_syscall_32(struct pt_regs *regs) */ regs->ip = landing_pad; + add_random_kstack_offset(); enter_from_user_mode(); - local_irq_enable(); /* Fetch EBP from where the vDSO stashed it. */