From: Kees Cook <keescook@chromium.org> To: Thomas Gleixner <tglx@linutronix.de> Cc: Kees Cook <keescook@chromium.org>, Elena Reshetova <elena.reshetova@intel.com>, x86@kernel.org, Andy Lutomirski <luto@kernel.org>, Peter Zijlstra <peterz@infradead.org>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Mark Rutland <mark.rutland@arm.com>, Alexander Potapenko <glider@google.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Jann Horn <jannh@google.com>, kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 5/5] arm64: entry: Enable random_kstack_offset support Date: Mon, 6 Apr 2020 16:16:06 -0700 [thread overview] Message-ID: <20200406231606.37619-6-keescook@chromium.org> (raw) In-Reply-To: <20200406231606.37619-1-keescook@chromium.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 syscall.o, sees no changes in canary coverage (none before, none now). Signed-off-by: Kees Cook <keescook@chromium.org> --- arch/arm64/Kconfig | 1 + arch/arm64/kernel/Makefile | 4 ++++ arch/arm64/kernel/syscall.c | 10 ++++++++++ 3 files changed, 15 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 0b30e884e088..4d5aa4959f72 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -127,6 +127,7 @@ 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 fc6488660f64..b89005f125d6 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -11,6 +11,10 @@ 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_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 a12c0c88d345..238dbd753b44 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -5,6 +5,7 @@ #include <linux/errno.h> #include <linux/nospec.h> #include <linux/ptrace.h> +#include <linux/randomize_kstack.h> #include <linux/syscalls.h> #include <asm/daifflags.h> @@ -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) -- 2.20.1
WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org> To: Thomas Gleixner <tglx@linutronix.de> Cc: Mark Rutland <mark.rutland@arm.com>, Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Peter Zijlstra <peterz@infradead.org>, Catalin Marinas <catalin.marinas@arm.com>, x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Alexander Potapenko <glider@google.com>, linux-arm-kernel@lists.infradead.org, Andy Lutomirski <luto@kernel.org>, kernel-hardening@lists.openwall.com, Will Deacon <will@kernel.org>, Elena Reshetova <elena.reshetova@intel.com> Subject: [PATCH v3 5/5] arm64: entry: Enable random_kstack_offset support Date: Mon, 6 Apr 2020 16:16:06 -0700 [thread overview] Message-ID: <20200406231606.37619-6-keescook@chromium.org> (raw) In-Reply-To: <20200406231606.37619-1-keescook@chromium.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 syscall.o, sees no changes in canary coverage (none before, none now). Signed-off-by: Kees Cook <keescook@chromium.org> --- arch/arm64/Kconfig | 1 + arch/arm64/kernel/Makefile | 4 ++++ arch/arm64/kernel/syscall.c | 10 ++++++++++ 3 files changed, 15 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 0b30e884e088..4d5aa4959f72 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -127,6 +127,7 @@ 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 fc6488660f64..b89005f125d6 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -11,6 +11,10 @@ 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_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 a12c0c88d345..238dbd753b44 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -5,6 +5,7 @@ #include <linux/errno.h> #include <linux/nospec.h> #include <linux/ptrace.h> +#include <linux/randomize_kstack.h> #include <linux/syscalls.h> #include <asm/daifflags.h> @@ -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) -- 2.20.1 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-04-06 23:16 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-04-06 23:16 [PATCH v3 0/5] Optionally randomize kernel stack offset each syscall Kees Cook 2020-04-06 23:16 ` Kees Cook 2020-04-06 23:16 ` [PATCH v3 1/5] jump_label: Provide CONFIG-driven build state defaults Kees Cook 2020-04-06 23:16 ` Kees Cook 2020-04-06 23:16 ` [PATCH v3 2/5] init_on_alloc: Unpessimize default-on builds Kees Cook 2020-04-06 23:16 ` Kees Cook 2020-04-06 23:16 ` [PATCH v3 3/5] stack: Optionally randomize kernel stack offset each syscall Kees Cook 2020-04-06 23:16 ` Kees Cook 2020-04-06 23:16 ` [PATCH v3 4/5] x86/entry: Enable random_kstack_offset support Kees Cook 2020-04-06 23:16 ` Kees Cook 2020-04-06 23:16 ` Kees Cook [this message] 2020-04-06 23:16 ` [PATCH v3 5/5] arm64: entry: " Kees Cook
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