[RFC PATCH v1 40/50] arch/*/include/asm/stackprotector.h: Use get_random_canary() consistently
From: George Spelvin <hidden>
Date: 2020-03-28 16:44:53
... in boot_init_stack_canary(). This is the archetypical example of where the extra security of get_random_bytes() is wasted. The canary is only important as long as it's stored in __stack_chk_guard. It's also a great example of code that has been copied around a lot and not updated. Remove the XOR with LINUX_VERSION_CODE as it's pointless; the inclusion of utsname() in init_std_data in the random seeding obviates it. The XOR with the TSC on x86 and mtfb() on powerPC were left in, as I haven't proved them redundant yet. For those, we call get_random_long(), xor, and mask manually. FUNCTIONAL CHANGE: mips and xtensa were changed from 64-bit get_random_long() to 56-bit get_random_canary() to match the others, in accordance with the logic in CANARY_MASK. (We could do 1 bit better and zero *one* of the two high bytes.) Signed-off-by: George Spelvin <redacted> Cc: Russell King <linux@armlinux.org.uk> Cc: linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Ralf Baechle <redacted> Cc: Paul Burton <paulburton@kernel.org> Cc: James Hogan <jhogan@kernel.org> Cc: linux-mips@vger.kernel.org Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <redacted> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: linuxppc-dev@lists.ozlabs.org Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Rich Felker <dalias@libc.org> Cc: linux-sh@vger.kernel.org Cc: Thomas Gleixner <redacted> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: x86@kernel.org Cc: Chris Zankel <chris@zankel.net> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: linux-xtensa@linux-xtensa.org --- arch/arm/include/asm/stackprotector.h | 9 +++------ arch/arm64/include/asm/stackprotector.h | 8 ++------ arch/mips/include/asm/stackprotector.h | 7 ++----- arch/powerpc/include/asm/stackprotector.h | 6 ++---- arch/sh/include/asm/stackprotector.h | 8 ++------ arch/x86/include/asm/stackprotector.h | 4 ++-- arch/xtensa/include/asm/stackprotector.h | 7 ++----- 7 files changed, 15 insertions(+), 34 deletions(-)
diff --git a/arch/arm/include/asm/stackprotector.h b/arch/arm/include/asm/stackprotector.h
index 72a20c3a0a90b..88c66fec1b5f4 100644
--- a/arch/arm/include/asm/stackprotector.h
+++ b/arch/arm/include/asm/stackprotector.h@@ -30,17 +30,14 @@ extern unsigned long __stack_chk_guard; */ static __always_inline void boot_init_stack_canary(void) { - unsigned long canary; - /* Try to get a semi random initial value. */ - get_random_bytes(&canary, sizeof(canary)); - canary ^= LINUX_VERSION_CODE; + unsigned long canary = get_random_canary(); current->stack_canary = canary; #ifndef CONFIG_STACKPROTECTOR_PER_TASK - __stack_chk_guard = current->stack_canary; + __stack_chk_guard = canary; #else - current_thread_info()->stack_canary = current->stack_canary; + current_thread_info()->stack_canary = canary; #endif }
diff --git a/arch/arm64/include/asm/stackprotector.h b/arch/arm64/include/asm/stackprotector.h
index 5884a2b028277..705f60b9df85e 100644
--- a/arch/arm64/include/asm/stackprotector.h
+++ b/arch/arm64/include/asm/stackprotector.h@@ -26,16 +26,12 @@ extern unsigned long __stack_chk_guard; */ static __always_inline void boot_init_stack_canary(void) { - unsigned long canary; - /* Try to get a semi random initial value. */ - get_random_bytes(&canary, sizeof(canary)); - canary ^= LINUX_VERSION_CODE; - canary &= CANARY_MASK; + unsigned long canary = get_random_canary(); current->stack_canary = canary; if (!IS_ENABLED(CONFIG_STACKPROTECTOR_PER_TASK)) - __stack_chk_guard = current->stack_canary; + __stack_chk_guard = canary; } #endif /* _ASM_STACKPROTECTOR_H */
diff --git a/arch/mips/include/asm/stackprotector.h b/arch/mips/include/asm/stackprotector.h
index 68d4be9e12547..6d1e4652152bc 100644
--- a/arch/mips/include/asm/stackprotector.h
+++ b/arch/mips/include/asm/stackprotector.h@@ -28,14 +28,11 @@ extern unsigned long __stack_chk_guard; */ static __always_inline void boot_init_stack_canary(void) { - unsigned long canary; - /* Try to get a semi random initial value. */ - get_random_bytes(&canary, sizeof(canary)); - canary ^= LINUX_VERSION_CODE; + unsigned long canary = get_random_canary(); current->stack_canary = canary; - __stack_chk_guard = current->stack_canary; + __stack_chk_guard = canary; } #endif /* _ASM_STACKPROTECTOR_H */
diff --git a/arch/powerpc/include/asm/stackprotector.h b/arch/powerpc/include/asm/stackprotector.h
index 1c8460e235838..76577b72ef736 100644
--- a/arch/powerpc/include/asm/stackprotector.h
+++ b/arch/powerpc/include/asm/stackprotector.h@@ -21,12 +21,10 @@ */ static __always_inline void boot_init_stack_canary(void) { - unsigned long canary; - /* Try to get a semi random initial value. */ - canary = get_random_canary(); + unsigned long canary = get_random_long(); + canary ^= mftb(); - canary ^= LINUX_VERSION_CODE; canary &= CANARY_MASK; current->stack_canary = canary;
diff --git a/arch/sh/include/asm/stackprotector.h b/arch/sh/include/asm/stackprotector.h
index 35616841d0a1c..a9ef619c8a0ec 100644
--- a/arch/sh/include/asm/stackprotector.h
+++ b/arch/sh/include/asm/stackprotector.h@@ -15,15 +15,11 @@ extern unsigned long __stack_chk_guard; */ static __always_inline void boot_init_stack_canary(void) { - unsigned long canary; - /* Try to get a semi random initial value. */ - get_random_bytes(&canary, sizeof(canary)); - canary ^= LINUX_VERSION_CODE; - canary &= CANARY_MASK; + unsigned long canary = get_random_canary(); current->stack_canary = canary; - __stack_chk_guard = current->stack_canary; + __stack_chk_guard = canary; } #endif /* __ASM_SH_STACKPROTECTOR_H */
diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
index 91e29b6a86a5e..af74fd3130cf4 100644
--- a/arch/x86/include/asm/stackprotector.h
+++ b/arch/x86/include/asm/stackprotector.h@@ -72,9 +72,9 @@ static __always_inline void boot_init_stack_canary(void) * there it already has some randomness on most systems. Later * on during the bootup the random pool has true entropy too. */ - get_random_bytes(&canary, sizeof(canary)); + canary = get_random_u64(); tsc = rdtsc(); - canary += tsc + (tsc << 32UL); + canary += tsc + (tsc << 32); canary &= CANARY_MASK; current->stack_canary = canary;
diff --git a/arch/xtensa/include/asm/stackprotector.h b/arch/xtensa/include/asm/stackprotector.h
index e368f94fd2af3..9807fd80e5a8e 100644
--- a/arch/xtensa/include/asm/stackprotector.h
+++ b/arch/xtensa/include/asm/stackprotector.h@@ -27,14 +27,11 @@ extern unsigned long __stack_chk_guard; */ static __always_inline void boot_init_stack_canary(void) { - unsigned long canary; - /* Try to get a semi random initial value. */ - get_random_bytes(&canary, sizeof(canary)); - canary ^= LINUX_VERSION_CODE; + unsigned long canary = get_random_canary(); current->stack_canary = canary; - __stack_chk_guard = current->stack_canary; + __stack_chk_guard = canary; } #endif /* _ASM_STACKPROTECTOR_H */
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2.26.0