| Message ID | 202003281643.02SGhM0T009250@sdf.org (mailing list archive) |
|---|---|
| State | RFC |
| Headers | show |
| Series | None | expand |
On Tue, Dec 10, 2019 at 12:35:14AM -0500, George Spelvin wrote: > ... 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 <lkml@sdf.org> > 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 <ralf@linux-mips.org> > 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 <paulus@samba.org> > 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 <tglx@linutronix.de> > 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(-) Just found this kicking around in the depths of my inbox. Is the series dead? Will
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 */
... 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 <lkml@sdf.org> 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 <ralf@linux-mips.org> 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 <paulus@samba.org> 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 <tglx@linutronix.de> 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(-)