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Message-Id: <202003281643.02SGhM0T009250@sdf.org>
Date: Tue, 10 Dec 2019 00:35:14 -0500
From: George Spelvin <lkml@....org>
To: linux-kernel@...r.kernel.org, lkml@....org
Cc: Russell King <linux@...linux.org.uk>,
linux-arm-kernel@...ts.infradead.org,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Ralf Baechle <ralf@...ux-mips.org>,
Paul Burton <paulburton@...nel.org>,
James Hogan <jhogan@...nel.org>, linux-mips@...r.kernel.org,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Michael Ellerman <mpe@...erman.id.au>,
linuxppc-dev@...ts.ozlabs.org,
Yoshinori Sato <ysato@...rs.sourceforge.jp>,
Rich Felker <dalias@...c.org>, linux-sh@...r.kernel.org,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
Chris Zankel <chris@...kel.net>,
Max Filippov <jcmvbkbc@...il.com>,
linux-xtensa@...ux-xtensa.org
Subject: [RFC PATCH v1 40/50] arch/*/include/asm/stackprotector.h: Use
get_random_canary() consistently
... 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@....org>
Cc: Russell King <linux@...linux.org.uk>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Ralf Baechle <ralf@...ux-mips.org>
Cc: Paul Burton <paulburton@...nel.org>
Cc: James Hogan <jhogan@...nel.org>
Cc: linux-mips@...r.kernel.org
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: Yoshinori Sato <ysato@...rs.sourceforge.jp>
Cc: Rich Felker <dalias@...c.org>
Cc: linux-sh@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
Cc: Chris Zankel <chris@...kel.net>
Cc: Max Filippov <jcmvbkbc@...il.com>
Cc: linux-xtensa@...ux-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 */
--
2.26.0
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