... 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 <[email protected]>
Cc: Russell King <[email protected]>
Cc: [email protected]
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Paul Burton <[email protected]>
Cc: James Hogan <[email protected]>
Cc: [email protected]
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: [email protected]
Cc: Yoshinori Sato <[email protected]>
Cc: Rich Felker <[email protected]>
Cc: [email protected]
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Cc: Chris Zankel <[email protected]>
Cc: Max Filippov <[email protected]>
Cc: [email protected]
---
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
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 <[email protected]>
> Cc: Russell King <[email protected]>
> Cc: [email protected]
> Cc: Catalin Marinas <[email protected]>
> Cc: Will Deacon <[email protected]>
> Cc: Ralf Baechle <[email protected]>
> Cc: Paul Burton <[email protected]>
> Cc: James Hogan <[email protected]>
> Cc: [email protected]
> Cc: Benjamin Herrenschmidt <[email protected]>
> Cc: Paul Mackerras <[email protected]>
> Cc: Michael Ellerman <[email protected]>
> Cc: [email protected]
> Cc: Yoshinori Sato <[email protected]>
> Cc: Rich Felker <[email protected]>
> Cc: [email protected]
> Cc: Thomas Gleixner <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Borislav Petkov <[email protected]>
> Cc: "H. Peter Anvin" <[email protected]>
> Cc: [email protected]
> Cc: Chris Zankel <[email protected]>
> Cc: Max Filippov <[email protected]>
> Cc: [email protected]
> ---
> 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