Re: [RFC PATCH v1 40/50] arch/*/include/asm/stackprotector.h: Use get_random_canary() consistently

[Will Deacon]

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@xxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
> Cc: Paul Burton <paulburton@xxxxxxxxxx>
> Cc: James Hogan <jhogan@xxxxxxxxxx>
> Cc: linux-mips@xxxxxxxxxxxxxxx
> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Cc: Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx>
> Cc: Rich Felker <dalias@xxxxxxxx>
> Cc: linux-sh@xxxxxxxxxxxxxxx
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc:  "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: Chris Zankel <chris@xxxxxxxxxx>
> Cc: Max Filippov <jcmvbkbc@xxxxxxxxx>
> Cc: linux-xtensa@xxxxxxxxxxxxxxxx
> ---
>  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