[PATCH 60/82] powerpc: Refactor intentional wrap-around test

[Michael Ellerman]

Kees Cook <keescook at chromium.org> writes:
> In an effort to separate intentional arithmetic wrap-around from
> unexpected wrap-around, we need to refactor places that depend on this
> kind of math. One of the most common code patterns of this is:
>
> 	VAR + value < VAR
>
> Notably, this is considered "undefined behavior" for signed and pointer
> types, which the kernel works around by using the -fno-strict-overflow
> option in the build[1] (which used to just be -fwrapv). Regardless, we
> want to get the kernel source to the position where we can meaningfully
> instrument arithmetic wrap-around conditions and catch them when they
> are unexpected, regardless of whether they are signed[2], unsigned[3],
> or pointer[4] types.
>
> Refactor open-coded wrap-around addition test to use add_would_overflow().
> This paves the way to enabling the wrap-around sanitizers in the future.
>
> Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
> Link: https://github.com/KSPP/linux/issues/26 [2]
> Link: https://github.com/KSPP/linux/issues/27 [3]
> Link: https://github.com/KSPP/linux/issues/344 [4]
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> Cc: Nicholas Piggin <npiggin at gmail.com>
> Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar at kernel.org>
> Cc: "Naveen N. Rao" <naveen.n.rao at linux.ibm.com>
> Cc: Mahesh Salgaonkar <mahesh at linux.ibm.com>
> Cc: Vasant Hegde <hegdevasant at linux.vnet.ibm.com>
> Cc: dingsenjie <dingsenjie at yulong.com>
> Cc: linuxppc-dev at lists.ozlabs.org
> Cc: Aneesh Kumar K.V <aneesh.kumar at kernel.org>
> Cc: Naveen N. Rao <naveen.n.rao at linux.ibm.com>
> Signed-off-by: Kees Cook <keescook at chromium.org>
> ---
>  arch/powerpc/platforms/powernv/opal-prd.c | 2 +-
>  arch/powerpc/xmon/xmon.c                  | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)

Acked-by: Michael Ellerman <mpe at ellerman.id.au> (powerpc)

cheers