On Tue, Apr 21, 2020 at 04:15:31PM +0100, Will Deacon wrote:
> do_csum() over-reads the source buffer and therefore abuses
> READ_ONCE_NOCHECK() to avoid tripping up KASAN. In preparation for
> READ_ONCE_NOCHECK() becoming a macro, and therefore losing its
> '__no_sanitize_address' annotation, just annotate do_csum() explicitly
> and fall back to normal loads.
>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Robin Murphy <robin.murphy@xxxxxxx>
> Signed-off-by: Will Deacon <will@xxxxxxxxxx>
>From a functional perspective:
Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
I know that Robin had a concern w.r.t. how this would affect the
codegen, but I think we can follow that up after the series as a whole
is merged.
Thanks,
Mark.
> ---
> arch/arm64/lib/csum.c | 20 ++++++++++++--------
> 1 file changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/lib/csum.c b/arch/arm64/lib/csum.c
> index 60eccae2abad..78b87a64ca0a 100644
> --- a/arch/arm64/lib/csum.c
> +++ b/arch/arm64/lib/csum.c
> @@ -14,7 +14,11 @@ static u64 accumulate(u64 sum, u64 data)
> return tmp + (tmp >> 64);
> }
>
> -unsigned int do_csum(const unsigned char *buff, int len)
> +/*
> + * We over-read the buffer and this makes KASAN unhappy. Instead, disable
> + * instrumentation and call kasan explicitly.
> + */
> +unsigned int __no_sanitize_address do_csum(const unsigned char *buff, int len)
> {
> unsigned int offset, shift, sum;
> const u64 *ptr;
> @@ -42,7 +46,7 @@ unsigned int do_csum(const unsigned char *buff, int len)
> * odd/even alignment, and means we can ignore it until the very end.
> */
> shift = offset * 8;
> - data = READ_ONCE_NOCHECK(*ptr++);
> + data = *ptr++;
> #ifdef __LITTLE_ENDIAN
> data = (data >> shift) << shift;
> #else
> @@ -58,10 +62,10 @@ unsigned int do_csum(const unsigned char *buff, int len)
> while (unlikely(len > 64)) {
> __uint128_t tmp1, tmp2, tmp3, tmp4;
>
> - tmp1 = READ_ONCE_NOCHECK(*(__uint128_t *)ptr);
> - tmp2 = READ_ONCE_NOCHECK(*(__uint128_t *)(ptr + 2));
> - tmp3 = READ_ONCE_NOCHECK(*(__uint128_t *)(ptr + 4));
> - tmp4 = READ_ONCE_NOCHECK(*(__uint128_t *)(ptr + 6));
> + tmp1 = *(__uint128_t *)ptr;
> + tmp2 = *(__uint128_t *)(ptr + 2);
> + tmp3 = *(__uint128_t *)(ptr + 4);
> + tmp4 = *(__uint128_t *)(ptr + 6);
>
> len -= 64;
> ptr += 8;
> @@ -85,7 +89,7 @@ unsigned int do_csum(const unsigned char *buff, int len)
> __uint128_t tmp;
>
> sum64 = accumulate(sum64, data);
> - tmp = READ_ONCE_NOCHECK(*(__uint128_t *)ptr);
> + tmp = *(__uint128_t *)ptr;
>
> len -= 16;
> ptr += 2;
> @@ -100,7 +104,7 @@ unsigned int do_csum(const unsigned char *buff, int len)
> }
> if (len > 0) {
> sum64 = accumulate(sum64, data);
> - data = READ_ONCE_NOCHECK(*ptr);
> + data = *ptr;
> len -= 8;
> }
> /*
> --
> 2.26.1.301.g55bc3eb7cb9-goog
>
