target/linux/generic/backport-5.4/042-v5.5-arm64-csum-Fix-pathological-zero-length-calls.patch

   1 From: Robin Murphy <robin.murphy@arm.com>
   2 Date: Fri, 17 Jan 2020 15:48:39 +0000
   3 Subject: [PATCH] arm64: csum: Fix pathological zero-length calls
   4
   5 In validating the checksumming results of the new routine, I sadly
   6 neglected to test its not-checksumming results. Thus it slipped through
   7 that the one case where @buff is already dword-aligned and @len = 0
   8 manages to defeat the tail-masking logic and behave as if @len = 8.
   9 For a zero length it doesn't make much sense to deference @buff anyway,
  10 so just add an early return (which has essentially zero impact on
  11 performance).
  12
  13 Signed-off-by: Robin Murphy <robin.murphy@arm.com>
  14 Signed-off-by: Will Deacon <will@kernel.org>
  15 ---
  16
  17 --- a/arch/arm64/lib/csum.c
  18 +++ b/arch/arm64/lib/csum.c
  19 @@ -20,6 +20,9 @@ unsigned int do_csum(const unsigned char
  20         const u64 *ptr;
  21         u64 data, sum64 = 0;
  22
  23 +       if (unlikely(len == 0))
  24 +               return 0;
  25 +
  26         offset = (unsigned long)buff & 7;
  27         /*
  28          * This is to all intents and purposes safe, since rounding down cannot