[PATCH 0/2] word-at-a-time: let KASAN see load_unaligned_zeropad()

[Qiliang Yuan]

load_unaligned_zeropad() is inline assembly, so KASAN and KCSAN never
see the word loads that sized_strscpy(), the dcache name compare, path
name hashing and x86 csum_partial() do through it. While reviewing a
strscpy() KASAN fix, Peter Collingbourne suggested checking the first
byte inside load_unaligned_zeropad() itself, as read_word_at_a_time()
does [1].

Patch 1 adds that check on the six architectures that implement
load_unaligned_zeropad(). Patch 2 adds a KASAN KUnit case for it.

This is independent of the strscpy() fix, which makes sized_strscpy()
copy byte by byte under software KASAN so that every byte it reads is
checked. Either can be applied without the other.

[1] https://lore.kernel.org/r/CAPQLkRhXZwozmfhNd_PEx1ihwdH1_5qthP6PANYJ_m-v9vfQTw@mail.gmail.com

Signed-off-by: Qiliang Yuan <odys.yuan at gmail.com>
---
Qiliang Yuan (2):
      word-at-a-time: check the first byte in load_unaligned_zeropad()
      kasan/test: cover load_unaligned_zeropad()

 arch/arm/include/asm/word-at-a-time.h              |  7 +++++++
 arch/arm64/include/asm/word-at-a-time.h            |  7 +++++++
 arch/powerpc/include/asm/word-at-a-time.h          |  6 ++++++
 arch/riscv/include/asm/word-at-a-time.h            |  6 ++++++
 arch/s390/include/asm/word-at-a-time.h             |  6 ++++++
 arch/x86/include/asm/word-at-a-time.h              |  6 ++++++
 mm/kasan/kasan_test_c.c                            | 24 ++++++++++++++++++++++
 .../powerpc/primitives/linux/kasan-checks.h        |  3 +++
 .../powerpc/primitives/linux/kcsan-checks.h        |  3 +++
 9 files changed, 68 insertions(+)
---
base-commit: c03c1a14507dfaf8b856c2608f9ac216021fc222
change-id: 20261019-bug-word-at-a-time-zeropad-kasan-af2460466ee6

Best regards,
-- 
Qiliang Yuan <odys.yuan at gmail.com>