[PATCH AUTOSEL 6.10 092/121] x86/kmsan: Fix hook for unaligned accesses

Sasha Levin
2024-08-01T00:17:02Z

From: Brian Johannesmeyer <bjohannesmeyer@gmail.com>

[ Upstream commit bf6ab33d8487f5e2a0998ce75286eae65bb0a6d6 ]

When called with a 'from' that is not 4-byte-aligned, string_memcpy_fromio()
calls the movs() macro to copy the first few bytes, so that 'from' becomes
4-byte-aligned before calling rep_movs(). This movs() macro modifies 'to', and
the subsequent line modifies 'n'.

As a result, on unaligned accesses, kmsan_unpoison_memory() uses the updated
(aligned) values of 'to' and 'n'. Hence, it does not unpoison the entire
region.

Save the original values of 'to' and 'n', and pass those to
kmsan_unpoison_memory(), so that the entire region is unpoisoned.

Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Alexander Potapenko <glider@google.com>
Link: https://lore.kernel.org/r/20240523215029.4160518-1-bjohannesmeyer@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/lib/iomem.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/lib/iomem.c b/arch/x86/lib/iomem.c
index e0411a3774d49..5eecb45d05d5d 100644
--- a/arch/x86/lib/iomem.c
+++ b/arch/x86/lib/iomem.c
@@ -25,6 +25,9 @@ static __always_inline void rep_movs(void *to, const void *from, size_t n)

static void string_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
{
+ const void *orig_to = to;
+ const size_t orig_n = n;
+
if (unlikely(!n))
return;

@@ -39,7 +42,7 @@ static void string_memcpy_fromio(void *to, const volatile void __iomem *from, si
}
rep_movs(to, (const void *)from, n);
/* KMSAN must treat values read from devices as initialized. */
- kmsan_unpoison_memory(to, n);
+ kmsan_unpoison_memory(orig_to, orig_n);
}

static void string_memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
--
2.43.0