[PATCH 5.4 70/84] x86: __memcpy_flushcache: fix wrong alignment if size > 2^32

Greg Kroah-Hartman
2022-05-04T16:52:42Z

From: Mikulas Patocka <mpatocka@redhat.com>

[ Upstream commit a6823e4e360fe975bd3da4ab156df7c74c8b07f3 ]

The first "if" condition in __memcpy_flushcache is supposed to align the
"dest" variable to 8 bytes and copy data up to this alignment. However,
this condition may misbehave if "size" is greater than 4GiB.

The statement min_t(unsigned, size, ALIGN(dest, 8) - dest); casts both
arguments to unsigned int and selects the smaller one. However, the
cast truncates high bits in "size" and it results in misbehavior.

For example:

suppose that size == 0x100000001, dest == 0x200000002
min_t(unsigned, size, ALIGN(dest, 8) - dest) == min_t(0x1, 0xe) == 0x1;
...
dest += 0x1;

so we copy just one byte "and" dest remains unaligned.

This patch fixes the bug by replacing unsigned with size_t.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/lib/usercopy_64.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 1847e993ac63..f3f7f4cb15a6 100644
--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -142,7 +142,7 @@ void __memcpy_flushcache(void *_dst, const void *_src, size_t size)

/* cache copy and flush to align dest */
if (!IS_ALIGNED(dest, 8)) {
- unsigned len = min_t(unsigned, size, ALIGN(dest, 8) - dest);
+ size_t len = min_t(size_t, size, ALIGN(dest, 8) - dest);

memcpy((void *) dest, (void *) source, len);
clean_cache_range((void *) dest, len);
--
2.35.1