x86: __memcpy_flushcache: fix wrong alignment if size > 2^32
authorMikulas Patocka <mpatocka@redhat.com>
Tue, 19 Apr 2022 13:56:23 +0000 (09:56 -0400)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 20 Apr 2022 18:38:49 +0000 (11:38 -0700)
commita6823e4e360fe975bd3da4ab156df7c74c8b07f3
tree0fdd5dfb998a6ca316ba4bcb7d89e94044ce29be
parent559089e0a93d44280ec3ab478830af319c56dbe3
x86: __memcpy_flushcache: fix wrong alignment if size > 2^32

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>
arch/x86/lib/usercopy_64.c