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x86/mm: Fix overflow in __cpa_addr()

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The change to have cpa_flush() call flush_kernel_pages() introduced
a bug where __cpa_addr() can access an address one larger than the
largest one in the cpa->pages array.

KASAN reports the issue like this:

BUG: KASAN: slab-out-of-bounds in __cpa_addr arch/x86/mm/pat/set_memory.c:309 [inline]
BUG: KASAN: slab-out-of-bounds in __cpa_addr+0x1d3/0x220 arch/x86/mm/pat/set_memory.c:306
Read of size 8 at addr ffff88801f75e8f8 by task syz.0.17/5978

This bug could cause cpa_flush() to not properly flush memory,
which somehow never showed any symptoms in my tests, possibly
because cpa_flush() is called so rarely, but could potentially
cause issues for other people.

Fix the issue by directly calculating the flush end address
from the start address.

Fixes: 86e6815b31 ("x86/mm: Change cpa_flush() to call flush_kernel_range() directly")
Reported-by: syzbot+afec6555eef563c66c97@syzkaller.appspotmail.com
Signed-off-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Kiryl Shutsemau <kas@kernel.org>
Link: https://lore.kernel.org/all/68e2ff90.050a0220.2c17c1.0038.GAE@google.com/
This commit is contained in:
Rik van Riel 2025-10-05 23:48:05 -04:00 committed by Dave Hansen
parent 15292f1b4c
commit f25785f9b0
1 changed files with 1 additions and 1 deletions
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2
arch/x86/mm/pat/set_memory.c
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@ -446,7 +446,7 @@ static void cpa_flush(struct cpa_data *cpa, int cache)
}
start = fix_addr(__cpa_addr(cpa, 0));
end = fix_addr(__cpa_addr(cpa, cpa->numpages));
end = start + cpa->numpages * PAGE_SIZE;
if (cpa->force_flush_all)
end = TLB_FLUSH_ALL;