[PATCH 6.1 058/197] powerpc/kasan: Fix addr error caused by page alignment

Greg Kroah-Hartman
2024-02-20T21:00:57Z

From: Jiangfeng Xiao <xiaojiangfeng@huawei.com>

[ Upstream commit 4a7aee96200ad281a5cc4cf5c7a2e2a49d2b97b0 ]

In kasan_init_region, when k_start is not page aligned, at the begin of
for loop, k_cur = k_start & PAGE_MASK is less than k_start, and then
`va = block + k_cur - k_start` is less than block, the addr va is invalid,
because the memory address space from va to block is not alloced by
memblock_alloc, which will not be reserved by memblock_reserve later, it
will be used by other places.

As a result, memory overwriting occurs.

for example:
int __init __weak kasan_init_region(void *start, size_t size)
{
[...]
/* if say block(dcd97000) k_start(feef7400) k_end(feeff3fe) */
block = memblock_alloc(k_end - k_start, PAGE_SIZE);
[...]
for (k_cur = k_start & PAGE_MASK; k_cur < k_end; k_cur += PAGE_SIZE) {
/* at the begin of for loop
* block(dcd97000) va(dcd96c00) k_cur(feef7000) k_start(feef7400)
* va(dcd96c00) is less than block(dcd97000), va is invalid
*/
void *va = block + k_cur - k_start;
[...]
}
[...]
}

Therefore, page alignment is performed on k_start before
memblock_alloc() to ensure the validity of the VA address.

Fixes: 663c0c9496a6 ("powerpc/kasan: Fix shadow area set up for modules.")
Signed-off-by: Jiangfeng Xiao <xiaojiangfeng@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/1705974359-43790-1-git-send-email-xiaojiangfeng@huawei.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/mm/kasan/init_32.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/mm/kasan/init_32.c b/arch/powerpc/mm/kasan/init_32.c
index a70828a6d935..aa9aa11927b2 100644
--- a/arch/powerpc/mm/kasan/init_32.c
+++ b/arch/powerpc/mm/kasan/init_32.c
@@ -64,6 +64,7 @@ int __init __weak kasan_init_region(void *start, size_t size)
if (ret)
return ret;

+ k_start = k_start & PAGE_MASK;
block = memblock_alloc(k_end - k_start, PAGE_SIZE);
if (!block)
return -ENOMEM;
--
2.43.0