On Feb 9, 2023, at 3:19 AM, Sasha Levin sashal@kernel.org wrote:
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From: Vasily Gorbik gor@linux.ibm.com
[ Upstream commit 7ab41c2c08a32132ba8c14624910e2fe8ce4ba4b ]
Historically calls to __decompress() didn't specify "out_len" parameter on many architectures including s390, expecting that no writes beyond uncompressed kernel image are performed. This has changed since commit 2aa14b1ab2c4 ("zstd: import usptream v1.5.2") which includes zstd library commit 6a7ede3dfccb ("Reduce size of dctx by reutilizing dst buffer (#2751)"). Now zstd decompression code might store literal buffer in the unwritten portion of the destination buffer. Since "out_len" is not set, it is considered to be unlimited and hence free to use for optimization needs. On s390 this might corrupt initrd or ipl report which are often placed right after the decompressor buffer. Luckily the size of uncompressed kernel image is already known to the decompressor, so to avoid the problem simply specify it in the "out_len" parameter.
Thanks for the CC!
Reviewed-by: Nick Terrell <terrelln@fb. mailto:terrelln@fb.comcom>
It looks like s390 doesn't use in-place decompression, but x86 does, and we'll need to backport upstream commit 5b266196a [0] to make sure we don't overwrite the input buffer.
Best, Nick Terrell
[0] https://github.com/facebook/zstd/commit/5b266196a41e6a15e21bd4f0eeab43b938db...
Link: https://github.com/facebook/zstd/commit/6a7ede3dfccb Signed-off-by: Vasily Gorbik gor@linux.ibm.com Tested-by: Alexander Egorenkov egorenar@linux.ibm.com Link: https://lore.kernel.org/r/patch-1.thread-41c676.git-41c676c2d153.your-ad-her... Signed-off-by: Heiko Carstens hca@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org
arch/s390/boot/compressed/decompressor.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/s390/boot/compressed/decompressor.c b/arch/s390/boot/compressed/decompressor.c index 45046630c56ac..c42ab33bd4524 100644 --- a/arch/s390/boot/compressed/decompressor.c +++ b/arch/s390/boot/compressed/decompressor.c @@ -80,6 +80,6 @@ void *decompress_kernel(void) void *output = (void *)decompress_offset;
__decompress(_compressed_start, _compressed_end - _compressed_start,
NULL, NULL, output, 0, NULL, error);
NULL, NULL, output, vmlinux.image_size, NULL, error);return output; } -- 2.39.0