From: Gao Xiang <hsiangkao@xxxxxxxxxx> commit 89b158635ad79574bde8e94d45dad33f8cf09549 upstream. LZ4 final literal copy could be overlapped when doing in-place decompression, so it's unsafe to just use memcpy() on an optimized memcpy approach but memmove() instead. Upstream LZ4 has updated this years ago [1] (and the impact is non-sensible [2] plus only a few bytes remain), this commit just synchronizes LZ4 upstream code to the kernel side as well. It can be observed as EROFS in-place decompression failure on specific files when X86_FEATURE_ERMS is unsupported, memcpy() optimization of commit 59daa706fbec ("x86, mem: Optimize memcpy by avoiding memory false dependece") will be enabled then. Currently most modern x86-CPUs support ERMS, these CPUs just use "rep movsb" approach so no problem at all. However, it can still be verified with forcely disabling ERMS feature... arch/x86/lib/memcpy_64.S: ALTERNATIVE_2 "jmp memcpy_orig", "", X86_FEATURE_REP_GOOD, \ - "jmp memcpy_erms", X86_FEATURE_ERMS + "jmp memcpy_orig", X86_FEATURE_ERMS We didn't observe any strange on arm64/arm/x86 platform before since most memcpy() would behave in an increasing address order ("copy upwards" [3]) and it's the correct order of in-place decompression but it really needs an update to memmove() for sure considering it's an undefined behavior according to the standard and some unique optimization already exists in the kernel. [1] https://github.com/lz4/lz4/commit/33cb8518ac385835cc17be9a770b27b40cd0e15b [2] https://github.com/lz4/lz4/pull/717#issuecomment-497818921 [3] https://sourceware.org/bugzilla/show_bug.cgi?id=12518 Link: https://lkml.kernel.org/r/20201122030749.2698994-1-hsiangkao@xxxxxxxxxx Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxx> Reviewed-by: Nick Terrell <terrelln@xxxxxx> Cc: Yann Collet <yann.collet.73@xxxxxxxxx> Cc: Miao Xie <miaoxie@xxxxxxxxxx> Cc: Chao Yu <yuchao0@xxxxxxxxxx> Cc: Li Guifu <bluce.liguifu@xxxxxxxxxx> Cc: Guo Xuenan <guoxuenan@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- lib/lz4/lz4_decompress.c | 6 +++++- lib/lz4/lz4defs.h | 2 ++ 2 files changed, 7 insertions(+), 1 deletion(-) --- a/lib/lz4/lz4_decompress.c +++ b/lib/lz4/lz4_decompress.c @@ -260,7 +260,11 @@ static FORCE_INLINE int LZ4_decompress_g } } - memcpy(op, ip, length); + /* + * supports overlapping memory regions; only matters + * for in-place decompression scenarios + */ + LZ4_memmove(op, ip, length); ip += length; op += length; --- a/lib/lz4/lz4defs.h +++ b/lib/lz4/lz4defs.h @@ -137,6 +137,8 @@ static FORCE_INLINE void LZ4_writeLE16(v return put_unaligned_le16(value, memPtr); } +#define LZ4_memmove(dst, src, size) __builtin_memmove(dst, src, size) + static FORCE_INLINE void LZ4_copy8(void *dst, const void *src) { #if LZ4_ARCH64