This is *NOT* done for security reasons even though the backdoor
relied on the ifunc code. Instead, the reason is that in this
project ifunc provides little benefits but it's quite a bit of
extra code to support it. The only case where ifunc *might* matter
for performance is if the CRC functions are used directly by an
application. In normal compression use it's completely irrelevant.
While the backdoor was inactive (and thus harmless) without inserting
a small trigger code into the build system when the source package was
created, it's good to remove this anyway:
- The executable payloads were embedded as binary blobs in
the test files. This was a blatant violation of the
Debian Free Software Guidelines.
- On machines that see lots bots poking at the SSH port, the backdoor
noticeably increased CPU load, resulting in degraded user experience
and thus overwhelmingly negative user feedback.
- The maintainer who added the backdoor has disappeared.
- Backdoors are bad for security.
This reverts the following without making any other changes:
6e636819 Tests: Update two test files.
a3a29bbd Tests: Test --single-stream can decompress bad-3-corrupt_lzma2.xz.
0b4ccc91 Tests: Update RISC-V test files.
8c9b8b20 liblzma: Fix typos in crc32_fast.c and crc64_fast.c.
82ecc538 liblzma: Fix false Valgrind error report with GCC.
cf44e4b7 Tests: Add a few test files.
3060e107 Tests: Use smaller dictionary size in RISC-V test files.
e2870db5 Tests: Add two RISC-V Filter test files.
The RISC-V test files also have real content that tests the filter
but the real content would fit into much smaller files. A generator
program would need to be available as well.
Thanks to Andres Freund for finding and reporting it and making
it public quickly so others could act without a delay.
See: https://www.openwall.com/lists/oss-security/2024/03/29/4
NVHPC compiler has several issues that make it impossible to
build liblzma:
- the compiler cannot handle unions that contain pointers that
are not the first members;
- the compiler cannot handle the assembler code in range_decoder.h
(LZMA_RANGE_DECODER_CONFIG has to be set to zero);
- the compiler fails to produce valid code for delta_decode if the
vectorization is enabled, which results in failed tests.
This introduces NVHPC-specific workarounds that address the issues.
With GCC and a certain combination of flags, Valgrind will falsely
trigger an invalid write. This appears to be due to the omission of
instructions to properly save, set up, and restore the frame pointer.
The IFUNC resolver is a leaf function since it only calls a function
that is inlined. So sometimes GCC omits the frame pointer instructions
in the resolver unless this optimization is explictly disabled.
This fixes https://bugzilla.redhat.com/show_bug.cgi?id=2267598.
Like 5.5.0alpha, 5.7.0alpha won't be released, it's just to mark that
the branch is not stable.
Once again there is no API/ABI stability for new features in devel
versions. The major soname won't be bumped even if API/ABI of new
features breaks between devel releases.
GCC docs promise that it works and a few other compilers do
too. Clang/LLVM is documented source code only but unsurprisingly
it behaves the same as others on x86-64 at least. But the
certainly-portable way is good enough here so use that.
The x32 port has a x86-64 ABI in term of all registers but uses only
32bit pointer like x86-32. The assembly optimisation fails to compile on
x32. Given the state of x32 I suggest to exclude it from the
optimisation rather than trying to fix it.
Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
It's used only for basic bittrees and fixed-size reverse bittree
because those showed a clear benefit on x86-64 with GCC and Clang.
The other methods were more mixed and thus are commented out but
they should be tested on other archs.
Now extra buffer space is reserved so that repeating bytes for
any single match will never need to copy from two places (both
the beginning and the end of the buffer). This simplifies
dict_repeat() and helps a little with speed.
This seems to reduce .lzma decompression time about 2 %, so
with .xz and CRC it could be slightly less. The small things
add up still.
It's not completely obvious if this is better in the decoder.
It should be good if compiler can avoid creating a branch
(like using CMOV on x86).
This also makes lzma_encoder.c use the new macros.
The new decoder resumes the first decoder loop in the Resumable mode.
Then, the code executes in Non-resumable mode until it detects that it
cannot guarantee to have enough input/output to decode another symbol.
The Resumable mode is how the decoder has always worked. Before decoding
every input bit, it checks if there is enough space and will save its
location to be resumed later. When the decoder has more input/output,
it jumps back to the correct sequence in the Resumable mode code.
When the input/output buffers are large, the Resumable mode is much
slower than the Non-resumable because it has more branches and is harder
for the compiler to optimize since it is in a large switch block.
Early benchmarking shows significant time improvement (8-10% on gcc and
clang x86) by using the Non-resumable code as much as possible.
The new "safe" range decoder mode is the same as old range decoder, but
now the default behavior of the range decoder will not check if there is
enough input or output to complete the operation. When the buffers are
close to fully consumed, the "safe" operations must be used instead. This
will improve speed because it will reduce the number of branches needed
for most of the range decoder operations.
Perhaps the generated files aren't even copyrightable but
using the same license for them as for the rest of the liblzma
keeps things more consistent for tools that look for license info.
The initial commit 5d018dc035
in 2007 had a comment in sha256.c that the code is based on
Crypto++ Library 5.5.1. In 2009 the Authors list in sha256.c
and the AUTHORS file was updated with information that the
code had come from Crypto++ but via 7-Zip. I know I had viewed
7-Zip's SHA-256 code but back then the C code has been identical
enough with Crypto++, so I don't why I thought the author info
would need that extra step via 7-Zip for this single file.
Another error is that I had mixed sha.* and shacal2.* files
when checking for author info in Crypto++. The shacal2.* files
aren't related to liblzma's sha256.c and thus Kevin Springle's
code in Crypto++ isn't either.
If liblzma is configured with --disable-clmul-crc
CFLAGS="-msse4.1 -mpclmul", then it will fail to compile because the
generic version must be used but the CRC tables were not included.
The code was using HAVE_FUNC_ATTRIBUTE_IFUNC instead of CRC_USE_IFUNC.
With ARM64, ifunc is incompatible because it requires non-inline
function calls for runtime detection.
Lasse Collin
Sergey Kosukhin
Jia Tan
Sebastian Andrzej Siewior