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== Background == As feature positions in the userspace XSAVE buffer do not always align with their feature numbers, the XSAVE format conversion needs to be reconsidered to align with the revised xstate size calculation logic. * For signal handling, XSAVE and XRSTOR are used directly to save and restore extended registers. * For ptrace, KVM, and signal returns (for 32-bit frame), the kernel copies data between its internal buffer and the userspace XSAVE buffer. If memcpy() were used for these cases, existing offset helpers — such as __raw_xsave_addr() or xstate_offsets[] — would be sufficient to handle the format conversion. == Problem == When copying data from the compacted in-kernel buffer to the non-compacted userspace buffer, the function follows the user_regset_get2_fn() prototype. This means it utilizes struct membuf helpers for the destination buffer. As defined in regset.h, these helpers update the memory pointer during the copy process, enforcing sequential writes within the loop. Since xstate components are processed sequentially, any component whose buffer position does not align with its feature number has an issue. == Solution == Replace for_each_extended_xfeature() with the newly introduced for_each_extended_xfeature_in_order(). This macro ensures xstate components are handled in the correct order based on their actual positions in the destination buffer, rather than their feature numbers. Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Oleg Nesterov <oleg@redhat.com> Link: https://lore.kernel.org/r/20250320234301.8342-5-chang.seok.bae@intel.com |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.