In the Linux kernel, the following vulnerability has been resolved:

x86/signal: Detect and prevent an alternate signal stack overflow

The kernel pushes context on to the userspace stack to prepare for the
user's signal handler. When the user has supplied an alternate signal
stack, via sigaltstack(2), it is easy for the kernel to verify that the
stack size is sufficient for the current hardware context.

Check if writing the hardware context to the alternate stack will exceed
it's size. If yes, then instead of corrupting user-data and proceeding with
the original signal handler, an immediate SIGSEGV signal is delivered.

Refactor the stack pointer check code from on_sig_stack() and use the new
helper.

While the kernel allows new source code to discover and use a sufficient
alternate signal stack size, this check is still necessary to protect
binaries with insufficient alternate signal stack size from data
corruption.

References:
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-47326
https://www.cve.org/CVERecord?id=CVE-2021-47326
https://git.kernel.org/stable/c/00fcd8f33e9b9f57115c3b1cfc4cb96450c18796
https://git.kernel.org/stable/c/2beb4a53fc3f1081cedc1c1a198c7f56cc4fc60c
https://git.kernel.org/stable/c/74569cb9ed7bc60e395927f55d3dc3be143a0164
https://git.kernel.org/stable/c/74d6fcea1d896800e60f1c675137efebd1a6c9a6
https://git.kernel.org/stable/c/afb04d0b5543a5bf8e157b9119fbfc52606f4c11
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2021/CVE-2021-47326.mbox