On Wed, Dec 23, 2020 at 2:57 AM Chang S. Bae [off-list ref] wrote:

The kernel pushes data on the userspace stack when entering a signal. If
using a sigaltstack(), the kernel precisely knows the user stack size.

When the kernel knows that the user stack is too small, avoid the overflow
and do an immediate SIGSEGV instead.

This overflow is known to occur on systems with large XSAVE state. The
effort to increase the size typically used for altstacks reduces the
frequency of these overflows, but this approach is still useful for legacy
binaries.

Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Chang S. Bae <redacted>
Reviewed-by: Len Brown <redacted>
Cc: Jann Horn <jannh@google.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org

Reviewed-by: Jann Horn <jannh@google.com>