In the Linux kernel, the following vulnerability has been resolved:
x86/fpu: Stop relying on userspace for info to fault in xsave buffer
Before this change, the expected size of the user space buffer was
taken from fx_sw->xstate_size. fx_sw->xstate_size can be changed
from user-space, so it is possible construct a sigreturn frame where:
In this case, xrstor tries to restore and accesses the unmapped area
which results in a fault. But fault_in_readable succeeds because buf +
fx_sw->xstate_size is within the still mapped area, so it goes back and
tries xrstor again. It will spin in this loop forever.
Instead, fault in the maximum size which can be touched by XRSTOR (taken
from fpstate->user_size).
[ dhansen: tweak subject / changelog ]
git.kernel.org/stable/c/627339cccdc9166792ecf96bc3c9f711a60ce996
git.kernel.org/stable/c/627e28cbb65564e55008315d9e02fbb90478beda
git.kernel.org/stable/c/8bd3eee7720c14b59a206bd05b98d7586bccf99a
git.kernel.org/stable/c/b2479ab426cef7ab79a13005650eff956223ced2
git.kernel.org/stable/c/d877550eaf2dc9090d782864c96939397a3c6835