On Wed, Feb 21, 2024 at 09:29:08PM +0100, Thomas Gleixner wrote:
From: Andrei Vagin avagin@google.com
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:
- fx_sw->xstate_size is smaller than the size required by valid bits in fx_sw->xfeatures.
- user-space unmaps parts of the sigrame fpu buffer so that not all of the buffer required by xrstor is accessible.
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 ] [ tglx: Backport to 5.15 stable ]
Fixes: fcb3635f5018 ("x86/fpu/signal: Handle #PF in the direct restore path") Reported-by: Konstantin Bogomolov bogomolov@google.com Suggested-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Andrei Vagin avagin@google.com Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Link: https://lore.kernel.org/all/20240130063603.3392627-1-avagin%40google.com
arch/x86/kernel/fpu/signal.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)
Nit, you forgot to give me a hint what the git id was :(
I figured it out, now queued up, thanks.
greg k-h