On Fri Sep 27, 2024 at 3:23 PM BST, Alejandro Vallejo wrote:
> Hitting a page fault clobbers %cr2, so if a page fault is handled while
> handling a previous page fault then %cr2 will hold the address of the
> latter fault rather than the former. This patch makes the page fault
> path delay re-enabling IRQs until %cr2 has been read in order to ensure
> it stays consistent.
>
> A similar argument holds in additional cases, but they happen to be safe:
>
> * %dr6 inside #DB: Safe because IST exceptions don't re-enable IRQs.
> * MSR_XFD_ERR inside #NM: Safe because AMX isn't used in #NM handler.
>
> While in the area, remove redundant q suffix to a movq in entry.S and
> add space after the comma.
>
> Fixes: a4cd20a19073 ("[XEN] 'd' key dumps both host and guest state.")
> Signed-off-by: Alejandro Vallejo <[email protected]>
> Acked-by: Roger Pau Monné <[email protected]>
> ---
> v3:
> * s/dispatch_handlers/dispatch_exceptions/
> * Updated commit message, spelling out the state of #DB and #NM, and
> state an existing race with debug keys.
Bah, I didn't refresh the patch with the latest commit message. It was meant to
be:
x86/traps: Re-enable interrupts after reading cr2 in the #PF handler
Hitting a page fault clobbers %cr2, so if a page fault is handled while
handling a previous page fault then %cr2 will hold the address of the latter
fault rather than the former. In particular, if a debug key handler happens
to trigger during #PF and before %cr2 is read, and that handler itself
encounters a #PF, then %cr2 will be corrupt for the outer #PF handler.
This patch makes the page fault path delay re-enabling IRQs until %cr2 has
been read in order to ensure it stays consistent.
A similar argument holds in additional cases, but they happen to be safe:
* %dr6 inside #DB: Safe because IST exceptions don't re-enable IRQs.
* MSR_XFD_ERR inside #NM: Safe because AMX isn't used in #NM handler.
While in the area, remove redundant q suffix to a movq in entry.S and
add space after the comma.
Fixes: a4cd20a19073 ("[XEN] 'd' key dumps both host and guest state.")
Signed-off-by: Alejandro Vallejo <[email protected]>
Acked-by: Roger Pau Monné <[email protected]>
Would whoever planned to commit this mind replacing the commit msg on commit?
Otherwise I'll just resend.
Cheers,
Alejandro
