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SubjectRe: [PATCH 3/3] x86/mm, tracing: Fix CR2 corruption
On Wed, Jul 03, 2019 at 12:27:34PM +0200, root wrote:
> Despire the current efforts to read CR2 before tracing happens there
> still exist a number of possible holes:
>
> idtentry page_fault do_page_fault has_error_code=1
> call error_entry
> TRACE_IRQS_OFF
> call trace_hardirqs_off*
> #PF // modifies CR2
>
> CALL_enter_from_user_mode
> __context_tracking_exit()
> trace_user_exit(0)
> #PF // modifies CR2
>
> call do_page_fault
> address = read_cr2(); /* whoopsie */
>
> And similar for i386.
>
> Fix it by pulling the CR2 read into the entry code, before any of that
> stuff gets a chance to run and ruin things.
>
> Ideally we'll clean up the entry code by moving this tracing and
> context tracking nonsense into C some day, but let's not delay fixing
> this longer.
>

> @@ -1180,10 +1189,10 @@ idtentry xenint3 do_int3 has_error_co
> #endif
>
> idtentry general_protection do_general_protection has_error_code=1
> -idtentry page_fault do_page_fault has_error_code=1
> +idtentry page_fault do_page_fault has_error_code=1 read_cr2=1
>
> #ifdef CONFIG_KVM_GUEST
> -idtentry async_page_fault do_async_page_fault has_error_code=1
> +idtentry async_page_fault do_async_page_fault has_error_code=1 read_cr2=1
> #endif

While going over the various idt handlers, I found that we probably also
need read_cr2 on do_double_fault(), otherwise it is susceptible to the
same problem.


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