[Devel] [PATCH rh7] x86, mm, perf: Allow recursive faults from interrupts

[Andrey Ryabinin]

This is RK-worthy, please consider.


On 1/24/19 6:44 PM, Andrey Ryabinin wrote:
> From: Peter Zijlstra <peterz at infradead.org>
> 
> Waiman managed to trigger a PMI while in a emulate_vsyscall() fault,
> the PMI in turn managed to trigger a fault while obtaining a stack
> trace. This triggered the sig_on_uaccess_error recursive fault logic
> and killed the process dead.
> 
> Fix this by explicitly excluding interrupts from the recursive fault
> logic.
> 
> Reported-and-Tested-by: Waiman Long <waiman.long at hp.com>
> Fixes: e00b12e64be9 ("perf/x86: Further optimize copy_from_user_nmi()")
> Cc: Aswin Chandramouleeswaran <aswin at hp.com>
> Cc: Scott J Norton <scott.norton at hp.com>
> Cc: Linus Torvalds <torvalds at linux-foundation.org>
> Cc: Andy Lutomirski <luto at amacapital.net>
> Cc: Arnaldo Carvalho de Melo <acme at ghostprotocols.net>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Peter Zijlstra <peterz at infradead.org>
> Link: http://lkml.kernel.org/r/20140110200603.GJ7572@laptop.programming.kicks-ass.net
> Signed-off-by: Ingo Molnar <mingo at kernel.org>
> (cherry picked from commit c026b3591e4f2a4993df773183704bb31634e0bd)
> Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
> ---
>  arch/x86/mm/fault.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 0e41582126a9..5a8f2cf83164 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -687,6 +687,20 @@ no_context(struct pt_regs *regs, unsigned long error_code,
>  
>  	/* Are we prepared to handle this kernel fault? */
>  	if (fixup_exception(regs)) {
> +		/*
> +		 * Any interrupt that takes a fault gets the fixup. This makes
> +		 * the below recursive fault logic only apply to a faults from
> +		 * task context.
> +		 */
> +		if (in_interrupt())
> +			return;
> +
> +		/*
> +		 * Per the above we're !in_interrupt(), aka. task context.
> +		 *
> +		 * In this case we need to make sure we're not recursively
> +		 * faulting through the emulate_vsyscall() logic.
> +		 */
>  		if (current_thread_info()->sig_on_uaccess_error && signal) {
>  			tsk->thread.trap_nr = X86_TRAP_PF;
>  			tsk->thread.error_code = error_code | X86_PF_USER;
> @@ -696,6 +710,10 @@ no_context(struct pt_regs *regs, unsigned long error_code,
>  			force_sig_info_fault(signal, si_code, address,
>  					     tsk, vma, 0);
>  		}
> +
> +		/*
> +		 * Barring that, we can do the fixup and be happy.
> +		 */
>  		return;
>  	}
>  
>