[Devel] [PATCH RHEL7 COMMIT] ms/x86, mm, perf: Allow recursive faults from interrupts

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-957.1.3.vz7.83.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-957.1.3.vz7.83.9
------>
commit f5b3392f5e10bf73e41111fe6c9ac62b62a35449
Author: Peter Zijlstra <peterz at infradead.org>
Date:   Fri Feb 1 12:59:24 2019 +0300

    ms/x86, mm, perf: Allow recursive faults from interrupts
    
    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)
    https://jira.sw.ru/browse/PSBM-91181
    
    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;
 	}