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[PATCH v2 11/13] x86/dumpstack/64: Handle faults when printing the "Stack:" part of an OOPS

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If we overflow the stack into a guard page, we'll recursively fault
when trying to dump the contents of the guard page.  Use
probe_kernel_address so we can recover if this happens.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/kernel/dumpstack_64.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 603356a5597a..5e298638c790 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -276,6 +276,8 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
 
 	stack = sp;
 	for (i = 0; i < kstack_depth_to_print; i++) {
+		unsigned long word;
+
 		if (stack >= irq_stack && stack <= irq_stack_end) {
 			if (stack == irq_stack_end) {
 				stack = (unsigned long *) (irq_stack_end[-1]);
@@ -285,12 +287,18 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
 		if (kstack_end(stack))
 			break;
 		}
+
+		if (probe_kernel_address(stack, word))
+			break;
+
 		if ((i % STACKSLOTS_PER_LINE) == 0) {
 			if (i != 0)
 				pr_cont("\n");
-			printk("%s %016lx", log_lvl, *stack++);
+			printk("%s %016lx", log_lvl, word);
 		} else
-			pr_cont(" %016lx", *stack++);
+			pr_cont(" %016lx", word);
+
+		stack++;
 		touch_nmi_watchdog();
 	}
 	preempt_enable();
-- 
2.5.5

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[PATCH v2 00/13] Virtually mapped stacks with guard pages (x86, core) Andy Lutomirski <luto@kernel.org> - 2016-06-17 22:10 +0200
  [PATCH v2 13/13] x86/mm: Improve stack-overflow #PF handling Andy Lutomirski <luto@kernel.org> - 2016-06-17 22:10 +0200
  [PATCH v2 11/13] x86/dumpstack/64: Handle faults when printing the "Stack:" part of an OOPS Andy Lutomirski <luto@kernel.org> - 2016-06-17 22:10 +0200
  [PATCH v2 07/13] x86/die: Don't try to recover from an OOPS on a non-default stack Andy Lutomirski <luto@kernel.org> - 2016-06-17 22:10 +0200
  [PATCH v2 01/13] x86/mm/hotplug: Don't remove PGD entries in remove_pagetable() Andy Lutomirski <luto@kernel.org> - 2016-06-17 22:10 +0200
  [PATCH v2 08/13] x86/dumpstack: When OOPSing, rewind the stack before do_exit Andy Lutomirski <luto@kernel.org> - 2016-06-17 22:10 +0200
  [PATCH v2 10/13] x86/dumpstack: Try harder to get a call trace on stack overflow Andy Lutomirski <luto@kernel.org> - 2016-06-17 22:10 +0200
  [PATCH v2 05/13] mm: Move memcg stack accounting to account_kernel_stack Andy Lutomirski <luto@kernel.org> - 2016-06-17 22:10 +0200
    Re: [PATCH v2 05/13] mm: Move memcg stack accounting to  account_kernel_stack Josh Poimboeuf <jpoimboe@redhat.com> - 2016-06-17 23:00 +0200
      Re: [PATCH v2 05/13] mm: Move memcg stack accounting to account_kernel_stack Andy Lutomirski <luto@amacapital.net> - 2016-06-18 00:20 +0200
    Re: [PATCH v2 05/13] mm: Move memcg stack accounting to  account_kernel_stack Michal Hocko <mhocko@kernel.org> - 2016-06-20 15:10 +0200
      Re: [PATCH v2 05/13] mm: Move memcg stack accounting to account_kernel_stack Andy Lutomirski <luto@amacapital.net> - 2016-06-20 18:10 +0200

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