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[PATCH v4 14/16] x86/dumpstack/64: Handle faults when printing the "Stack:" part of an OOPS

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  [PATCH v4 14/16] x86/dumpstack/64: Handle faults when printing the "Stack:" part of an OOPS Andy Lutomirski <luto@kernel.org> - 2016-06-24 06:30 +0200
    Re: [PATCH v4 14/16] x86/dumpstack/64: Handle faults when printing  the "Stack:" part of an OOPS Josh Poimboeuf <jpoimboe@redhat.com> - 2016-06-24 17:40 +0200

#1430343 — [PATCH v4 14/16] x86/dumpstack/64: Handle faults when printing the "Stack:" part of an OOPS

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 a81e1ef73bf2..6dede08dd98b 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -274,6 +274,8 @@ 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]);
@@ -283,12 +285,18 @@ 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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#1430759 — Re: [PATCH v4 14/16] x86/dumpstack/64: Handle faults when printing the "Stack:" part of an OOPS

On Thu, Jun 23, 2016 at 09:23:09PM -0700, Andy Lutomirski wrote:
> 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>

Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>

-- 
Josh

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