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

[Andy Lutomirski]

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 <l...@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