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

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Message-Id: <bdb80a7119a4045a7c7d78218d14100b027ed1f6.1466192946.git.luto@kernel.org>
Date:	Fri, 17 Jun 2016 13:00:47 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org, linux-kernel@...r.kernel.org
Cc:	linux-arch@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
	Nadav Amit <nadav.amit@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Jann Horn <jann@...jh.net>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v2 11/13] 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@...nel.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