linux-kernel - [PATCH v3 04/10] x86/dumpstack: fix interrupt and exception stack boundary checks

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Message-Id: <bcc142160a5104de5c354c21c394c93a0173943f.1499786555.git.jpoimboe@redhat.com>
Date:   Tue, 11 Jul 2017 10:33:41 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>, Jiri Slaby <jslaby@...e.cz>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mike Galbraith <efault@....de>
Subject: [PATCH v3 04/10] x86/dumpstack: fix interrupt and exception stack boundary checks

On x86_64, the double fault exception stack is located immediately after
the interrupt stack in memory.  This causes confusion in the unwinder
when it tries to unwind through an empty interrupt stack, where the
stack pointer points to the address bordering the two stacks.  The
unwinder incorrectly thinks it's running on the double fault stack.

Fix this kind of stack border confusion by never considering the
beginning address of an exception or interrupt stack to be part of the
stack.

Fixes: 5fe599e02e41 ("x86/dumpstack: Add support for unwinding empty IRQ stacks")
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/kernel/dumpstack_32.c | 4 ++--
 arch/x86/kernel/dumpstack_64.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index e5f0b40..4f04814 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -37,7 +37,7 @@ static bool in_hardirq_stack(unsigned long *stack, struct stack_info *info)
 	 * This is a software stack, so 'end' can be a valid stack pointer.
 	 * It just means the stack is empty.
 	 */
-	if (stack < begin || stack > end)
+	if (stack <= begin || stack > end)
 		return false;
 
 	info->type	= STACK_TYPE_IRQ;
@@ -62,7 +62,7 @@ static bool in_softirq_stack(unsigned long *stack, struct stack_info *info)
 	 * This is a software stack, so 'end' can be a valid stack pointer.
 	 * It just means the stack is empty.
 	 */
-	if (stack < begin || stack > end)
+	if (stack <= begin || stack > end)
 		return false;
 
 	info->type	= STACK_TYPE_SOFTIRQ;
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 3e1471d..225af41 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -55,7 +55,7 @@ static bool in_exception_stack(unsigned long *stack, struct stack_info *info)
 		begin = end - (exception_stack_sizes[k] / sizeof(long));
 		regs  = (struct pt_regs *)end - 1;
 
-		if (stack < begin || stack >= end)
+		if (stack <= begin || stack >= end)
 			continue;
 
 		info->type	= STACK_TYPE_EXCEPTION + k;
@@ -78,7 +78,7 @@ static bool in_irq_stack(unsigned long *stack, struct stack_info *info)
 	 * This is a software stack, so 'end' can be a valid stack pointer.
 	 * It just means the stack is empty.
 	 */
-	if (stack < begin || stack > end)
+	if (stack <= begin || stack > end)
 		return false;
 
 	info->type	= STACK_TYPE_IRQ;
-- 
2.7.5