[v4,11/29] x86/dumpstack: When OOPSing, rewind the stack before do_exit
diff mbox

Message ID b05602fd545f3ddbb2c3e2bfd2ef5d18e85edd50.1466974736.git.luto@kernel.org
State New
Headers show

Commit Message

Andy Lutomirski June 26, 2016, 9:55 p.m. UTC
If we call do_exit with a clean stack, we greatly reduce the risk of
recursive oopses due to stack overflow in do_exit, and we allow
do_exit to work even if we OOPS from an IST stack.  The latter gives
us a much better chance of surviving long enough after we detect a
stack overflow to write out our logs.

I intentionally separated this from the preceding patch that
disables do_exit-on-OOPS on IST stacks.  This way, if we need to
revert this patch, we still end up in an acceptable state wrt stack
overflow handling.

Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/entry/entry_32.S   | 11 +++++++++++
 arch/x86/entry/entry_64.S   | 11 +++++++++++
 arch/x86/kernel/dumpstack.c | 13 +++++++++----
 3 files changed, 31 insertions(+), 4 deletions(-)

Comments

Borislav Petkov July 4, 2016, 6:45 p.m. UTC | #1
On Sun, Jun 26, 2016 at 02:55:33PM -0700, Andy Lutomirski wrote:
> If we call do_exit with a clean stack, we greatly reduce the risk of

Nits:	    do_exit()

> recursive oopses due to stack overflow in do_exit, and we allow

s/ in do_exit//

> do_exit to work even if we OOPS from an IST stack.  The latter gives

Append "()" to the function names.

> us a much better chance of surviving long enough after we detect a
> stack overflow to write out our logs.
> 
> I intentionally separated this from the preceding patch that
> disables do_exit-on-OOPS on IST stacks.  This way, if we need to
> revert this patch, we still end up in an acceptable state wrt stack
> overflow handling.
> 
> Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---

...

> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index 352f022cfd5b..0d05f113805e 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -226,6 +226,8 @@ unsigned long oops_begin(void)
>  EXPORT_SYMBOL_GPL(oops_begin);
>  NOKPROBE_SYMBOL(oops_begin);
>  
> +extern void __noreturn rewind_stack_do_exit(int signr);

You don't need the "extern" here.

> +
>  void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
>  {
>  	if (regs && kexec_should_crash(current))

Patch
diff mbox

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 983e5d3a0d27..0b56666e6039 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -1153,3 +1153,14 @@  ENTRY(async_page_fault)
 	jmp	error_code
 END(async_page_fault)
 #endif
+
+ENTRY(rewind_stack_do_exit)
+	/* Prevent any naive code from trying to unwind to our caller. */
+	xorl	%ebp, %ebp
+
+	movl	PER_CPU_VAR(cpu_current_top_of_stack), %esi
+	leal	-TOP_OF_KERNEL_STACK_PADDING-PTREGS_SIZE(%esi), %esp
+
+	call	do_exit
+1:	jmp 1b
+END(rewind_stack_do_exit)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 9ee0da1807ed..b846875aeea6 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1423,3 +1423,14 @@  ENTRY(ignore_sysret)
 	mov	$-ENOSYS, %eax
 	sysret
 END(ignore_sysret)
+
+ENTRY(rewind_stack_do_exit)
+	/* Prevent any naive code from trying to unwind to our caller. */
+	xorl	%ebp, %ebp
+
+	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rax
+	leaq	-TOP_OF_KERNEL_STACK_PADDING-PTREGS_SIZE(%rax), %rsp
+
+	call	do_exit
+1:	jmp 1b
+END(rewind_stack_do_exit)
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 352f022cfd5b..0d05f113805e 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -226,6 +226,8 @@  unsigned long oops_begin(void)
 EXPORT_SYMBOL_GPL(oops_begin);
 NOKPROBE_SYMBOL(oops_begin);
 
+extern void __noreturn rewind_stack_do_exit(int signr);
+
 void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
 {
 	if (regs && kexec_should_crash(current))
@@ -245,12 +247,15 @@  void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
 		return;
 	if (in_interrupt())
 		panic("Fatal exception in interrupt");
-	if (((current_stack_pointer() ^ (current_top_of_stack() - 1))
-	     & ~(THREAD_SIZE - 1)) != 0)
-		panic("Fatal exception on special stack");
 	if (panic_on_oops)
 		panic("Fatal exception");
-	do_exit(signr);
+
+	/*
+	 * We're not going to return, but we might be on an IST stack or
+	 * have very little stack space left.  Rewind the stack and kill
+	 * the task.
+	 */
+	rewind_stack_do_exit(signr);
 }
 NOKPROBE_SYMBOL(oops_end);