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Date: Thu, 16 Jun 2016 13:16:42 -0500
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: Andy Lutomirski <luto@...nel.org>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
x86@...nel.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>
Subject: Re: [PATCH 10/13] x86/dumpstack: Try harder to get a call trace on
stack overflow
On Wed, Jun 15, 2016 at 05:28:32PM -0700, Andy Lutomirski wrote:
> If we overflow the stack, print_context_stack will abort. Detect
> this case and rewind back into the valid part of the stack so that
> we can trace it.
>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
> arch/x86/kernel/dumpstack.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index d4d085e27d04..400a2e17c1d1 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -100,6 +100,13 @@ print_context_stack(struct thread_info *tinfo,
> {
> struct stack_frame *frame = (struct stack_frame *)bp;
>
> + /*
> + * If we overflowed the stack into a guard page, jump back to the
> + * bottom of the usable stack.
> + */
> + if ((unsigned long)tinfo - (unsigned long)stack < PAGE_SIZE)
> + stack = (unsigned long *)tinfo + 1;
That will start walking the stack in the middle of the thread_info
struct.
I think you meant:
stack = (unsigned long *)(tinfo + 1)
However, thread_info will have been overwritten anyway. So maybe it
should just be:
stack = tinfo;
(Though that still wouldn't quite work because the valid_stack_ptr()
check would fail...)
> +
> while (valid_stack_ptr(tinfo, stack, sizeof(*stack), end)) {
> unsigned long addr;
--
Josh
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