[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20160616185446.rzlpbfeowsmzlqb4@treble>
Date: Thu, 16 Jun 2016 13:54:46 -0500
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: Andy Lutomirski <luto@...capital.net>
Cc: Andy Lutomirski <luto@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
X86 ML <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 Thu, Jun 16, 2016 at 11:37:07AM -0700, Andy Lutomirski wrote:
> On Thu, Jun 16, 2016 at 11:33 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > On Thu, Jun 16, 2016 at 11:22:14AM -0700, Andy Lutomirski wrote:
> >> On Thu, Jun 16, 2016 at 11:16 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >> > 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...)
> >>
> >> I did mean what I wrote, because I wanted to start at the bottom of
> >> the validly allocated area. IOW I wanted to do the minimum possible
> >> backward jump to make the code display something.
> >
> > But why the "+ 1"? Is that a hack to make it pass the valid_stack_ptr()
> > check?
>
> Yes.
>
> But hmm. Maybe the right fix is to drop the + 1 and to change the
> last line of valid_stck_ptr from:
>
> return p > t && p < t + THREAD_SIZE - size;
>
> to:
>
> return p >= t && p < t + THREAD_SIZE - size;
Yeah, I think that would be much better. Then it won't skip the first
value on the page.
--
Josh
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
