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Message-ID: <20170105203755.ai3ida5p2twwtvx6@treble>
Date: Thu, 5 Jan 2017 14:37:55 -0600
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: syzkaller <syzkaller@...glegroups.com>,
Andrey Konovalov <andreyknvl@...gle.com>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Alexander Potapenko <glider@...gle.com>,
kasan-dev <kasan-dev@...glegroups.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>,
"x86@...nel.org" <x86@...nel.org>,
Kostya Serebryany <kcc@...gle.com>
Subject: Re: x86: warning in unwind_get_return_address
On Thu, Jan 05, 2017 at 09:23:14PM +0100, Dmitry Vyukov wrote:
> On Thu, Jan 5, 2017 at 6:03 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > On Thu, Jan 05, 2017 at 09:17:00AM -0600, Josh Poimboeuf wrote:
> >> On Thu, Jan 05, 2017 at 03:59:52PM +0100, Dmitry Vyukov wrote:
> >> > On Thu, Jan 5, 2017 at 3:49 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >> > > On Tue, Dec 27, 2016 at 05:38:59PM +0100, Dmitry Vyukov wrote:
> >> > >> On Thu, Dec 22, 2016 at 6:17 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >> > >> > On Wed, Dec 21, 2016 at 01:46:36PM +0100, Andrey Konovalov wrote:
> >> > >> >> On Wed, Dec 21, 2016 at 12:36 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >> > >> >> >
> >> > >> >> > Thanks. Looking at the stack trace, my guess is that an interrupt hit
> >> > >> >> > while running in generated BPF code, and the unwinder got confused
> >> > >> >> > because regs->ip points to the generated code. I may need to disable
> >> > >> >> > that warning until we figure out a better solution.
> >> > >> >> >
> >> > >> >> > Can you share your .config file?
> >> > >> >>
> >> > >> >> Sure, attached.
> >> > >> >
> >> > >> > Ok, I was able to recreate with your config. The culprit was generated
> >> > >> > code, as I suspected, though it wasn't BPF, it was a kprobe (created by
> >> > >> > dccpprobe_init()).
> >> > >> >
> >> > >> > I'll make a patch to disable the warning.
> >> > >>
> >> > >> Hi,
> >> > >>
> >> > >> I am also seeing the following warnings:
> >> > >>
> >> > >> [ 281.889259] WARNING: kernel stack regs at ffff8801c29a7ea8 in
> >> > >> syz-executor8:1302 has bad 'bp' value ffff8801c29a7f28
> >> > >> [ 833.994878] WARNING: kernel stack regs at ffff8801c4e77ea8 in
> >> > >> syz-executor1:13094 has bad 'bp' value ffff8801c4e77f28
> >> > >>
> >> > >> Can it also be caused by bpf/kprobe?
> >> > >
> >> > > This is a different warning. I suspect it's due to unwinding the stack
> >> > > of another CPU while it's running, which is still possible in a few
> >> > > places. I'm going to have to disable all these warnings for now.
> >> >
> >> >
> >> > I also have the following diff locally. These loads trigger episodic
> >> > KASAN warnings about stack-of-bounds reads on rcu stall warnings when
> >> > it does backtrace of all cpus.
> >> > If it looks correct to you, can you please also incorporate it into your patch?
> >>
> >> Ok, will do.
> >>
> >> BTW, I think there's an issue with your mail client. Your last two
> >> replies to me didn't have me on To/Cc.
> >
> > Would you mind testing if the following patch fixes it? It's based on
> > the latest linus/master.
> >
> >
> > diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
> > index 4443e49..05adf9a 100644
> > --- a/arch/x86/kernel/unwind_frame.c
> > +++ b/arch/x86/kernel/unwind_frame.c
> > @@ -6,6 +6,21 @@
> >
> > #define FRAME_HEADER_SIZE (sizeof(long) * 2)
> >
> > +/*
> > + * This disables KASAN checking when reading a value from another task's stack,
> > + * since the other task could be running on another CPU and could have poisoned
> > + * the stack in the meantime.
> > + */
> > +#define UNWIND_READ_ONCE(state, x) \
> > +({ \
> > + unsigned long val; \
> > + if (state->task == current) \
> > + val = READ_ONCE(x); \
> > + else \
> > + val = READ_ONCE_NOCHECK(x); \
> > + val; \
> > +})
> > +
> > static void unwind_dump(struct unwind_state *state, unsigned long *sp)
> > {
> > static bool dumped_before = false;
> > @@ -48,7 +63,8 @@ unsigned long unwind_get_return_address(struct unwind_state *state)
> > if (state->regs && user_mode(state->regs))
> > return 0;
> >
> > - addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, *addr_p,
> > + addr = UNWIND_READ_ONCE(state, *addr_p);
> > + addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, addr,
> > addr_p);
> >
> > return __kernel_text_address(addr) ? addr : 0;
> > @@ -162,7 +178,7 @@ bool unwind_next_frame(struct unwind_state *state)
> > if (state->regs)
> > next_bp = (unsigned long *)state->regs->bp;
> > else
> > - next_bp = (unsigned long *)*state->bp;
> > + next_bp = (unsigned long *)UNWIND_READ_ONCE(state, *state->bp);
> >
> > /* is the next frame pointer an encoded pointer to pt_regs? */
> > regs = decode_frame_pointer(next_bp);
> > @@ -207,6 +223,16 @@ bool unwind_next_frame(struct unwind_state *state)
> > return true;
> >
> > bad_address:
> > + /*
> > + * When dumping a task other than current, the task might actually be
> > + * running on another CPU, in which case it could be modifying its
> > + * stack while we're reading it. This is generally not a problem and
> > + * can be ignored as long as the caller understands that unwinding
> > + * another task will not always succeed.
> > + */
> > + if (state->task != current)
> > + goto the_end;
> > +
> > if (state->regs) {
> > printk_deferred_once(KERN_WARNING
> > "WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",
>
>
> Applied locally for testing.
>
>
> What about this part?
>
> diff --git a/arch/x86/include/asm/stacktrace.h
> b/arch/x86/include/asm/stacktrace.h
> index a3269c897ec5..d8d4fc66ffec 100644
> --- a/arch/x86/include/asm/stacktrace.h
> +++ b/arch/x86/include/asm/stacktrace.h
> @@ -58,7 +58,7 @@ get_frame_pointer(struct task_struct *task, struct
> pt_regs *regs)
> if (task == current)
> return __builtin_frame_address(0);
>
> - return (unsigned long *)((struct
> inactive_task_frame*)task->thread.sp)->bp;
> + return (unsigned long *)READ_ONCE_NOCHECK(((struct
> inactive_task_frame *)task->thread.sp)->bp);
> }
> #else
> static inline unsigned long *
Oops, I missed that part. That's needed too.
BTW, I'm still not on your email To: list.
--
Josh
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