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Groups > linux.kernel > #1552023 > unrolled thread
| Started by | Josh Poimboeuf <jpoimboe@redhat.com> |
|---|---|
| First post | 2017-01-05 15:50 +0100 |
| Last post | 2017-01-05 21:40 +0100 |
| Articles | 6 — 2 participants |
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Re: x86: warning in unwind_get_return_address Josh Poimboeuf <jpoimboe@redhat.com> - 2017-01-05 15:50 +0100
Re: x86: warning in unwind_get_return_address Dmitry Vyukov <dvyukov@google.com> - 2017-01-05 16:20 +0100
Re: x86: warning in unwind_get_return_address Josh Poimboeuf <jpoimboe@redhat.com> - 2017-01-05 16:20 +0100
Re: x86: warning in unwind_get_return_address Josh Poimboeuf <jpoimboe@redhat.com> - 2017-01-05 18:10 +0100
Re: x86: warning in unwind_get_return_address Dmitry Vyukov <dvyukov@google.com> - 2017-01-05 21:30 +0100
Re: x86: warning in unwind_get_return_address Josh Poimboeuf <jpoimboe@redhat.com> - 2017-01-05 21:40 +0100
| From | Josh Poimboeuf <jpoimboe@redhat.com> |
|---|---|
| Date | 2017-01-05 15:50 +0100 |
| Subject | Re: x86: warning in unwind_get_return_address |
| Message-ID | <sWhwB-4ll-5@gated-at.bofh.it> |
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@redhat.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@redhat.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. -- Josh
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| From | Dmitry Vyukov <dvyukov@google.com> |
|---|---|
| Date | 2017-01-05 16:20 +0100 |
| Message-ID | <sWhZE-4MO-15@gated-at.bofh.it> |
| In reply to | #1552023 |
On Thu, Jan 5, 2017 at 3:49 PM, Josh Poimboeuf <jpoimboe@redhat.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@redhat.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@redhat.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?
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 *
diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index 4443e499f279..f3a225ffa231 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -162,7 +162,7 @@ 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 *)READ_ONCE_NOCHECK(*state->bp);
/* is the next frame pointer an encoded pointer to pt_regs? */
regs = decode_frame_pointer(next_bp);
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| From | Josh Poimboeuf <jpoimboe@redhat.com> |
|---|---|
| Date | 2017-01-05 16:20 +0100 |
| Message-ID | <sWhZE-4MO-43@gated-at.bofh.it> |
| In reply to | #1552049 |
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@redhat.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@redhat.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@redhat.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. -- Josh
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| From | Josh Poimboeuf <jpoimboe@redhat.com> |
|---|---|
| Date | 2017-01-05 18:10 +0100 |
| Message-ID | <sWjI5-5Ut-5@gated-at.bofh.it> |
| In reply to | #1552052 |
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@redhat.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@redhat.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@redhat.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",
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| From | Dmitry Vyukov <dvyukov@google.com> |
|---|---|
| Date | 2017-01-05 21:30 +0100 |
| Message-ID | <sWmPD-7Tp-29@gated-at.bofh.it> |
| In reply to | #1552114 |
On Thu, Jan 5, 2017 at 6:03 PM, Josh Poimboeuf <jpoimboe@redhat.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@redhat.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@redhat.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@redhat.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 *
I am hitting it as welL:
[< inline >] kasan_report_error mm/kasan/report.c:213
[< none >] kasan_report+0x42d/0x460 mm/kasan/report.c:307
[< none >] __asan_report_load8_noabort+0x14/0x20
mm/kasan/report.c:333
[< inline >] get_frame_pointer ./arch/x86/include/asm/stacktrace.h:61
[< none >] __unwind_start+0x38d/0x3a0
arch/x86/kernel/unwind_frame.c:247
[< inline >] unwind_start ./arch/x86/include/asm/unwind.h:40
[< none >] show_trace_log_lvl+0x1ed/0x2c0
arch/x86/kernel/dumpstack.c:61
[< none >] show_stack+0x2f/0x40 arch/x86/kernel/dumpstack.c:174
[< none >] sched_show_task+0x3e4/0x540 kernel/sched/core.c:5217
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| From | Josh Poimboeuf <jpoimboe@redhat.com> |
|---|---|
| Date | 2017-01-05 21:40 +0100 |
| Message-ID | <sWmZk-7WS-31@gated-at.bofh.it> |
| In reply to | #1552308 |
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@redhat.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@redhat.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@redhat.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@redhat.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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