* [PATCH] Wrong symbol resolved for RIP on OOPS/BUG
@ 2013-11-06 19:59 Marek Majkowski
2013-11-07 7:54 ` Ingo Molnar
0 siblings, 1 reply; 4+ messages in thread
From: Marek Majkowski @ 2013-11-06 19:59 UTC (permalink / raw)
To: Thomas Gleixner, Ingo Molnar, H. Peter Anvin, x86
Cc: Rusty Russell, linux-kernel, Marek Majkowski
"%pB" is intended for return addresses, and actually resolves the
address - 1. So it should only be used for backtraces. Plain
instruction addresses should use "%pS", which resolves the given
address.
show_regs was using "%pB" to resolve the RIP symbol. This resolved the
wrong symbol if the first instruction after a symbol created the
OOPS/BUG. For example:
0000000000000049 <before>:
49: 90 nop
4a: 90 nop
4b: 90 nop
4c: 90 nop
000000000000004d <suicide>:
4d: ff 14 25 00 00 00 00 callq *0x0
54: c3 retq
Will produce a message saying it's "before" that crashed, not "suicide".
This problem only happens when the crash occurs in the first instruction
after a symbol. Therefore it's unlikely to occur on kernels with frame
pointers (CONFIG_FRAME_POINTER=y).
Signed-off-by: Marek Majkowski <marek@cloudflare.com>
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index deb6421..4c90013 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -27,6 +27,12 @@ static int die_counter;
void printk_address(unsigned long address, int reliable)
{
+ pr_cont(" [<%p>] %s%pS\n",
+ (void *)address, reliable ? "" : "? ", (void *)address);
+}
+
+static void printk_trace_address(unsigned long address, int reliable)
+{
pr_cont(" [<%p>] %s%pB\n",
(void *)address, reliable ? "" : "? ", (void *)address);
}
@@ -151,7 +157,7 @@ static void print_trace_address(void *data, unsigned long addr, int reliable)
{
touch_nmi_watchdog();
printk(data);
- printk_address(addr, reliable);
+ printk_trace_address(addr, reliable);
}
static const struct stacktrace_ops print_trace_ops = {
--
1.8.3.2
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] Wrong symbol resolved for RIP on OOPS/BUG
2013-11-06 19:59 [PATCH] Wrong symbol resolved for RIP on OOPS/BUG Marek Majkowski
@ 2013-11-07 7:54 ` Ingo Molnar
2013-11-07 16:25 ` H. Peter Anvin
0 siblings, 1 reply; 4+ messages in thread
From: Ingo Molnar @ 2013-11-07 7:54 UTC (permalink / raw)
To: Marek Majkowski, Jiri Slaby
Cc: Thomas Gleixner, Ingo Molnar, H. Peter Anvin, x86, Rusty Russell,
linux-kernel
* Marek Majkowski <marek@cloudflare.com> wrote:
> "%pB" is intended for return addresses, and actually resolves the
> address - 1. So it should only be used for backtraces. Plain
> instruction addresses should use "%pS", which resolves the given
> address.
>
> show_regs was using "%pB" to resolve the RIP symbol. This resolved the
> wrong symbol if the first instruction after a symbol created the
> OOPS/BUG. For example:
>
> 0000000000000049 <before>:
> 49: 90 nop
> 4a: 90 nop
> 4b: 90 nop
> 4c: 90 nop
> 000000000000004d <suicide>:
> 4d: ff 14 25 00 00 00 00 callq *0x0
> 54: c3 retq
>
> Will produce a message saying it's "before" that crashed, not "suicide".
>
> This problem only happens when the crash occurs in the first instruction
> after a symbol. Therefore it's unlikely to occur on kernels with frame
> pointers (CONFIG_FRAME_POINTER=y).
>
> Signed-off-by: Marek Majkowski <marek@cloudflare.com>
>
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index deb6421..4c90013 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -27,6 +27,12 @@ static int die_counter;
>
> void printk_address(unsigned long address, int reliable)
> {
> + pr_cont(" [<%p>] %s%pS\n",
> + (void *)address, reliable ? "" : "? ", (void *)address);
> +}
> +
> +static void printk_trace_address(unsigned long address, int reliable)
> +{
> pr_cont(" [<%p>] %s%pB\n",
> (void *)address, reliable ? "" : "? ", (void *)address);
> }
> @@ -151,7 +157,7 @@ static void print_trace_address(void *data, unsigned long addr, int reliable)
> {
> touch_nmi_watchdog();
> printk(data);
> - printk_address(addr, reliable);
> + printk_trace_address(addr, reliable);
> }
>
> static const struct stacktrace_ops print_trace_ops = {
There's a recent commit from Jiri Slaby that I think tries to address the
same problem:
8d4c812a3e5f x86/dumpstack: Fix printk_address for direct addresses
You can find it in the -tip tree:
git remote add tip git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
Thanks,
Ingo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Wrong symbol resolved for RIP on OOPS/BUG
2013-11-07 7:54 ` Ingo Molnar
@ 2013-11-07 16:25 ` H. Peter Anvin
2013-11-11 11:45 ` Ingo Molnar
0 siblings, 1 reply; 4+ messages in thread
From: H. Peter Anvin @ 2013-11-07 16:25 UTC (permalink / raw)
To: Ingo Molnar, Marek Majkowski, Jiri Slaby
Cc: Thomas Gleixner, Ingo Molnar, x86, Rusty Russell, linux-kernel
On 11/06/2013 11:54 PM, Ingo Molnar wrote:
>
> There's a recent commit from Jiri Slaby that I think tries to address the
> same problem:
>
> 8d4c812a3e5f x86/dumpstack: Fix printk_address for direct addresses
>
> You can find it in the -tip tree:
>
> git remote add tip git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
>
The only difference seems to be in the handling of the "reliable" flag.
I am wondering if we shouldn't promote this patch to urgent/stable,
though, since misleading oops messages could be very disruptive.
-hpa
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Wrong symbol resolved for RIP on OOPS/BUG
2013-11-07 16:25 ` H. Peter Anvin
@ 2013-11-11 11:45 ` Ingo Molnar
0 siblings, 0 replies; 4+ messages in thread
From: Ingo Molnar @ 2013-11-11 11:45 UTC (permalink / raw)
To: H. Peter Anvin
Cc: Marek Majkowski, Jiri Slaby, Thomas Gleixner, Ingo Molnar, x86,
Rusty Russell, linux-kernel
* H. Peter Anvin <hpa@zytor.com> wrote:
> On 11/06/2013 11:54 PM, Ingo Molnar wrote:
> >
> > There's a recent commit from Jiri Slaby that I think tries to address the
> > same problem:
> >
> > 8d4c812a3e5f x86/dumpstack: Fix printk_address for direct addresses
> >
> > You can find it in the -tip tree:
> >
> > git remote add tip git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
> >
>
> The only difference seems to be in the handling of the "reliable" flag.
>
> I am wondering if we shouldn't promote this patch to urgent/stable,
> though, since misleading oops messages could be very disruptive.
Sure, no objections.
Thanks,
Ingo
^ permalink raw reply [flat|nested] 4+ messages in thread
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2013-11-06 19:59 [PATCH] Wrong symbol resolved for RIP on OOPS/BUG Marek Majkowski
2013-11-07 7:54 ` Ingo Molnar
2013-11-07 16:25 ` H. Peter Anvin
2013-11-11 11:45 ` Ingo Molnar
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