Re: [PATCH] perf: fix kernel panic when parsing user space CS saved in pt_regs

[Peter Zijlstra]

On Thu, Jun 05, 2014 at 10:36:10AM +0800, Liu ShuoX wrote:
> From: Zhang Yanmin <yanmin.zhang@xxxxxxxxx>
> 
> We hit a kernel panic when running perf to collect some performance data.
> kenel is x86_64 and user space apps are 32bit.
> 
> [   71.965351, 1] [       Binder_2] BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
> [   71.965360, 1] [       Binder_2] IP: [<ffffffff82012091>] get_segment_base+0x71/0xc0
> [   71.965367, 1] [       Binder_2] PGD 6c65f067 PUD 0
> [   71.965375, 1] [       Binder_2] Oops: 0000 [#1] PREEMPT SMP
> [   71.965413, 1] [       Binder_2] Modules linked in: ddrgx snd_merr_dpcm_wm8958 snd_intel_sst snd_soc_sst_platform snd_soc_wm8994 snd_soc_wm_hubs lm3559 imx1x5 atomisp_css2401a0_v21 libmsrlisthelper rmi4 bcm_bt_lpm videobuf_vmalloc videobuf_core fps_throttle hdmi_audio pn544(O) tngdisp bcm4335(O) cfg80211
> [   71.965420, 1] [       Binder_2] CPU: 1 PID: 304 Comm: Binder_2 Tainted: G        W  O 3.10.20-263902-g184bfbc-dirty #14
> [   71.965426, 1] [       Binder_2] task: ffff8800764dc300 ti: ffff88006c6e8000 task.ti: ffff88006c6e8000
> [   71.965439, 1] [       Binder_2] RIP: 0010:[<ffffffff82012091>]  [<ffffffæf82012091>] get_segment_base+0x71/0xc0
                                                                              ^
> [   71.965<44, 1] [       Binder_2] RSP: 0018:ffff^X8007ea87b98  EFLAGS: 00010092
            ^                                       ^
> [   71.965447, 1] [      !Binder_2] RAX: 0000000000000024 RBX: 0000000000000000 RCX: 0000000000000000
                           ^
> [   71.965450, 1] [       Binder_2] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000009
> [   71.965454, 1] [       Binder_2] RBP: ffff88007ea87ba8 R08: ffffffff83143b3c R09: ffffffff831848a8
> [   71.965458, 1] [       Binder_2] R10: 0000000000000000 R11: 00000000001bf2d8 R12: 0000000000000000
> [   71.965462, 1] [       Binder_2] R13: ffff88006c6e9fd8 R14: ffff88006c6e9f58 R15: ffff8800764dc300
> [   71.965468, 1_ [       Binder_2] FS:  0000000000000000(0000) GS:ffff88007ea80000(006b) knlGS:00000000f704add0
                  ^

Are you suffering some serious corruption?

> Basically, ia32 uses sysenter to start system calls.
> 
> sysexit_from_sys_call=>trace_hardirqs_on_thunk. Before calling,
> sysexit_from_sys_call already pops up pt_regs, then trace_hardirqs_on_thunk
> would reuse pt_regs space. If perf NMI happens here, perf might use a bad pt_regs.
> 
> The patch fixes it  by moving the calling to trace_hardirqs_on_thunk ahead of
> the stack popup.
> 
> Change-Id: I6c4fc46b009ea056f2321ce5b8f54cf8769a7bdd

No idea what that is, but it needs to go.

I'll leave the actual patch to hpa, this isn't something I'm too
familiar with.

> Signed-off-by: Zhang Yanmin <yanmin.zhang@xxxxxxxxx>
> ---
>  arch/x86/ia32/ia32entry.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
> index 4299eb0..df61fdb 100644
> --- a/arch/x86/ia32/ia32entry.S
> +++ b/arch/x86/ia32/ia32entry.S
> @@ -167,6 +167,7 @@ sysenter_dispatch:
>  	testl	$_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)
>  	jnz	sysexit_audit
>  sysexit_from_sys_call:
> +	TRACE_IRQS_ON
>  	andl    $~TS_COMPAT,TI_status+THREAD_INFO(%rsp,RIP-ARGOFFSET)
>  	/* clear IF, that popfq doesn't enable interrupts early */
>  	andl  $~0x200,EFLAGS-R11(%rsp) @@ -181,7 +182,6 @@ sysexit_from_sys_call:
>  	/*CFI_RESTORE rflags*/
>  	popq_cfi %rcx				/* User %esp */
>  	CFI_REGISTER rsp,rcx
> -	TRACE_IRQS_ON
>  	ENABLE_INTERRUPTS_SYSEXIT32
>  #ifdef CONFIG_AUDITSYSCALL
> -- 
> 1.8.3.2
>

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