[PATCH 4/5] powerpc/jprobes: Disable preemption when triggered through ftrace

[Masami Hiramatsu]

On Thu, 14 Sep 2017 02:50:35 +0530
"Naveen N. Rao" <naveen.n.rao at linux.vnet.ibm.com> wrote:

> KPROBES_SANITY_TEST throws the below splat when CONFIG_PREEMPT is
> enabled:
> 
> [    3.140410] Kprobe smoke test: started
> [    3.149680] DEBUG_LOCKS_WARN_ON(val > preempt_count())
> [    3.149684] ------------[ cut here ]------------
> [    3.149695] WARNING: CPU: 19 PID: 1 at kernel/sched/core.c:3094 preempt_count_sub+0xcc/0x140
> [    3.149699] Modules linked in:
> [    3.149705] CPU: 19 PID: 1 Comm: swapper/0 Not tainted 4.13.0-rc7-nnr+ #97
> [    3.149709] task: c0000000fea80000 task.stack: c0000000feb00000
> [    3.149713] NIP:  c00000000011d3dc LR: c00000000011d3d8 CTR: c000000000a090d0
> [    3.149718] REGS: c0000000feb03400 TRAP: 0700   Not tainted  (4.13.0-rc7-nnr+)
> [    3.149722] MSR:  8000000000021033 <SF,ME,IR,DR,RI,LE>  CR: 28000282  XER: 00000000
> [    3.149732] CFAR: c00000000015aa18 SOFTE: 0
> <snip>
> [    3.149786] NIP [c00000000011d3dc] preempt_count_sub+0xcc/0x140
> [    3.149790] LR [c00000000011d3d8] preempt_count_sub+0xc8/0x140
> [    3.149794] Call Trace:
> [    3.149798] [c0000000feb03680] [c00000000011d3d8] preempt_count_sub+0xc8/0x140 (unreliable)
> [    3.149804] [c0000000feb036e0] [c000000000046198] kprobe_handler+0x228/0x4b0
> [    3.149810] [c0000000feb03750] [c0000000000269c8] program_check_exception+0x58/0x3b0
> [    3.149816] [c0000000feb037c0] [c00000000000903c] program_check_common+0x16c/0x170
> [    3.149822] --- interrupt: 0 at kprobe_target+0x8/0x20
>                    LR = init_test_probes+0x248/0x7d0
> [    3.149829] [c0000000feb03ab0] [c000000000e4f048] kp+0x0/0x80 (unreliable)
> [    3.149835] [c0000000feb03b10] [c00000000004ea60] livepatch_handler+0x38/0x74
> [    3.149841] [c0000000feb03ba0] [c000000000d0de54] init_kprobes+0x1d8/0x208
> [    3.149846] [c0000000feb03c40] [c00000000000daa8] do_one_initcall+0x68/0x1d0
> [    3.149852] [c0000000feb03d00] [c000000000ce44f0] kernel_init_freeable+0x298/0x374
> [    3.149857] [c0000000feb03dc0] [c00000000000dd84] kernel_init+0x24/0x160
> [    3.149863] [c0000000feb03e30] [c00000000000bfec] ret_from_kernel_thread+0x5c/0x70
> [    3.149867] Instruction dump:
> [    3.149871] 419effdc 3d22001b 39299240 81290000 2f890000 409effc8 3c82ffcb 3c62ffcb
> [    3.149879] 3884bc68 3863bc18 4803d5fd 60000000 <0fe00000> 4bffffa8 60000000 60000000
> [    3.149890] ---[ end trace 432dd46b4ce3d29f ]---
> [    3.166003] Kprobe smoke test: passed successfully
> 
> The issue is that we aren't disabling preemption in
> kprobe_ftrace_handler(). Disable it.

Oops, right! Similar patch may need for x86 too.

Acked-by: Masami Hiramatsu <mhiramat at kernel.org>

Thanks!

> Fixes: ead514d5fb30a0 ("powerpc/kprobes: Add support for KPROBES_ON_FTRACE")
> Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
> ---
>  arch/powerpc/kernel/kprobes-ftrace.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c
> index 6c089d9757c9..2d81404f818c 100644
> --- a/arch/powerpc/kernel/kprobes-ftrace.c
> +++ b/arch/powerpc/kernel/kprobes-ftrace.c
> @@ -65,6 +65,7 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip,
>  	/* Disable irq for emulating a breakpoint and avoiding preempt */
>  	local_irq_save(flags);
>  	hard_irq_disable();
> +	preempt_disable();
>  
>  	p = get_kprobe((kprobe_opcode_t *)nip);
>  	if (unlikely(!p) || kprobe_disabled(p))
> @@ -86,12 +87,18 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip,
>  		kcb->kprobe_status = KPROBE_HIT_ACTIVE;
>  		if (!p->pre_handler || !p->pre_handler(p, regs))
>  			__skip_singlestep(p, regs, kcb, orig_nip);
> -		/*
> -		 * If pre_handler returns !0, it sets regs->nip and
> -		 * resets current kprobe.
> -		 */
> +		else {
> +			/*
> +			 * If pre_handler returns !0, it sets regs->nip and
> +			 * resets current kprobe. In this case, we still need
> +			 * to restore irq, but not preemption.
> +			 */
> +			local_irq_restore(flags);
> +			return;
> +		}
>  	}
>  end:
> +	preempt_enable_no_resched();
>  	local_irq_restore(flags);
>  }
>  NOKPROBE_SYMBOL(kprobe_ftrace_handler);
> -- 
> 2.14.1
> 


-- 
Masami Hiramatsu <mhiramat at kernel.org>