Re: [PATCH v3 0/5] ARM64: Add kernel probes(Kprobes) support
From: David Long
Date: Mon Dec 15 2014 - 01:29:33 EST
On 12/12/14 18:10, Steve Capper wrote:
On 12 December 2014 at 22:42, David Long <dave.long@xxxxxxxxxx> wrote:
On 12/10/14 11:38, Steve Capper wrote:
On Tue, Dec 09, 2014 at 09:27:18AM -0500, David Long wrote:
On 12/09/14 08:33, Steve Capper wrote:
On Thu, Dec 04, 2014 at 08:53:03PM +0900, Masami Hiramatsu wrote:
[...]
Not sure if this is helpful, but the following also caused a crash for
me:
echo "p:trace_event_buffer_lock_reserve trace_event_buffer_lock_reserve"
/sys/kernel/debug/tracing/kprobe_events
echo "p:memcpy memcpy" >> /sys/kernel/debug/tracing/kprobe_events
echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
[immediate crash]
The crash point for me is in the arm64 ASID allocator, it again looks
like the interrupts are in an unexpected state.
(check_and_switch_context goes down the irqs disabled code path, I
think incorrectly).
This occurred for me both with and without the proposed irq saving fix.
I will do some more digging.
Thanks, more information is good.
Hi,
Some good news, I think I've fixed the problem I've been experiencing.
Basically, I've torn out all the interrupt save/restore and have
narrowed the scope to just sandwich the instruction single-step. This
simplifies a lot of logic, and I've now been able to perf record a
kprobe on memcpy (and the trace_event_buffer_lock_reserve + memcpy
test) without any issues on a Juno platform.
I may have been somewhat over-zealous with the chainsaw, so please do
put this fix through its paces.
Cheers,
--
Steve
From d3f4d80ce19bec71bd03209beb2fbfd8084d6543 Mon Sep 17 00:00:00 2001
From: Steve Capper <steve.capper@xxxxxxxxxx>
Date: Mon, 1 Dec 2014 11:30:10 +0000
Subject: [PATCH] Fix the interrupt handling for kprobes
---
arch/arm64/kernel/kprobes.c | 16 ++--------------
1 file changed, 2 insertions(+), 14 deletions(-)
diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
index be7c330..d39d826 100644
--- a/arch/arm64/kernel/kprobes.c
+++ b/arch/arm64/kernel/kprobes.c
@@ -229,10 +229,6 @@ skip_singlestep_missed(struct kprobe_ctlblk *kcb,
struct pt_regs *regs)
{
/* set return addr to next pc to continue */
instruction_pointer(regs) += sizeof(kprobe_opcode_t);
-
- if (kcb->kprobe_status != KPROBE_REENTER)
- kprobes_restore_local_irqflag(regs);
-
}
static void __kprobes setup_singlestep(struct kprobe *p,
@@ -259,7 +255,7 @@ static void __kprobes setup_singlestep(struct kprobe
*p,
spsr_set_debug_flag(regs, 0);
/* IRQs and single stepping do not mix well. */
- local_irq_disable();
+ kprobes_save_local_irqflag(regs);
kernel_enable_single_step(regs);
instruction_pointer(regs) = slot;
} else {
@@ -326,7 +322,6 @@ post_kprobe_handler(struct kprobe_ctlblk *kcb, struct
pt_regs *regs)
}
reset_current_kprobe();
- kprobes_restore_local_irqflag(regs);
}
int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int
fsr)
@@ -380,8 +375,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs
*regs, unsigned int fsr)
return 1;
break;
- default:
- break;
}
return 0;
}
@@ -446,7 +439,6 @@ void __kprobes kprobe_handler(struct pt_regs *regs)
* handling of this interrupt is appropriate.
* Return back to original instruction, and continue.
*/
- kprobes_restore_local_irqflag(regs);
return;
} else if (cur) {
/* We probably hit a jprobe. Call its break handler. */
@@ -459,7 +451,6 @@ void __kprobes kprobe_handler(struct pt_regs *regs)
/* breakpoint is removed, now in a race
* Return back to original instruction & continue.
*/
- kprobes_restore_local_irqflag(regs);
}
}
@@ -485,6 +476,7 @@ kprobe_single_step_handler(struct pt_regs *regs,
unsigned int esr)
retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
if (retval == DBG_HOOK_HANDLED) {
+ kprobes_restore_local_irqflag(regs);
kernel_disable_single_step();
if (kcb->kprobe_status == KPROBE_REENTER)
@@ -499,7 +491,6 @@ kprobe_single_step_handler(struct pt_regs *regs,
unsigned int esr)
static int __kprobes
kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
{
- kprobes_save_local_irqflag(regs);
kprobe_handler(regs);
return DBG_HOOK_HANDLED;
}
@@ -563,7 +554,6 @@ int __kprobes longjmp_break_handler(struct kprobe *p,
struct pt_regs *regs)
memcpy((void *)stack_addr, kcb->jprobes_stack,
MIN_STACK_SIZE(stack_addr));
preempt_enable_no_resched();
- kprobes_restore_local_irqflag(regs);
return 1;
}
return 0;
@@ -655,8 +645,6 @@ trampoline_probe_handler(struct kprobe *p, struct
pt_regs *regs)
kfree(ri);
}
- kprobes_restore_local_irqflag(regs);
-
/* return 1 so that post handlers not called */
return 1;
}
Sorry for the delay in responding. The assumption with the existing code is
that you can't enable single-stepping in MDSCR until you disable interrupts.
But since we get to that point (in this case) with debug exceptions masked
in daif I suppose this is an unnecessary constraint, as you have
demonstrated. I do actually wonder if we need to set the bit in MDSCR_EL1
at all since we're also setting it in the spsr in the regs structure that
will be restored when the eret is done, but it looks like
kernel_enable_single_step() sets both.
I do think we need to disable interrupts, but only when we're about to
single-step.
(My explanation before was imprecise, apologies).
The change I posted disables interrupts in __kprobes_single_step, and
restores them in kprobe_single_step_handler.
I did try removing the interrupt logic completely, but this then
resulted in a system hang after a few seconds.
I worded that badly. You still have to disable interrupts but I had
thought we needed to do that before setting SS in MDSCR. You've shown
we can do it anytime before we unmask debug exceptions.
I will think about MDSCR_EL1, when I'm awake :-).
Cheers,
--
Steve
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