Re: [PATCH 2/4] arm64: Extract kprobes_save_local_irqflag() and kprobes_restore_local_irqflag()

On Sat, 16 May 2020 09:17:21 -0700
Doug Anderson [off-list ref] wrote:

Hi,

On Sat, May 16, 2020 at 1:47 AM liwei (GF) [off-list ref] wrote:

quoted

quoted

quoted

-               kprobes_save_local_irqflag(kcb, regs);
+               kernel_prepare_single_step(&kcb->saved_irqflag, regs);

Is there some reason to have two functions?  It seems like every time
you call kernel_enable_single_step() you'd want to call
kernel_prepare_single_step().  ...and every time you call
kernel_disable_single_step() you'd want to call
kernel_cleanup_single_step().

Maybe you can just add the flags parameter to
kernel_enable_single_step() / kernel_disable_single_step() and put the
code in there?

As kernel_enable_single_step() / kernel_disable_single_step() are also called in
breakpoint_handler() and watchpoint_handler(), i am not sure it's a right thing
to put the daif flag prepare/cleanup into them, especially we don't have a context
to save the flags.

I think you misunderstood what I was suggesting.  Maybe better with
examples?  I was suggesting doing this:

kcb->saved_irqflag = kernel_enable_single_step(regs);
...
kernel_disable_single_step(kcb->saved_irqflag, regs);

To me that seems better than what you have now:

kcb->saved_irqflag = kernel_prepare_single_step(regs);
kernel_enable_single_step(regs);
...
kernel_cleanup_single_step(kcb->saved_irqflag, regs);
kernel_disable_single_step();

...or am I confused?

+1, this sounds good to me. Currently arch/arm64/kernel/probes/kprobes.c
has a code which sololy use kernel_disable_single_step() without regs
restoring, but it looks like a bug there. So maybe you need following patch.

Thank you,

-----
From: Masami Hiramatsu <mhiramat@kernel.org>
Date: Mon, 18 May 2020 23:08:28 +0900
Subject: [PATCH] arm64: kprobes: Restore saved interrupt flag before disabling
 single step

Restore the saved interrupt flag in kprobe_ctlblk to regs->pstate
when a page fault happens on single-stepping instruction.
Without this fix, we will lose the flag if it happens because
kcb->saved_irqflag only knows the previous flag.

Fixes: 2dd0e8d2d2a1 ("arm64: Kprobes with single stepping support")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
---
 arch/arm64/kernel/probes/kprobes.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index d1c95dcf1d78..73fb99770f69 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c

@@ -308,6 +308,7 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 		if (!instruction_pointer(regs))
 			BUG();
 
+		kprobes_restore_local_irqflag(kcb, regs);
 		kernel_disable_single_step();
 
 		if (kcb->kprobe_status == KPROBE_REENTER)

-- 
2.25.1




-- 
Masami Hiramatsu <mhiramat@kernel.org>

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