arm64: kprobes: Restore local irqflag if kprobes is cancelled

If instruction being single stepped caused a page fault, the kprobes is cancelled to let the page fault handler continue as a normal page fault. But the local irqflags are disabled so cpu will restore pstate with DAIF masked. After pagefault is serviced, the kprobes is triggerred again, we overwrite the saved_irqflag by calling kprobes_save_local_irqflag(). NOTE, DAIF is masked in this new saved irqflag. After kprobes is serviced, the cpu pstate is retored with DAIF masked.

This patch is inspired by one patch for riscv from Liao Chang.

Signed-off-by Jisheng Zhang <[email protected]>

---
 arch/arm64/kernel/probes/kprobes.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

arch/arm64/kernel/probes/kprobes.c +4 -2

index 66aac2881ba8..85645b2b0c7a 100644
@@ -267,10 +267,12 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 		if (!instruction_pointer(regs))
 			BUG();
 
-		if (kcb->kprobe_status == KPROBE_REENTER)
+		if (kcb->kprobe_status == KPROBE_REENTER) {
 			restore_previous_kprobe(kcb);
-		else
+		} else {
+			kprobes_restore_local_irqflag(kcb, regs);
 			reset_current_kprobe();
+		}
 
 		break;
 	case KPROBE_HIT_ACTIVE:

Signature · 1 line

2.31.0

Hi Jisheng,

Quoted 9 lines · On Mon, 12 Apr 2021 17:41:01 +0800 Jisheng Zhang <[email protected]>…

If instruction being single stepped caused a page fault, the kprobes is cancelled to let the page fault handler continue as a normal page fault. But the local irqflags are disabled so cpu will restore pstate with DAIF masked. After pagefault is serviced, the kprobes is triggerred again, we overwrite the saved_irqflag by calling kprobes_save_local_irqflag(). NOTE, DAIF is masked in this new saved irqflag. After kprobes is serviced, the cpu pstate is retored with DAIF masked.

Quoted 1 line

This patch is inspired by one patch for riscv from Liao Chang.

Thanks for pointing it out. But I think kprobes_restore_local_irqflag() is also needed for kcb->kprobe_status == KPROBE_REENTER case...no. This is more complicated. In the reenter case, I think we have to retry the kpreprobe_fault_handler() with recovered previous kprobes so that it can handle page fault in its handler.

Hmm, RISC-V and other code also needs same fix.

Thank you,

Quoted 28 lines

Signed-off-by Jisheng Zhang <[email protected]>

---
 arch/arm64/kernel/probes/kprobes.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

arch/arm64/kernel/probes/kprobes.c +4 -2

index 66aac2881ba8..85645b2b0c7a 100644
@@ -267,10 +267,12 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 		if (!instruction_pointer(regs))
 			BUG();
 
-		if (kcb->kprobe_status == KPROBE_REENTER)
+		if (kcb->kprobe_status == KPROBE_REENTER) {
 			restore_previous_kprobe(kcb);
-		else
+		} else {
+			kprobes_restore_local_irqflag(kcb, regs);
 			reset_current_kprobe();
+		}
 
 		break;
 	case KPROBE_HIT_ACTIVE:

Signature · 1 line

2.31.0

Signature · 1 line

Masami Hiramatsu <[email protected]>

If instruction being single stepped caused a page fault, the kprobes is cancelled to let the page fault handler continue as a normal page fault. But the local irqflags are disabled so cpu will restore pstate with DAIF masked. After pagefault is serviced, the kprobes is triggerred again, we overwrite the saved_irqflag by calling kprobes_save_local_irqflag(). NOTE, DAIF is masked in this new saved irqflag. After kprobes is serviced, the cpu pstate is retored with DAIF masked.

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