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arm64: kprobes: Allow reentering kprobes while single-stepping

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A kprobe can be hit while another kprobe is in KPROBE_HIT_SS state. This
can happen when tracing or perf code runs from the debug exception path
while the first kprobe is preparing or executing its out-of-line
single-step instruction.

Currently arm64 treats a kprobe hit in KPROBE_HIT_SS as unrecoverable,
the same as a hit in KPROBE_REENTER. This is too strict. A hit in
KPROBE_HIT_SS is still a one-level reentry and can be handled by saving
the current kprobe state and setting up single-step for the new probe,
just like reentry from KPROBE_HIT_ACTIVE or KPROBE_HIT_SSDONE.

The truly unrecoverable case is hitting another kprobe while already in
KPROBE_REENTER, because the reentry save area has already been consumed.

Move KPROBE_HIT_SS to the recoverable reentry cases and leave
KPROBE_REENTER as the unrecoverable nested reentry case.

This change also requires saving saved_irqflag in struct prev_kprobe.
When a nested kprobe calls kprobes_save_local_irqflag(), it overwrites
kcb->saved_irqflag with the currently masked DAIF value, losing the
outer kprobe's original DAIF state. Without this fix, when the outer
kprobe's single-step finishes, kprobes_restore_local_irqflag() applies
the wrong DAIF mask and leaves interrupts permanently disabled.

Extend struct prev_kprobe with a saved_irqflag field and save/restore it
alongside kp and status. This ensures the outer kprobe's original
interrupt state is preserved across reentry.

This mirrors the x86 fix in commit 6a5022a56a
("kprobes/x86: Allow to handle reentered kprobe on single-stepping").

Signed-off-by: Pu Hu <hupu@transsion.com>
Signed-off-by: Hongyan Xia <hongyan.xia@transsion.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Pu Hu 2026-07-10 06:32:55 +00:00 committed by Will Deacon
parent 879a6754d3
commit 23f851ac00
2 changed files with 28 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
arch/arm64/include/asm/kprobes.h
View File

@ -26,6 +26,12 @@
struct prev_kprobe {
struct kprobe *kp;
unsigned int status;
/*
* The original DAIF state of the outer kprobe, saved here before
* a nested kprobe overwrites kcb->saved_irqflag during reentry.
*/
unsigned long saved_irqflag;
};
/* per-cpu kprobe control block */

23
arch/arm64/kernel/probes/kprobes.c
View File

@ -174,12 +174,27 @@ static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
kcb->prev_kprobe.kp = kprobe_running();
kcb->prev_kprobe.status = kcb->kprobe_status;
/*
* Save the outer kprobe's original DAIF flags before the nested
* kprobe calls kprobes_save_local_irqflag() and overwrites
* kcb->saved_irqflag. Without this, the outer kprobe will restore
* the wrong DAIF state and leave interrupts permanently masked.
*/
kcb->prev_kprobe.saved_irqflag = kcb->saved_irqflag;
}
static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
{
__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
kcb->kprobe_status = kcb->prev_kprobe.status;
/*
* Restore the outer kprobe's saved_irqflag so that when its
* single-step completes, kprobes_restore_local_irqflag() uses
* the correct original DAIF value.
*/
kcb->saved_irqflag = kcb->prev_kprobe.saved_irqflag;
}
static void __kprobes set_current_kprobe(struct kprobe *p)
@ -240,10 +255,16 @@ static int __kprobes reenter_kprobe(struct kprobe *p,
switch (kcb->kprobe_status) {
case KPROBE_HIT_SSDONE:
case KPROBE_HIT_ACTIVE:
case KPROBE_HIT_SS:
/*
* A probe can be hit while another kprobe is preparing or
* executing its XOL single-step instruction. This is still a
* recoverable one-level reentry, so handle it in the same way as
* reentry from KPROBE_HIT_ACTIVE or KPROBE_HIT_SSDONE.
*/
kprobes_inc_nmissed_count(p);
setup_singlestep(p, regs, kcb, 1);
break;
case KPROBE_HIT_SS:
case KPROBE_REENTER:
pr_warn("Failed to recover from reentered kprobes.\n");
dump_kprobe(p);