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Subject[BUGFIX PATCH tip/master 3/3] kprobes/arm: Fix a possible deadlock case in kretprobe
Date
Similar to x86 kretprobe deadlock issue, arm also implements
kretprobe-booster (trampoline code directly call handler.)
So it has same deadlock issue if there are 2 kretprobes on
normal function and the function called from FIQ (or anywhere
which can be invoked when local_irq_disabled).

This fixes the issue as same as we did on x86.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
arch/arm/probes/kprobes/core.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
index b6dc9d8..3e5aab7 100644
--- a/arch/arm/probes/kprobes/core.c
+++ b/arch/arm/probes/kprobes/core.c
@@ -426,6 +426,8 @@ void __naked __kprobes kretprobe_trampoline(void)
: : : "memory");
}

+static struct kprobe dummy_retprobe = {.addr = (void *)&kretprobe_trampoline};
+
/* Called from kretprobe_trampoline */
static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
{
@@ -436,6 +438,11 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;

INIT_HLIST_HEAD(&empty_rp);
+
+ /* This prevents kernel to change running cpu while processing */
+ preempt_disable();
+ get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
+ __this_cpu_write(current_kprobe, &dummy_retprobe);
kretprobe_hash_lock(current, &head, &flags);

/*
@@ -458,9 +465,8 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs)

if (ri->rp && ri->rp->handler) {
__this_cpu_write(current_kprobe, &ri->rp->kp);
- get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
ri->rp->handler(ri, regs);
- __this_cpu_write(current_kprobe, NULL);
+ __this_cpu_write(current_kprobe, &dummy_retprobe);
}

orig_ret_address = (unsigned long)ri->ret_addr;
@@ -477,6 +483,8 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs)

kretprobe_assert(ri, orig_ret_address, trampoline_address);
kretprobe_hash_unlock(current, &flags);
+ __this_cpu_write(current_kprobe, NULL);
+ preempt_enable_no_resched();

hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
hlist_del(&ri->hlist);
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