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Subject[PATCH 4.4 18/78] arm: kprobes: Fix the return address of multiple kretprobes
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Masami Hiramatsu <mhiramat@kernel.org>


[ Upstream commit 06553175f585b52509c7df37d6f4a50aacb7b211 ]

This is arm port of commit 737480a0d525 ("kprobes/x86:
Fix the return address of multiple kretprobes").

Fix the return address of subsequent kretprobes when multiple
kretprobes are set on the same function.

For example:

# cd /sys/kernel/debug/tracing
# echo "r:event1 sys_symlink" > kprobe_events
# echo "r:event2 sys_symlink" >> kprobe_events
# echo 1 > events/kprobes/enable
# ln -s /tmp/foo /tmp/bar

(without this patch)

# cat trace | grep -v ^#
ln-82 [000] dn.2 68.446525: event1: (kretprobe_trampoline+0x0/0x18 <- SyS_symlink)
ln-82 [000] dn.2 68.447831: event2: (ret_fast_syscall+0x0/0x1c <- SyS_symlink)

(with this patch)

# cat trace | grep -v ^#
ln-81 [000] dn.1 39.463469: event1: (ret_fast_syscall+0x0/0x1c <- SyS_symlink)
ln-81 [000] dn.1 39.464701: event2: (ret_fast_syscall+0x0/0x1c <- SyS_symlink)

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: KUMANO Syuhei <kumano.prog@gmail.com>
Signed-off-by: Jon Medhurst <tixy@linaro.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm/probes/kprobes/core.c | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)

--- a/arch/arm/probes/kprobes/core.c
+++ b/arch/arm/probes/kprobes/core.c
@@ -433,6 +433,7 @@ static __used __kprobes void *trampoline
struct hlist_node *tmp;
unsigned long flags, orig_ret_address = 0;
unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
+ kprobe_opcode_t *correct_ret_addr = NULL;

INIT_HLIST_HEAD(&empty_rp);
kretprobe_hash_lock(current, &head, &flags);
@@ -455,14 +456,34 @@ static __used __kprobes void *trampoline
/* another task is sharing our hash bucket */
continue;

+ orig_ret_address = (unsigned long)ri->ret_addr;
+
+ if (orig_ret_address != trampoline_address)
+ /*
+ * This is the real return address. Any other
+ * instances associated with this task are for
+ * other calls deeper on the call stack
+ */
+ break;
+ }
+
+ kretprobe_assert(ri, orig_ret_address, trampoline_address);
+
+ correct_ret_addr = ri->ret_addr;
+ hlist_for_each_entry_safe(ri, tmp, head, hlist) {
+ if (ri->task != current)
+ /* another task is sharing our hash bucket */
+ continue;
+
+ orig_ret_address = (unsigned long)ri->ret_addr;
if (ri->rp && ri->rp->handler) {
__this_cpu_write(current_kprobe, &ri->rp->kp);
get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
+ ri->ret_addr = correct_ret_addr;
ri->rp->handler(ri, regs);
__this_cpu_write(current_kprobe, NULL);
}

- orig_ret_address = (unsigned long)ri->ret_addr;
recycle_rp_inst(ri, &empty_rp);

if (orig_ret_address != trampoline_address)
@@ -474,7 +495,6 @@ static __used __kprobes void *trampoline
break;
}

- kretprobe_assert(ri, orig_ret_address, trampoline_address);
kretprobe_hash_unlock(current, &flags);

hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {

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