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Subject[PATCH] x86/kprobes: Fix to update kcb status flag after singlestepping
Date
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Fix kprobes to update kcb (kprobes control block) status flag to
KPROBE_HIT_SSDONE even if the kp->post_handler is not set.
This may cause a kernel panic if another int3 user runs right
after kprobes because kprobe_int3_handler() misunderstands the
int3 is kprobe's single stepping int3.

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Reported-by: Daniel Müller <deso@posteo.net>
Tested-by: Daniel Müller <deso@posteo.net>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20220727210136.jjgc3lpqeq42yr3m@muellerd-fedora-PC2BDTX9
---
arch/x86/kernel/kprobes/core.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 7c4ab8870da4..74167dc5f55e 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -814,16 +814,20 @@ set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
static void kprobe_post_process(struct kprobe *cur, struct pt_regs *regs,
struct kprobe_ctlblk *kcb)
{
- if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
- kcb->kprobe_status = KPROBE_HIT_SSDONE;
- cur->post_handler(cur, regs, 0);
- }
-
/* Restore back the original saved kprobes variables and continue. */
- if (kcb->kprobe_status == KPROBE_REENTER)
+ if (kcb->kprobe_status == KPROBE_REENTER) {
+ /* This will restore both kcb and current_kprobe */
restore_previous_kprobe(kcb);
- else
+ } else {
+ /*
+ * Always update the kcb status because
+ * reset_curent_kprobe() doesn't update kcb.
+ */
+ kcb->kprobe_status = KPROBE_HIT_SSDONE;
+ if (cur->post_handler)
+ cur->post_handler(cur, regs, 0);
reset_current_kprobe();
+ }
}
NOKPROBE_SYMBOL(kprobe_post_process);

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