linux-kernel - [tip: perf/urgent] x86/kprobes: Update kcb status flag after singlestepping

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Date:   Tue, 02 Aug 2022 11:03:06 -0000
From:   "tip-bot2 for Masami Hiramatsu (Google)" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     deso@...teo.net, "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, stable@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] x86/kprobes: Update kcb status flag after singlestepping

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     dec8784c9088b131a1523f582c2194cfc8107dc0
Gitweb:        https://git.kernel.org/tip/dec8784c9088b131a1523f582c2194cfc8107dc0
Author:        Masami Hiramatsu (Google) <mhiramat@...nel.org>
AuthorDate:    Tue, 02 Aug 2022 15:04:16 +09:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Tue, 02 Aug 2022 12:35:04 +02:00

x86/kprobes: Update kcb status flag after singlestepping

Fix kprobes to update kcb (kprobes control block) status flag to
KPROBE_HIT_SSDONE even if the kp->post_handler is not set.

This bug 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@...teo.net>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Tested-by: Daniel Müller <deso@...teo.net>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/all/20220727210136.jjgc3lpqeq42yr3m@muellerd-fedora-PC2BDTX9
Link: https://lore.kernel.org/r/165942025658.342061.12452378391879093249.stgit@devnote2
---
 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 7c4ab88..74167dc 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);