linux-kernel - [PATCH -tip v2] x86/kprobes: Drop removed INT3 handling code

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Date:   Wed, 30 Nov 2022 22:33:09 +0900
From:   "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To:     x86@...nel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        Jinyang He <hejinyang@...ngson.cn>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>
Subject: [PATCH -tip v2] x86/kprobes: Drop removed INT3 handling code

From: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Drop removed INT3 handling code from kprobe_int3_handler() because this
case (get_kprobe() doesn't return corresponding kprobe AND the INT3 is
removed) must not happen with the kprobe managed INT3, but can happen
with the non-kprobe INT3, which should be handled by other callbacks.

For the kprobe managed INT3, it is already safe. The commit 5c02ece81848d
("x86/kprobes: Fix ordering while text-patching") introduced
text_poke_sync() to the arch_disarm_kprobe() right after removing INT3.
Since this text_poke_sync() uses IPI to call sync_core() on all online
cpus, that ensures that all running INT3 exception handlers have done.
And, the unregister_kprobe() will remove the kprobe from the hash table
after arch_disarm_kprobe().

Thus, when the kprobe managed INT3 hits, kprobe_int3_handler() should
be able to find corresponding kprobe always by get_kprobe(). If it can
not find any kprobe, this means that is NOT a kprobe managed INT3.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 Changes in v2:
  - update comment to mention that the first safe commit.
---
 arch/x86/kernel/kprobes/core.c |   14 --------------
 1 file changed, 14 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 66299682b6b7..33390ed4dcf3 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -986,20 +986,6 @@ int kprobe_int3_handler(struct pt_regs *regs)
 			kprobe_post_process(p, regs, kcb);
 			return 1;
 		}
-	}
-
-	if (*addr != INT3_INSN_OPCODE) {
-		/*
-		 * The breakpoint instruction was removed right
-		 * after we hit it.  Another cpu has removed
-		 * either a probepoint or a debugger breakpoint
-		 * at this address.  In either case, no further
-		 * handling of this interrupt is appropriate.
-		 * Back up over the (now missing) int3 and run
-		 * the original instruction.
-		 */
-		regs->ip = (unsigned long)addr;
-		return 1;
 	} /* else: not a kprobe fault; let the kernel handle it */

 	return 0;