linux-kernel - [PATCH] x86: alternative: Fix int3 handling failure from broken text

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Message-ID:  <175020512308.3582717.13631440385506146631.stgit@mhiramat.tok.corp.google.com>
Date: Wed, 18 Jun 2025 09:05:23 +0900
From: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	x86@...nel.org,
	Naresh Kamboju <naresh.kamboju@...aro.org>,
	open list <linux-kernel@...r.kernel.org>,
	Linux trace kernel <linux-trace-kernel@...r.kernel.org>,
	lkft-triage@...ts.linaro.org,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Arnd Bergmann <arnd@...db.de>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Anders Roxell <anders.roxell@...aro.org>
Subject: [PATCH] x86: alternative: Fix int3 handling failure from broken text_poke array

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

Since smp_text_poke_single() does not expect there is another
text_poke request is queued, it can make text_poke_array not
sorted or cause a buffer overflow on the text_poke_array.vec[].
This will cause an Oops in int3 because of bsearch failing;


   CPU 0                        CPU 1                      CPU 2
   -----                        -----                      -----

 smp_text_poke_batch_add()

			    smp_text_poke_single() <<-- Adds out of order

							<int3>
                                                	[Fails o find address
                                                        in text_poke_array ]
                                                        OOPS!

Or unhandled page fault because of a buffer overflow;


   CPU 0                        CPU 1
   -----                        -----

 smp_text_poke_batch_add() <<+
 ...                         |
 smp_text_poke_batch_add() <<-- Adds TEXT_POKE_ARRAY_MAX times.

			     smp_text_poke_single() {
			     	__smp_text_poke_batch_add() <<-- Adds entry at
								TEXT_POKE_ARRAY_MAX + 1

                		smp_text_poke_batch_finish()
                        	  [Unhandled page fault because
				   text_poke_array.nr_entries is
				   overwritten]
				   BUG!
			     }


Use smp_text_poke_batch_add() instead of __smp_text_poke_batch_add()
so that it correctly flush the queue if needed.

Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
Closes: https://lore.kernel.org/all/CA+G9fYsLu0roY3DV=tKyqP7FEKbOEETRvTDhnpPxJGbA=Cg+4w@mail.gmail.com/
Fixes: c8976ade0c1b ("x86/alternatives: Simplify smp_text_poke_single() by using tp_vec and existing APIs")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
Tested-by: Linux Kernel Functional Testing <lkft@...aro.org>
---
 arch/x86/kernel/alternative.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index ecfe7b497cad..8038951650c6 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -3107,6 +3107,6 @@ void __ref smp_text_poke_batch_add(void *addr, const void *opcode, size_t len, c
  */
 void __ref smp_text_poke_single(void *addr, const void *opcode, size_t len, const void *emulate)
 {
-	__smp_text_poke_batch_add(addr, opcode, len, emulate);
+	smp_text_poke_batch_add(addr, opcode, len, emulate);
 	smp_text_poke_batch_finish();
 }