The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     2aebf5ee43bf0ed225a09a30cf515d9f2813b759
Gitweb:        https://git.kernel.org/tip/2aebf5ee43bf0ed225a09a30cf515d9f2813b759
Author:        Masami Hiramatsu (Google) <mhiramat@kernel.org>
AuthorDate:    Wed, 18 Jun 2025 09:05:23 +09:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 18 Jun 2025 13:59:56 +02:00

x86/alternatives: Fix int3 handling failure from broken text_poke array

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.

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")
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Link: https://lkml.kernel.org/r/\ 175020512308.3582717.13631440385506146631.stgit@mhiramat.tok.corp.google.com
---
 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 9ae80fa..ea1d984 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -3138,6 +3138,6 @@ 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();
 }