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Date: Thu, 25 Apr 2019 17:11:41 -0700
From: Nadav Amit <namit@...are.com>
To: Peter Zijlstra <peterz@...radead.org>, Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <x86@...nel.org>, <hpa@...or.com>, Thomas
 Gleixner <tglx@...utronix.de>, Nadav Amit <nadav.amit@...il.com>, Dave Hansen
	<dave.hansen@...ux.intel.com>, <linux_dti@...oud.com>,
	<linux-integrity@...r.kernel.org>, <linux-security-module@...r.kernel.org>,
	<akpm@...ux-foundation.org>, <kernel-hardening@...ts.openwall.com>,
	<linux-mm@...ck.org>, <will.deacon@....com>, <ard.biesheuvel@...aro.org>,
	<kristen@...ux.intel.com>, <deneen.t.dock@...el.com>, Rick Edgecombe
	<rick.p.edgecombe@...el.com>, Nadav Amit <namit@...are.com>, Masami Hiramatsu
	<mhiramat@...nel.org>
Subject: [PATCH v5 21/23] x86/alternative: Comment about module removal races

Add a comment to clarify that users of text_poke() must ensure that
no races with module removal take place.

Cc: Masami Hiramatsu <mhiramat@...nel.org>
Signed-off-by: Nadav Amit <namit@...are.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
---
 arch/x86/kernel/alternative.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 18f959975ea0..7b9b49dfc05a 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -810,6 +810,11 @@ static void *__text_poke(void *addr, const void *opcode, size_t len)
  * It means the size must be writable atomically and the address must be aligned
  * in a way that permits an atomic write. It also makes sure we fit on a single
  * page.
+ *
+ * Note that the caller must ensure that if the modified code is part of a
+ * module, the module would not be removed during poking. This can be achieved
+ * by registering a module notifier, and ordering module removal and patching
+ * trough a mutex.
  */
 void *text_poke(void *addr, const void *opcode, size_t len)
 {
-- 
2.17.1

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