linux-kernel - [PATCH v3 10/10] x86/module: Use text_mutex in apply_relocate

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Date:   Sat, 25 Apr 2020 06:07:30 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     live-patching@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Jessica Yu <jeyu@...nel.org>,
        Joe Lawrence <joe.lawrence@...hat.com>
Subject: [PATCH v3 10/10] x86/module: Use text_mutex in apply_relocate_add()

Now that the livepatch code no longer needs the text_mutex for changing
module permissions, move its usage down to apply_relocate_add().

Note the s390 version of apply_relocate_add() doesn't need to use the
text_mutex because it already uses s390_kernel_write_lock, which
accomplishes the same task.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/kernel/module.c | 9 +++++++--
 kernel/livepatch/core.c  | 6 ------
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index 7614f478fd7a..23c95a53d20e 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -18,6 +18,7 @@
 #include <linux/gfp.h>
 #include <linux/jump_label.h>
 #include <linux/random.h>
+#include <linux/memory.h>
 
 #include <asm/text-patching.h>
 #include <asm/page.h>
@@ -227,14 +228,18 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 	bool early = me->state == MODULE_STATE_UNFORMED;
 	void *(*write)(void *, const void *, size_t) = memcpy;
 
-	if (!early)
+	if (!early) {
 		write = text_poke;
+		mutex_lock(&text_mutex);
+	}
 
 	ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
 				   write);
 
-	if (!early)
+	if (!early) {
 		text_poke_sync();
+		mutex_unlock(&text_mutex);
+	}
 
 	return ret;
 }
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 6b8b3c067be0..96d2da14eb0d 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -775,9 +775,6 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 	int ret;
 
 	if (klp_is_module(obj)) {
-
-		mutex_lock(&text_mutex);
-
 		/*
 		 * Only write module-specific relocations here
 		 * (.klp.rela.{module}.*).  vmlinux-specific relocations were
@@ -785,9 +782,6 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 		 * itself.
 		 */
 		ret = klp_apply_object_relocs(patch, obj);
-
-		mutex_unlock(&text_mutex);
-
 		if (ret)
 			return ret;
 	}
-- 
2.21.1