linux-kernel - [PATCH v2 1/2] jump_label: Explicitly disable jump labels in _

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Message-Id: <eccf3cf668635c9b46acd6a4e3f57c05dbd8aa93.1518798288.git.jpoimboe@redhat.com>
Date:   Fri, 16 Feb 2018 10:31:14 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jason Baron <jbaron@...mai.com>, Borislav Petkov <bp@...e.de>
Subject: [PATCH v2 1/2] jump_label: Explicitly disable jump labels in __init code

After initmem has been freed, any jump label entries in __init code are
prevented from being written to by the kernel_text_address() check in
__jump_label_update().  However, this check is quite broad.  If
kernel_text_address() were to return false for any other reason, the
jump label write would fail silently with no warning.

For jump label entrieds in module init code, entry->code is set to zero
to indicate that the entry is disabled.  Do the same thing for core
kernel init code.  This makes the behavior more consistent, and will
also make it more straightforward to detect non-init jump label write
failures in the next patch.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 include/linux/jump_label.h |  3 +++
 init/main.c                |  2 ++
 kernel/jump_label.c        | 18 ++++++++++++++++--
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index b6a29c126cc4..2168cc6b8b30 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -151,6 +151,7 @@ extern struct jump_entry __start___jump_table[];
 extern struct jump_entry __stop___jump_table[];
 
 extern void jump_label_init(void);
+extern void jump_label_invalidate_init(void);
 extern void jump_label_lock(void);
 extern void jump_label_unlock(void);
 extern void arch_jump_label_transform(struct jump_entry *entry,
@@ -198,6 +199,8 @@ static __always_inline void jump_label_init(void)
 	static_key_initialized = true;
 }
 
+static inline void jump_label_invalidate_init(void) {}
+
 static __always_inline bool static_key_false(struct static_key *key)
 {
 	if (unlikely(static_key_count(key) > 0))
diff --git a/init/main.c b/init/main.c
index a8100b954839..969eaf140ef0 100644
--- a/init/main.c
+++ b/init/main.c
@@ -89,6 +89,7 @@
 #include <linux/io.h>
 #include <linux/cache.h>
 #include <linux/rodata_test.h>
+#include <linux/jump_label.h>
 
 #include <asm/io.h>
 #include <asm/bugs.h>
@@ -1000,6 +1001,7 @@ static int __ref kernel_init(void *unused)
 	/* need to finish all async __init code before freeing the memory */
 	async_synchronize_full();
 	ftrace_free_init_mem();
+	jump_label_invalidate_init();
 	free_initmem();
 	mark_readonly();
 	system_state = SYSTEM_RUNNING;
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index b4517095db6a..96274c6d3511 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -16,6 +16,7 @@
 #include <linux/jump_label_ratelimit.h>
 #include <linux/bug.h>
 #include <linux/cpu.h>
+#include <asm/sections.h>
 
 #ifdef HAVE_JUMP_LABEL
 
@@ -633,16 +634,29 @@ static void jump_label_del_module(struct module *mod)
 	}
 }
 
+/* Disable any jump label entries in __init code */
+void __init jump_label_invalidate_init(void)
+{
+	struct jump_entry *iter_start = __start___jump_table;
+	struct jump_entry *iter_stop = __stop___jump_table;
+	struct jump_entry *iter;
+
+	for (iter = iter_start; iter < iter_stop; iter++)
+		if (iter->code >= (unsigned long)_sinittext &&
+		    iter->code < (unsigned long)_einittext)
+			iter->code = 0;
+}
+
+/* Disable any jump label entries in module init code */
 static void jump_label_invalidate_module_init(struct module *mod)
 {
 	struct jump_entry *iter_start = mod->jump_entries;
 	struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 	struct jump_entry *iter;
 
-	for (iter = iter_start; iter < iter_stop; iter++) {
+	for (iter = iter_start; iter < iter_stop; iter++)
 		if (within_module_init(iter->code, mod))
 			iter->code = 0;
-	}
 }
 
 static int
-- 
2.14.3