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authorZhou Chengming <zhouchengming1@huawei.com>2017-11-02 09:18:21 +0800
committerIngo Molnar <mingo@kernel.org>2017-11-07 12:20:09 +0100
commite846d13958066828a9483d862cc8370a72fadbb6 (patch)
tree4ee0e7c3f4b1eec670b0edf57dac66e201f49658 /kernel/extable.c
parentd786f05175fae09cc39dfa5769c62649341caeb4 (diff)
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kprobes, x86/alternatives: Use text_mutex to protect smp_alt_modules
We use alternatives_text_reserved() to check if the address is in the fixed pieces of alternative reserved, but the problem is that we don't hold the smp_alt mutex when call this function. So the list traversal may encounter a deleted list_head if another path is doing alternatives_smp_module_del(). One solution is that we can hold smp_alt mutex before call this function, but the difficult point is that the callers of this functions, arch_prepare_kprobe() and arch_prepare_optimized_kprobe(), are called inside the text_mutex. So we must hold smp_alt mutex before we go into these arch dependent code. But we can't now, the smp_alt mutex is the arch dependent part, only x86 has it. Maybe we can export another arch dependent callback to solve this. But there is a simpler way to handle this problem. We can reuse the text_mutex to protect smp_alt_modules instead of using another mutex. And all the arch dependent checks of kprobes are inside the text_mutex, so it's safe now. Signed-off-by: Zhou Chengming <zhouchengming1@huawei.com> Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: bp@suse.de Fixes: 2cfa197 "ftrace/alternatives: Introducing *_text_reserved functions" Link: http://lkml.kernel.org/r/1509585501-79466-1-git-send-email-zhouchengming1@huawei.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/extable.c')
-rw-r--r--kernel/extable.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/extable.c b/kernel/extable.c
index 9aa1cc41ecf7..a17fdb63dc3e 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -31,6 +31,8 @@
* mutex protecting text section modification (dynamic code patching).
* some users need to sleep (allocating memory...) while they hold this lock.
*
+ * Note: Also protects SMP-alternatives modification on x86.
+ *
* NOT exported to modules - patching kernel text is a really delicate matter.
*/
DEFINE_MUTEX(text_mutex);