From fd4363fff3d96795d3feb1b3fb48ce590f186bdd Mon Sep 17 00:00:00 2001 From: Jiri Kosina Date: Fri, 12 Jul 2013 11:21:48 +0200 Subject: x86: Introduce int3 (breakpoint)-based instruction patching Introduce a method for run-time instruction patching on a live SMP kernel based on int3 breakpoint, completely avoiding the need for stop_machine(). The way this is achieved: - add a int3 trap to the address that will be patched - sync cores - update all but the first byte of the patched range - sync cores - replace the first byte (int3) by the first byte of replacing opcode - sync cores According to http://lkml.indiana.edu/hypermail/linux/kernel/1001.1/01530.html synchronization after replacing "all but first" instructions should not be necessary (on Intel hardware), as the syncing after the subsequent patching of the first byte provides enough safety. But there's not only Intel HW out there, and we'd rather be on a safe side. If any CPU instruction execution would collide with the patching, it'd be trapped by the int3 breakpoint and redirected to the provided "handler" (which would typically mean just skipping over the patched region, acting as "nop" has been there, in case we are doing nop -> jump and jump -> nop transitions). Ftrace has been using this very technique since 08d636b ("ftrace/x86: Have arch x86_64 use breakpoints instead of stop machine") for ages already, and jump labels are another obvious potential user of this. Based on activities of Masami Hiramatsu a few years ago. Reviewed-by: Steven Rostedt Reviewed-by: Masami Hiramatsu Signed-off-by: Jiri Kosina Link: http://lkml.kernel.org/r/alpine.LNX.2.00.1307121102440.29788@pobox.suse.cz Signed-off-by: H. Peter Anvin --- kernel/kprobes.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/kprobes.c b/kernel/kprobes.c index 6e33498d665c..b58b490fa439 100644 --- a/kernel/kprobes.c +++ b/kernel/kprobes.c @@ -1709,7 +1709,7 @@ EXPORT_SYMBOL_GPL(unregister_kprobes); static struct notifier_block kprobe_exceptions_nb = { .notifier_call = kprobe_exceptions_notify, - .priority = 0x7fffffff /* we need to be notified first */ + .priority = 0x7ffffff0 /* High priority, but not first. */ }; unsigned long __weak arch_deref_entry_point(void *entry) -- cgit v1.2.3