diff options
author | Peter Zijlstra <[email protected]> | 2019-11-11 14:02:10 +0100 |
---|---|---|
committer | Ingo Molnar <[email protected]> | 2019-11-27 07:44:25 +0100 |
commit | f2cb4f95b7571f2bebcf226cd92b448fd58950ca (patch) | |
tree | 90fdcc1b05666267186ea47bd45fc7c3f71e0c6b | |
parent | 04ae87a52074e2d448fc66143f1bd2c7d694d2b9 (diff) |
x86/kprobe: Add comments to arch_{,un}optimize_kprobes()
Add a few words describing how it is safe to overwrite the 4 bytes
after a kprobe. In specific it is possible the JMP.d32 required for
the optimized kprobe overwrites multiple instructions.
Tested-by: Alexei Starovoitov <[email protected]>
Tested-by: Steven Rostedt (VMware) <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Alexei Starovoitov <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
-rw-r--r-- | arch/x86/kernel/kprobes/opt.c | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c index 26e0d6c4d8d6..3f45b5c43a71 100644 --- a/arch/x86/kernel/kprobes/opt.c +++ b/arch/x86/kernel/kprobes/opt.c @@ -414,8 +414,12 @@ err: } /* - * Replace breakpoints (int3) with relative jumps. + * Replace breakpoints (INT3) with relative jumps (JMP.d32). * Caller must call with locking kprobe_mutex and text_mutex. + * + * The caller will have installed a regular kprobe and after that issued + * syncrhonize_rcu_tasks(), this ensures that the instruction(s) that live in + * the 4 bytes after the INT3 are unused and can now be overwritten. */ void arch_optimize_kprobes(struct list_head *oplist) { @@ -441,7 +445,13 @@ void arch_optimize_kprobes(struct list_head *oplist) } } -/* Replace a relative jump with a breakpoint (int3). */ +/* + * Replace a relative jump (JMP.d32) with a breakpoint (INT3). + * + * After that, we can restore the 4 bytes after the INT3 to undo what + * arch_optimize_kprobes() scribbled. This is safe since those bytes will be + * unused once the INT3 lands. + */ void arch_unoptimize_kprobe(struct optimized_kprobe *op) { arch_arm_kprobe(&op->kp); |