Messages in this thread Patch in this message | | | Date | Tue, 19 Nov 2019 16:56:46 -0000 | From | "tip-bot2 for Peter Zijlstra" <> | Subject | [tip: core/kprobes] x86/kprobe: Add comments to arch_{,un}optimize_kprobes() |
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The following commit has been merged into the core/kprobes branch of tip:
Commit-ID: 654920255149b034ad5a8aee6b02cfa16e65e9c0 Gitweb: https://git.kernel.org/tip/654920255149b034ad5a8aee6b02cfa16e65e9c0 Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Mon, 11 Nov 2019 14:02:10 +01:00 Committer: Ingo Molnar <mingo@kernel.org> CommitterDate: Tue, 19 Nov 2019 13:13:08 +01:00
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 <ast@kernel.org> Tested-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Alexei Starovoitov <ast@kernel.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: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/20191111132458.401696663@infradead.org Signed-off-by: Ingo Molnar <mingo@kernel.org> --- arch/x86/kernel/kprobes/opt.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c index 26e0d6c..3f45b5c 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);
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