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SubjectRe: [PATCH -tip] x86/kprobes: Drop removed INT3 handling code
On Fri, 25 Nov 2022 23:44:47 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>
> Drop removed INT3 handling code from kprobe_int3_handler() because this
> case (get_kprobe() doesn't return corresponding kprobe AND the INT3 is
> removed) must not happen with the kprobe managed INT3, but can happen
> with the non-kprobe INT3, which should be handled by other callbacks.
>
> For the kprobe managed INT3, the arch_disarm_kprobe() removes the INT3
> and then calls text_poke_sync(). Since this text_poke_sync() uses IPI
> to call sync_core() on all online cpus, that ensures that all running
> INT3 exception handlers have done.
> And, the unregister_kprobe() will remove the kprobe from the hash table
> after arch_disarm_kprobe().
>
> Thus, when the kprobe managed INT3 hits, kprobe_int3_handler() should
> be able to find corresponding kprobe always by get_kprobe(). If it can
> not find any kprobe, this means that is NOT a kprobe managed INT3.
>

I believe this was fixed by:

5c02ece81848d ("x86/kprobes: Fix ordering while text-patching")

That should be mentioned in the commit log.

Anyway, looks good.

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve



> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
> arch/x86/kernel/kprobes/core.c | 14 --------------
> 1 file changed, 14 deletions(-)
>
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 66299682b6b7..33390ed4dcf3 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -986,20 +986,6 @@ int kprobe_int3_handler(struct pt_regs *regs)
> kprobe_post_process(p, regs, kcb);
> return 1;
> }
> - }
> -
> - if (*addr != INT3_INSN_OPCODE) {
> - /*
> - * The breakpoint instruction was removed right
> - * after we hit it. Another cpu has removed
> - * either a probepoint or a debugger breakpoint
> - * at this address. In either case, no further
> - * handling of this interrupt is appropriate.
> - * Back up over the (now missing) int3 and run
> - * the original instruction.
> - */
> - regs->ip = (unsigned long)addr;
> - return 1;
> } /* else: not a kprobe fault; let the kernel handle it */
>
> return 0;

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