x86/kprobes: Drop removed INT3 handling code

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, it is already safe. The commit 5c02ece8
("x86/kprobes: Fix ordering while text-patching") introduced
text_poke_sync() to the arch_disarm_kprobe() right after removing INT3.
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.
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/166981518895.1131462.4693062055762912734.stgit@devnote3

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;