signal: Properly deliver SIGILL from uprobes

[ Upstream commit 55a3235f ]

For userspace to tell the difference between a random signal and an
exception, the exception must include siginfo information.

Using SEND_SIG_FORCED for SIGILL is thus wrong, and it will result
in userspace seeing si_code == SI_USER (like a random signal) instead
of si_code == SI_KERNEL or a more specific si_code as all exceptions
deliver.

Therefore replace force_sig_info(SIGILL, SEND_SIG_FORCE, current)
with force_sig(SIG_ILL, current) which gets this right and is
shorter and easier to type.

Fixes: 014940ba ("uprobes/x86: Send SIGILL if arch_uprobe_post_xol() fails")
Fixes: 0b5256c7 ("uprobes: Send SIGILL if handle_trampoline() fails")
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

kernel/events/uprobes.c

@@ -1858,7 +1858,7 @@ static void handle_trampoline(struct pt_regs *regs)
 
  sigill:
 	uprobe_warn(current, "handle uretprobe, sending SIGILL.");
-	force_sig_info(SIGILL, SEND_SIG_FORCED, current);
+	force_sig(SIGILL, current);
 
 }
 
@@ -1974,7 +1974,7 @@ static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
 
 	if (unlikely(err)) {
 		uprobe_warn(current, "execute the probed insn, sending SIGILL.");
-		force_sig_info(SIGILL, SEND_SIG_FORCED, current);
+		force_sig(SIGILL, current);
 	}
 }