[musl] [PATCH] [stable v4.1] arm64: Remove unimplemented syscall log message

[musl] [PATCH] [stable v4.1] arm64: Remove unimplemented syscall log message

[Arnd Bergmann]

From: Michael Weiser <michael.weiser@gmx.de>

commit 1962682d2b2fbe6cfa995a85c53c069fadda473e upstream.

Stop printing a (ratelimited) kernel message for each instance of an
unimplemented syscall being called. Userland making an unimplemented
syscall is not necessarily misbehaviour and to be expected with a
current userland running on an older kernel. Also, the current message
looks scary to users but does not actually indicate a real problem nor
help them narrow down the cause. Just rely on sys_ni_syscall() to return
-ENOSYS.

Cc: <stable@vger.kernel.org>
Cc: Martin Vajnar <martin.vajnar@gmail.com>
Cc: musl@lists.openwall.com
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Michael Weiser <michael.weiser@gmx.de>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
This was backported to v4.14 and later, but is missing in v4.4 and
before, apparently because of a trivial merge conflict. This is
a manual backport I did after I saw a report about the issue
by Martin Vajnar on the musl mailing list.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/arm64/kernel/traps.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 9322be69ca09..db4163808c76 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -363,14 +363,6 @@ asmlinkage long do_ni_syscall(struct pt_regs *regs)
 	}
 #endif
 
-	if (show_unhandled_signals && printk_ratelimit()) {
-		pr_info("%s[%d]: syscall %d\n", current->comm,
-			task_pid_nr(current), (int)regs->syscallno);
-		dump_instr("", regs);
-		if (user_mode(regs))
-			__show_regs(regs);
-	}
-
 	return sys_ni_syscall();
 }
 
-- 
2.29.2

Re: [musl] [PATCH] [stable v4.1] arm64: Remove unimplemented syscall log message

[Arnd Bergmann]

On Wed, Jun 2, 2021 at 1:48 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Michael Weiser <michael.weiser@gmx.de>
>
> commit 1962682d2b2fbe6cfa995a85c53c069fadda473e upstream.
>
> Stop printing a (ratelimited) kernel message for each instance of an
> unimplemented syscall being called. Userland making an unimplemented
> syscall is not necessarily misbehaviour and to be expected with a
> current userland running on an older kernel. Also, the current message
> looks scary to users but does not actually indicate a real problem nor
> help them narrow down the cause. Just rely on sys_ni_syscall() to return
> -ENOSYS.

Nevermind, I forgot the 4.1.y line had ended. The 4.4 version is still needed
though, and also applies to 4.9.

        Arnd