linux-kernel - Re: [PATCH 17/20] signal/x86: In emulate_vsyscall force a signal instead of calling do

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Date:   Thu, 21 Oct 2021 09:36:44 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 17/20] signal/x86: In emulate_vsyscall force a signal
 instead of calling do_exit

On Wed, Oct 20, 2021 at 12:44:03PM -0500, Eric W. Biederman wrote:
> Directly calling do_exit with a signal number has the problem that
> all of the side effects of the signal don't happen, such as
> killing all of the threads of a process instead of just the
> calling thread.
> 
> So replace do_exit(SIGSYS) with force_fatal_sig(SIGSYS) which
> causes the signal handling to take it's normal path and work
> as expected.
> 
> Cc: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---
>  arch/x86/entry/vsyscall/vsyscall_64.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
> index 1b40b9297083..0b6b277ee050 100644
> --- a/arch/x86/entry/vsyscall/vsyscall_64.c
> +++ b/arch/x86/entry/vsyscall/vsyscall_64.c
> @@ -226,7 +226,8 @@ bool emulate_vsyscall(unsigned long error_code,
>  	if ((!tmp && regs->orig_ax != syscall_nr) || regs->ip != address) {
>  		warn_bad_vsyscall(KERN_DEBUG, regs,
>  				  "seccomp tried to change syscall nr or ip");
> -		do_exit(SIGSYS);
> +		force_fatal_sig(SIGSYS);
> +		return true;
>  	}
>  	regs->orig_ax = -1;
>  	if (tmp)

This looks correct to me, but please double-check the x86 selftests if
you haven't already.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook