linux-kernel - Re: [PATCH 11/20] signal/s390: Use force_sigsegv in default_trap

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Date:   Tue, 26 Oct 2021 11:38:44 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org
Cc:     linux-arch@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>, linux-s390@...r.kernel.org
Subject: Re: [PATCH 11/20] signal/s390: Use force_sigsegv in
 default_trap_handler

Am 20.10.21 um 19:43 schrieb Eric W. Biederman:
> Reading the history it is unclear why default_trap_handler calls
> do_exit.  It is not even menthioned in the commit where the change
> happened.  My best guess is that because it is unknown why the
> exception happened it was desired to guarantee the process never
> returned to userspace.
> 
> Using do_exit(SIGSEGV) has the problem that it will only terminate one
> thread of a process, leaving the process in an undefined state.
> 
> Use force_sigsegv(SIGSEGV) instead which effectively has the same
> behavior except that is uses the ordinary signal mechanism and
> terminates all threads of a process and is generally well defined.

Do I get that right, that programs can not block SIGSEGV from force_sigsegv
with a signal handler? Thats how I read the code. If this is true
then

Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>
> 
> Cc: Heiko Carstens <hca@...ux.ibm.com>
> Cc: Vasily Gorbik <gor@...ux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@...ibm.com>
> Cc: linux-s390@...r.kernel.org
> Fixes: ca2ab03237ec ("[PATCH] s390: core changes")
> History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---
>   arch/s390/kernel/traps.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/s390/kernel/traps.c b/arch/s390/kernel/traps.c
> index bcefc2173de4..51729ea2cf8e 100644
> --- a/arch/s390/kernel/traps.c
> +++ b/arch/s390/kernel/traps.c
> @@ -84,7 +84,7 @@ static void default_trap_handler(struct pt_regs *regs)
>   {
>   	if (user_mode(regs)) {
>   		report_user_fault(regs, SIGSEGV, 0);
> -		do_exit(SIGSEGV);
> +		force_sigsegv(SIGSEGV);
>   	} else
>   		die(regs, "Unknown program exception");
>   }
>