linux-kernel - Re: [PATCH 6/9] s390/bug: Implement __WARN

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20251209144200.15189D45-hca@linux.ibm.com>
Date: Tue, 9 Dec 2025 15:42:00 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Mark Rutland <mark.rutland@....com>, Arnd Bergmann <arnd@...db.de>,
        Jens Remus <jremus@...ux.ibm.com>,
        Stefan Schulze Frielinghaus <stefansf@...ux.ibm.com>,
        Juergen Christ <jchrist@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH 6/9] s390/bug: Implement __WARN_printf()

On Tue, Dec 09, 2025 at 01:35:40PM +0100, Peter Zijlstra wrote:
> On Tue, Dec 09, 2025 at 01:16:58PM +0100, Heiko Carstens wrote:
> > +#define __WARN_print_arg(flags, format, arg...)				\
> > +do {									\
> > +	int __flags = (flags) | BUGFLAG_WARNING | BUGFLAG_ARGS;		\
> > +									\
> > +	__WARN_trap(__WARN_bug_entry(__flags, format), ## arg);		\
> > +} while (0)
> 
> So on x86 I had to add:
> 
> 	asm("");
> 
> after the __WARN_trap() call above, to inhibit tail call optimization,
> because:
> 
> > +void *__warn_args(struct arch_va_list *args, struct pt_regs *regs)
> > +{
> > +	struct stack_frame *stack_frame;
...
> > +	stack_frame = (struct stack_frame *)regs->gprs[15];
> > +	args->__overflow_arg_area = stack_frame + 1;
> > +	args->__reg_save_area = regs->gprs;
> > +	args->__gpr = 1;
> > +	return args;
> > +}
> 
> that would affect the stack layout here. You don't suffer this because
> you have a link register like setup?

Yes, in case of tail call optimization everything which needs to be known to
setup va_list is passed in registers. __overflow_arg_area will then point to
garbage, but it doesn't matter since it is unused for such cases.