linux-kernel - Re: [PATCH] x86/math64: handle #DE in mul_u64_u64_div

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

Message-ID: <20250724135840.GA19593@redhat.com>
Date: Thu, 24 Jul 2025 15:58:40 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: David Laight <david.laight.linux@...il.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Li,Rongqing" <lirongqing@...du.com>,
	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH] x86/math64: handle #DE in mul_u64_u64_div_u64()

On 07/24, David Laight wrote:
>
> On Thu, 24 Jul 2025 10:25:48 +0200
> Oleg Nesterov <oleg@...hat.com> wrote:
>
> > --- a/arch/x86/mm/extable.c
> > +++ b/arch/x86/mm/extable.c
> > @@ -38,6 +38,9 @@ static bool ex_handler_default(const struct exception_table_entry *e,
> >  	if (e->data & EX_FLAG_CLEAR_DX)
> >  		regs->dx = 0;
> >
> > +	if (e->data & EX_FLAG_XXX_AX)
> > +		regs->ax = -1ul;
>
> That would need to set %eax to a 64bit ~0u;
> I don't think the above would sign extend the value.

Hmm... could you spell please?

pt_regs->ax is always 'unsigned long', regardless of bitness...

> Makes me think - always bad.
> I wonder how hard it would be to implement EX_FLAG_WARN_ONCE.
> Mostly it would need a writeable bitmap with one bit for each
> extable entry.

Would be nice... But who else will use this feature ? ;) I mean, it needs
some justification.

Oleg.