linux-kernel - Re: [PATCH v3 3/3] sched, x86: Check that we're on the right stack in schedule and __might

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: <CALCETrVJJUcPRfkWRouLJCNUVNRH3aWX0X_K8L62yrUu1aR8Vg@mail.gmail.com>
Date:	Wed, 19 Nov 2014 15:49:29 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>, Borislav Petkov <bp@...en8.de>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v3 3/3] sched, x86: Check that we're on the right stack in
 schedule and __might_sleep

On Wed, Nov 19, 2014 at 3:23 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Wed, Nov 19, 2014 at 3:04 PM, Andy Lutomirski <luto@...capital.net> wrote:
>>
>> Does that include nmi?  I'm a bit afraid of touching that code.
>
> NMI is kind of special, since it's really not supposed to touch
> 'current' or anything like that, and that's how we do preempt-count
> (and that's where irq-count is) right now.
>
> I would prefer to have preempt_count be a percpu variable rather than
> a per-thread one, but there are historical reasons for that horror. Oh
> well.
>
>> It's certainly easy enough to bump irq_count in the paranoid entries.
>
> It definitely shouldn't be done from the assembly code. Usually it's
> "irq_enter/exit()" that does it, but for NMI you'd presumably just do
> it explicitly from do_nmi() or similar. But NMI really is nastier than
> other cases, see above.

My only real objection is that it's going to be ugly and error prone.
It'll have to be something like:

if (!user_mode_vm(regs))
    irq_enter();

...

if (!user_mode_vm(regs))
    irq_exit();

because the whole point of this series is to make the IST entries not
be atomic when they come from userspace.  We can wrap this in an
inline cond_ist_enter/cond_ist_exit or whatever, but still, blech.

Tony already sent the follow-up patch that will make do_machine_check
enable interrupts if it came from userspace.

--Andy

>
> (That said, I thought we did it anyway, but now that I look I can't
> find it. So I was probably just smoking something)
>
>              Linus



-- 
Andy Lutomirski
AMA Capital Management, LLC
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/