linux-kernel - Re: [PATCH 2/3] x86, xsave: remove thread_has_fpu() bug check in __sanitize_i387

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: <20120509203047.GA334@redhat.com>
Date:	Wed, 9 May 2012 22:30:47 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	torvalds@...ux-foundation.org, hpa@...or.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org, suresh@...stanetworks.com
Subject: Re: [PATCH 2/3] x86, xsave: remove thread_has_fpu() bug check in
	__sanitize_i387_state()

Hi Suresh,

I can't really comment this series, my understanding of this code
is too limited.

But could you explain this patch? I am just curious.

On 05/08, Suresh Siddha wrote:
>
> BUG_ON() in __sanitize_i387_state() is checking that the fpu state
> is not live any more. But for preempt kernels, task can be scheduled
> out and in at any place and the preload_fpu logic during context switch
> can make the fpu registers live again.

And? Do you see any particular scenario when this BUG_ON() is wrong?

Afaics, __sanitize_i387_state() should not be called if the task can
be scheduled in with ->fpu_counter != 0.

> Similarly during core dump, thread dumping the core can schedule out
> and in for page-allocations etc in non-preempt case.

Again, can't understand. The core-dumping thread does init_fpu()
before it calls sanitize_i387_state().

Oleg.

--
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/