linux-kernel - Re: [PATCH 1/1] x86/fpu: x86/fpu: avoid math_state_restore() without used_math() in __restore_xstate

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Message-ID: <20150309143436.GA3526@redhat.com>
Date:	Mon, 9 Mar 2015 15:34:36 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Borislav Petkov <bp@...e.de>
Cc:	Dave Hansen <dave.hansen@...el.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pekka Riikonen <priikone@....fi>,
	Rik van Riel <riel@...hat.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>
Subject: Re: [PATCH 1/1] x86/fpu: x86/fpu: avoid math_state_restore()
	without used_math() in __restore_xstate_sig()

On 03/09, Borislav Petkov wrote:
>
> On Sat, Mar 07, 2015 at 04:38:44PM +0100, Oleg Nesterov wrote:
> > math_state_restore() assumes it is called with irqs disabled, but
> > this is not true if the caller is __restore_xstate_sig().
> >
> > This means that if ia32_fxstate == T and __copy_from_user() fails
> > __restore_xstate_sig() returns with irqs disabled too. This trgiggers
> >
> > 	BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:41
> > 	[<ffffffff81381499>] dump_stack+0x59/0xa0
> > 	[<ffffffff8106bd05>] ___might_sleep+0x105/0x110
> > 	[<ffffffff8138786d>] ? _raw_spin_unlock_irqrestore+0x3d/0x70
> > 	[<ffffffff8106bd8d>] __might_sleep+0x7d/0xb0
> > 	[<ffffffff81385426>] down_read+0x26/0xa0
> > 	[<ffffffff8138788a>] ? _raw_spin_unlock_irqrestore+0x5a/0x70
> > 	[<ffffffff81136038>] print_vma_addr+0x58/0x130
> > 	[<ffffffff8100239e>] signal_fault+0xbe/0xf0
> > 	[<ffffffff810419aa>] sys32_rt_sigreturn+0xba/0xd0
> >
> > Change __restore_xstate_sig() to call set_used_math() unconditionally,
> > this avoids sti/cli in math_state_restore(). If copy_from_user() fails
> > we can simply do fpu_finit() by hand.
> >
> > Note: this is only the first step. math_state_restore() should not check
> > used_math(), it should set this flag. While init_fpu() should simply die.
> >
> > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> > Cc: <stable@...r.kernel.org>
>
> Makes sense to me. I guess we should wait for Dave to test first though...

The patch only fixes the problem with irqs disabled, I tested this.

The problem with fpu_init/XRSTORS is another thing...

Oleg.

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