linux-kernel - Re: [PATCH] x86/fpu: Load xsave pointer *after* initialization

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Message-ID: <20150416182037.GA26537@redhat.com>
Date:	Thu, 16 Apr 2015 20:20:37 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tavis Ormandy <taviso@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/fpu: Load xsave pointer *after* initialization

On 04/16, Borislav Petkov wrote:
>
> Box exploded with the splat at the end because we do cache
> &target->thread.fpu.state->xsave into the local variable xsave but
> that pointer is NULL at that time and it gets initialized later, in
> init_fpu(), see
> 
> 	e7f180dcd8ab ("x86/fpu: Change xstateregs_get()/set() to use
> 		      ->xsave.i387 rather than ->fxsave")

OOPS! thanks a lot!!!

> --- a/arch/x86/kernel/i387.c
> +++ b/arch/x86/kernel/i387.c
> @@ -341,7 +341,7 @@ int xstateregs_get(struct task_struct *target, const struct user_regset *regset,
>  		unsigned int pos, unsigned int count,
>  		void *kbuf, void __user *ubuf)
>  {
> -	struct xsave_struct *xsave = &target->thread.fpu.state->xsave;
> +	struct xsave_struct *xsave;
>  	int ret;
>  
>  	if (!cpu_has_xsave)
> @@ -351,6 +351,8 @@ int xstateregs_get(struct task_struct *target, const struct user_regset *regset,
>  	if (ret)
>  		return ret;
>  
> +	xsave = &target->thread.fpu.state->xsave;
> +

Yes, but don't we need the same change in xstateregs_set() ?

Oleg.

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