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Date: Thu, 16 Apr 2015 20:20:37 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Rik van Riel <riel@redhat.com>, Andy Lutomirski <luto@amacapital.net>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tavis Ormandy <taviso@google.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] x86/fpu: Load xsave pointer *after* initialization
Message-ID: <20150416182037.GA26537@redhat.com>
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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.