linux-kernel - Re: [patch V2 12/52] x86/fpu: Fail ptrace() requests that try to set invalid MXCSR values

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Date:   Wed, 16 Jun 2021 17:31:38 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [patch V2 12/52] x86/fpu: Fail ptrace() requests that try to set
 invalid MXCSR values

On Mon, Jun 14, 2021 at 05:44:20PM +0200, Thomas Gleixner wrote:
> From: Andy Lutomirski <luto@...nel.org>
> 
> We're not doing anyone any favors by accepting and silently changing an
> invalid MXCSR value supplied via ptrace().  Instead, return -EINVAL on
> invalid input.
> 
> If this breaks something, we can revert it.

Please use passive voice in your commit message: no "we" or "I", etc,

> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
> V2: New patch. Picked up from Andy.
> ---
>  arch/x86/kernel/fpu/regset.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> ---
> --- a/arch/x86/kernel/fpu/regset.c
> +++ b/arch/x86/kernel/fpu/regset.c
> @@ -65,8 +65,9 @@ int xfpregs_set(struct task_struct *targ
>  	if (ret)
>  		return ret;
>  
> -	/* Mask invalid MXCSR bits (for historical reasons). */
> -	newstate.mxcsr &= mxcsr_feature_mask;
> +	/* Do not allow an invalid MXCSR value. */
> +	if (newstate.mxcsr & ~mxcsr_feature_mask)
> +		ret = -EINVAL;
>  
>  	fpu__prepare_write(fpu);

With that addressed:

Reviewed-by: Borislav Petkov <bp@...e.de>

Thx.

-- 
Regards/Gruss,
    Boris.

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