linux-kernel - Re: [patch V3 59/66] x86/fpu/signal: Move initial checks into fpu__sig

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Message-ID: <YNIfdidWt/nRwIPa@zn.tnic>
Date:   Tue, 22 Jun 2021 19:35:50 +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 V3 59/66] x86/fpu/signal: Move initial checks into
 fpu__sig_restore()

On Fri, Jun 18, 2021 at 04:19:22PM +0200, Thomas Gleixner wrote:

> Subject: Re: [patch V3 59/66] x86/fpu/signal: Move initial checks into fpu__sig_restore()

fpu__restore_sig() is the name.

> __fpu_sig_restore() is convoluted and some of the basic checks can trivialy be done
> in the calling function as well as the final error handling of clearing user state.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/kernel/fpu/signal.c |   76 +++++++++++++++++++++++--------------------
>  1 file changed, 41 insertions(+), 35 deletions(-)

...

> @@ -490,15 +464,47 @@ static inline int xstate_sigframe_size(v
>   */
>  int fpu__restore_sig(void __user *buf, int ia32_frame)
>  {
> +	unsigned int size = xstate_sigframe_size();
>  	void __user *buf_fx = buf;
> -	int size = xstate_sigframe_size();
> +	bool ia32_fxstate = false;
> +	int ret;
>  
> +	if (unlikely(!buf)) {
> +		fpu__clear_user_states(&current->thread.fpu);

You could declare

	struct fpu *fpu = &tsk->thread.fpu;

above so that it is easier to read, as this call is done twice.

Also, you can do:

	int ret = 0;

	if (unlikely(!buf))
		goto out;

so that the exit paths converge at the end.

> +		return 0;
> +	}
> +
> +	ia32_frame &= (IS_ENABLED(CONFIG_X86_32) ||
> +		       IS_ENABLED(CONFIG_IA32_EMULATION));
> +
> +	/*
> +	 * Only FXSR enabled systems need the FX state quirk.
> +	 * FRSTOR does not need it and can use the fast path.
> +	 */
>  	if (ia32_frame && use_fxsr()) {
>  		buf_fx = buf + sizeof(struct fregs_state);
>  		size += sizeof(struct fregs_state);
> +		ia32_fxstate = true;
> +	}
> +
> +	if (!access_ok(buf, size)) {
> +		ret = -EACCES;
> +		goto out;
> +	}
> +
> +	if (!IS_ENABLED(CONFIG_X86_64) && !static_cpu_has(X86_FEATURE_FPU)) {

cpu_feature_enabled()

> +		return fpregs_soft_set(current, NULL, 0,
> +				       sizeof(struct user_i387_ia32_struct),
> +				       NULL, buf);

Err, don't you need to catch retval into ret here and goto out, like
before, so that you can call fpu__clear_user_states() on error?

-- 
Regards/Gruss,
    Boris.

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