linux-kernel - Re: [PATCH 29/29] x86/fpu: Defer FPU state load until return to userspace

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Message-ID: <20181129150016.bqjgc5t5qcafdplz@linutronix.de>
Date:   Thu, 29 Nov 2018 16:00:16 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...riel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 29/29] x86/fpu: Defer FPU state load until return to
 userspace

On 2018-11-28 23:20:35 [+0100], To linux-kernel@...r.kernel.org wrote:
> diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
> index fb16d0da71bca..f552b1d6c6958 100644
> --- a/arch/x86/kernel/fpu/signal.c
> +++ b/arch/x86/kernel/fpu/signal.c
> @@ -292,43 +295,51 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
>  		u64 init_bv = xfeatures_mask & ~xfeatures;
>  
>  		if (using_compacted_format()) {
> -			ret = copy_user_to_xstate(&state->xsave, buf_fx);
> +			ret = copy_user_to_xstate(&fpu->state.xsave, buf_fx);
>  		} else {
> -			ret = __copy_from_user(&state->xsave, buf_fx, state_size);
> +			ret = __copy_from_user(&fpu->state.xsave, buf_fx, state_size);
>  
>  			if (!ret && state_size > offsetof(struct xregs_state, header))
> -				ret = validate_xstate_header(&state->xsave.header);
> +				ret = validate_xstate_header(&fpu->state.xsave.header);
>  		}
>  		if (ret)
>  			goto err_out;
>  
> -		sanitize_restored_xstate(state, envp, xfeatures, fx_only);
> +		sanitize_restored_xstate(&fpu->state, envp, xfeatures, fx_only);
>  
> +		__fpregs_changes_begin();
>  		if (unlikely(init_bv))
>  			copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
> -		ret = copy_users_to_xregs(&state->xsave, xfeatures);
> +		ret = copy_users_to_xregs(&fpu->state.xsave, xfeatures);
>  
>  	} else if (use_fxsr()) {
> -		ret = __copy_from_user(&state->fxsave, buf_fx, state_size);
> -		if (ret)
> +		ret = __copy_from_user(&fpu->state.fxsave, buf_fx, state_size);
> +		if (ret) {
> +			err = -EFAULT;
>  			goto err_out;
> +		}
>  
> -		sanitize_restored_xstate(state, envp, xfeatures, fx_only);
> +		sanitize_restored_xstate(&fpu->state, &env, xfeatures, fx_only);

This should have remained `envp' and not become `&env'.

Sebastian