linux-kernel - Re: [PATCH v2 6/7] arm64: signal: nofpsimd: Handle fp/simd context for signal frames

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Date:   Fri, 10 Jan 2020 12:34:42 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        will@...nel.org, maz@...nel.org, mark.rutland@....com,
        dave.martin@....com, ard.biesheuvel@...aro.org,
        christoffer.dall@....com, Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v2 6/7] arm64: signal: nofpsimd: Handle fp/simd context
 for signal frames

On Tue, Dec 17, 2019 at 06:34:01PM +0000, Suzuki K Poulose wrote:
> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
> index dd2cdc0d5be2..c648f7627035 100644
> --- a/arch/arm64/kernel/signal.c
> +++ b/arch/arm64/kernel/signal.c
> @@ -173,6 +173,10 @@ static int preserve_fpsimd_context(struct fpsimd_context __user *ctx)
>  		&current->thread.uw.fpsimd_state;
>  	int err;
>  
> +	/* This must not be called when FP/SIMD support is missing */
> +	if (WARN_ON(!system_supports_fpsimd()))
> +		return -EINVAL;

I'd drop this, see below.

> @@ -191,6 +195,10 @@ static int restore_fpsimd_context(struct fpsimd_context __user *ctx)
>  	__u32 magic, size;
>  	int err = 0;
>  
> +	/* This must not be called when FP/SIMD support is missing */
> +	if (WARN_ON(!system_supports_fpsimd()))
> +		return -EINVAL;
> +
>  	/* check the magic/size information */
>  	__get_user_error(magic, &ctx->head.magic, err);
>  	__get_user_error(size, &ctx->head.size, err);
> @@ -261,6 +269,9 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user)
>  	struct user_fpsimd_state fpsimd;
>  	struct sve_context sve;
>  
> +	if (WARN_ON(!system_supports_fpsimd()))
> +		return -EINVAL;
> +
>  	if (__copy_from_user(&sve, user->sve, sizeof(sve)))
>  		return -EFAULT;
>  
> @@ -371,6 +382,8 @@ static int parse_user_sigframe(struct user_ctxs *user,
>  			goto done;
>  
>  		case FPSIMD_MAGIC:
> +			if (!system_supports_fpsimd())
> +				goto invalid;
>  			if (user->fpsimd)
>  				goto invalid;
>  
> @@ -506,7 +519,7 @@ static int restore_sigframe(struct pt_regs *regs,
>  	if (err == 0)
>  		err = parse_user_sigframe(&user, sf);
>  
> -	if (err == 0) {
> +	if (err == 0 && system_supports_fpsimd()) {
>  		if (!user.fpsimd)
>  			return -EINVAL;

I don't think we need to be over paranoid here and add three/four checks
and two warnings in static functions. parse_user_sigframe() already
returns -EINVAL if SVE or FPSIMD is missing (the latter with your check
above). We don't need this additional check in restore_sigframe() and
restore_{sve_,}fpsimd_context(), the call paths are simple enough.

>  
> @@ -623,7 +636,7 @@ static int setup_sigframe(struct rt_sigframe_user_layout *user,
>  
>  	err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(*set));
>  
> -	if (err == 0) {
> +	if (err == 0 && system_supports_fpsimd()) {
>  		struct fpsimd_context __user *fpsimd_ctx =
>  			apply_user_offset(user, user->fpsimd_offset);
>  		err |= preserve_fpsimd_context(fpsimd_ctx);

This check is also sufficient for a static function not to have the
WARN_ON.

> diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
> index 12a585386c2f..97ace6919bc2 100644
> --- a/arch/arm64/kernel/signal32.c
> +++ b/arch/arm64/kernel/signal32.c
> @@ -100,6 +100,9 @@ static int compat_preserve_vfp_context(struct compat_vfp_sigframe __user *frame)
>  	compat_ulong_t fpscr, fpexc;
>  	int i, err = 0;
>  
> +	/* This must not be called when the FP/SIMD is missing */
> +	if (WARN_ON(!system_supports_fpsimd()))
> +		return -EINVAL;
>  	/*
>  	 * Save the hardware registers to the fpsimd_state structure.
>  	 * Note that this also saves V16-31, which aren't visible
> @@ -149,6 +152,10 @@ static int compat_restore_vfp_context(struct compat_vfp_sigframe __user *frame)
>  	compat_ulong_t fpscr;
>  	int i, err = 0;
>  
> +	/* This must not be called when the FP/SIMD is missing */
> +	if (WARN_ON(!system_supports_fpsimd()))
> +		return -EINVAL;
> +
>  	__get_user_error(magic, &frame->magic, err);
>  	__get_user_error(size, &frame->size, err);
>  
> @@ -223,7 +230,7 @@ static int compat_restore_sigframe(struct pt_regs *regs,
>  	err |= !valid_user_regs(&regs->user_regs, current);
>  
>  	aux = (struct compat_aux_sigframe __user *) sf->uc.uc_regspace;
> -	if (err == 0)
> +	if (err == 0 && system_supports_fpsimd())
>  		err |= compat_restore_vfp_context(&aux->vfp);
>  
>  	return err;
> @@ -419,7 +426,7 @@ static int compat_setup_sigframe(struct compat_sigframe __user *sf,
>  
>  	aux = (struct compat_aux_sigframe __user *) sf->uc.uc_regspace;
>  
> -	if (err == 0)
> +	if (err == 0 && system_supports_fpsimd())
>  		err |= compat_preserve_vfp_context(&aux->vfp);
>  	__put_user_error(0, &aux->end_magic, err);

Same comments as for the native signals.

-- 
Catalin