linux-kernel - Re: [PATCH] x86/pkeys: add check for pkey "overflow"

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Date:   Wed, 22 Jan 2020 21:51:11 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, alex.shi@...ux.alibaba.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, bigeasy@...utronix.de,
        pankaj.laxminarayan.bharadiya@...el.com, aubrey.li@...ux.intel.com,
        dave.hansen@...el.com
Subject: Re: [PATCH] x86/pkeys: add check for pkey "overflow"

On Wed, Jan 22, 2020 at 08:53:46AM -0800, Dave Hansen wrote:
> 
> Alex Shi reported the pkey macros above arch_set_user_pkey_access()
> to be unused.  They are unused, and even refer to a nonexistent
> CONFIG option.
> 
> @@ -922,6 +920,13 @@ int arch_set_user_pkey_access(struct tas
>  	if (!boot_cpu_has(X86_FEATURE_OSPKE))
>  		return -EINVAL;
>  
> +	/*
> +	 * This code should only be called with valid 'pkey'
> +	 * values originating from in-kernel users.  Complain
> +	 * if a bad value is observed.
> +	 */
> +	WARN_ON_ONCE(pkey >= arch_max_pkey());

Should not we rather abort this operation and exit with EINVAL
or something similar instead of calling wrmsr with overflowed
value? IOW,

	if (pkey >= arch_max_pkey()) {
		WARN_ON_ONCE(1);
		return -EINVAL;
	}