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

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Date:   Wed, 22 Jan 2020 11:09:47 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Cyrill Gorcunov <gorcunov@...il.com>,
        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
Subject: Re: [PATCH] x86/pkeys: add check for pkey "overflow"

On 1/22/20 10:51 AM, Cyrill Gorcunov wrote:
>> +	/*
>> +	 * 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;
> 	}

I don't feel strongly about it.  The reason I didn't do that is to
minimize the chance that this would cause any functional regression.

It's not a huge chance, but I've certainly fat-fingered my share of
off-by-one bugs.