linux-kernel - Re: [PATCH 5/8] x86, pkeys: allocation/free syscalls

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Message-ID: <20160601123705.72a606e7@lwn.net>
Date:	Wed, 1 Jun 2016 12:37:05 -0600
From:	Jonathan Corbet <corbet@....net>
To:	Dave Hansen <dave@...1.net>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-mm@...ck.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, dave.hansen@...ux.intel.com
Subject: Re: [PATCH 5/8] x86, pkeys: allocation/free syscalls

Sorry, I have one more obnoxious question...

> +static inline
> +int mm_pkey_free(struct mm_struct *mm, int pkey)
> +{
> +	/*
> +	 * pkey 0 is special, always allocated and can never
> +	 * be freed.
> +	 */
> +	if (!pkey || !validate_pkey(pkey))
> +		return -EINVAL;
> +	if (!mm_pkey_is_allocated(mm, pkey))
> +		return -EINVAL;
> +
> +	mm_set_pkey_free(mm, pkey);
> +
> +	return 0;
> +}

If I read this right, it doesn't actually remove any pkey restrictions
that may have been applied while the key was allocated.  So there could be
pages with that key assigned that might do surprising things if the key is
reallocated for another use later, right?  Is that how the API is intended
to work?

Thanks,

jon