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Message-ID: <6cb7df56-0479-30be-5389-b4b819572deb@intel.com>
Date:   Tue, 16 May 2023 16:14:47 -0700
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Subject: Re: [PATCH 1/6] PKEY: Introduce PKEY_ENFORCE_API flag
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To:     jeffxu@chromium.org, luto@kernel.org, jorgelo@chromium.org,
        keescook@chromium.org, groeck@chromium.org, jannh@google.com,
        sroettger@google.com
Cc:     akpm@linux-foundation.org, jeffxu@google.com,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-mm@kvack.org, linux-hardening@vger.kernel.org
References: <20230515130553.2311248-1-jeffxu@chromium.org>
 <20230515130553.2311248-2-jeffxu@chromium.org>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <20230515130553.2311248-2-jeffxu@chromium.org>
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On 5/15/23 06:05, jeffxu@chromium.org wrote:
> --- a/arch/x86/mm/pkeys.c
> +++ b/arch/x86/mm/pkeys.c
> @@ -20,7 +20,7 @@ int __execute_only_pkey(struct mm_struct *mm)
>  	/* Do we need to assign a pkey for mm's execute-only maps? */
>  	if (execute_only_pkey == -1) {
>  		/* Go allocate one to use, which might fail */
> -		execute_only_pkey = mm_pkey_alloc(mm);
> +		execute_only_pkey = mm_pkey_alloc(mm, 0);
>  		if (execute_only_pkey < 0)
>  			return -1;
>  		need_to_set_mm_pkey = true;

In your threat model, what mechanism prevents the attacker from
modifying executable mappings?

I was trying to figure out if the implicit execute-only pkey should have
the PKEY_ENFORCE_API bit set.  I think that in particular would probably
cause some kind of ABI breakage, but it still reminded me that I have an
incomplete picture of the threat model.