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Tue, 16 May 2023 16:56:05 -0700 (PDT) MIME-Version: 1.0 References: <20230515130553.2311248-1-jeffxu@chromium.org> <20230515130553.2311248-2-jeffxu@chromium.org> <6cb7df56-0479-30be-5389-b4b819572deb@intel.com> In-Reply-To: <6cb7df56-0479-30be-5389-b4b819572deb@intel.com> From: Jeff Xu Date: Tue, 16 May 2023 16:55:28 -0700 Message-ID: Subject: Re: [PATCH 1/6] PKEY: Introduce PKEY_ENFORCE_API flag To: Dave Hansen Cc: jeffxu@chromium.org, luto@kernel.org, jorgelo@chromium.org, keescook@chromium.org, groeck@chromium.org, jannh@google.com, sroettger@google.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-hardening@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: eftwhhdqrzefmputmg5nrr8aboystfyo X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 02844C0009 X-HE-Tag: 1684281367-328063 X-HE-Meta: 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 sDr7ptWQ DlbdBJHVDNA53lZk18/9aEhOM0d+lVa2trJ7Ep8JxLiNS7ABqMN0hgFG9sW3nMkJ0kuZp7+HkzF6hOG8gT56buC+p7JqL+OCttc9BQo3waD79dfCN1HytPHGQkIDct0+bhka4dZGPmHXNSIWE4Y6mJEgxU7JItTkOXmnQxshjcgnm3XV0GuUedhnoIutOICOINwSeSrKxvyq+Ac8pVJZLNK6K27E7gpQHL3BmGBS6Cgx86giu3ib4DPRDKy1pKcy7ZLkam60gohNl3EOMmmPUqO+a6W7pcuQy8V7pIg/6QD9+yBkC67WOlmPQSz597liWhFVhYzUJPgyEKwqJTbMAAqNI58QzGlHXwS7SsAabFyHwK58= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, May 16, 2023 at 4:14=E2=80=AFPM Dave Hansen = wrote: > > 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 =3D=3D -1) { > > /* Go allocate one to use, which might fail */ > > - execute_only_pkey =3D mm_pkey_alloc(mm); > > + execute_only_pkey =3D mm_pkey_alloc(mm, 0); > > if (execute_only_pkey < 0) > > return -1; > > need_to_set_mm_pkey =3D 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. Yes. The main reason for not adding it now is the ABI breakage. As a next step, we could potentially develop mseal(), which fits more to the code segment. The PKEY_ENFORCE_API allows munmap(), so the user case is slightly differen= t. I will leave the threat model / V8 specific question to Stephan.