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Date:   Fri, 1 Dec 2023 13:47:28 +0000
From:   Mark Brown <broonie@kernel.org>
To:     Szabolcs Nagy <Szabolcs.Nagy@arm.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        "Rick P. Edgecombe" <rick.p.edgecombe@intel.com>,
        Deepak Gupta <debug@rivosinc.com>,
        "H.J. Lu" <hjl.tools@gmail.com>,
        Florian Weimer <fweimer@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Christian Brauner <brauner@kernel.org>,
        Shuah Khan <shuah@kernel.org>, linux-kernel@vger.kernel.org,
        Will Deacon <will@kernel.org>,
        Kees Cook <keescook@chromium.org>, jannh@google.com,
        linux-kselftest@vger.kernel.org, linux-api@vger.kernel.org,
        David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH RFT v4 0/5] fork: Support shadow stacks in clone3()
Message-ID: <dd1c8cc6-2f37-4348-b2b8-12ab0e8eca7a@sirena.org.uk>
References: <20231128-clone3-shadow-stack-v4-0-8b28ffe4f676@kernel.org>
 <ZWjb6r0RWPo199pC@arm.com>
 <fce4c169-5d19-40e8-bc32-0abec9bb008e@sirena.org.uk>
 <ZWnIgQgUW0Eyfcw9@arm.com>
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On Fri, Dec 01, 2023 at 11:50:25AM +0000, Szabolcs Nagy wrote:
> The 11/30/2023 21:51, Mark Brown wrote:
> > The concern Rick raised was that allowing user to pick the exact shadow
> > stack pointer would allow userspace to corrupt or reuse the stack of an
> > existing thread by starting a new thread with the shadow stack pointing
> > into the existing shadow stack of that thread.  While in isolation

> note that this can be prevented by map_shadow_stack adding
> a token that clone3 verifies.

That would make it impossible to reuse the shadow stack once the token
is overwritten which does move the needle more towards making doing the
mapping separately pure overhead.

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