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Howlett" Subject: Re: [PATCH v2] mm_access: simplify the security checks Message-ID: References: MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Mimecast-MFC-PROC-ID: JOqYNCn87LMWN77_b1d90NCpevXbmIShYFrUgIcQrVw_1780317755 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Stat-Signature: hey3hjraoxoxryuj6bug8mhn63hh4rgb X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 2DAAE40011 X-HE-Tag: 1780317762-722965 X-HE-Meta: U2FsdGVkX1+Ehmon1KypAFfTcHxTdyZIlRta512o8+Kti6Jh2Y5nNTsnzWpK09DKG7i5lbLFyGCcIkg5rat9rO5nz4/hbOxyDjkkSlczVAbCtjLyBclLGX7jRKJXQv8qtjfVANa5KB7KkFo+XzWUP6Gtj/YCXVvbhx0JQ2yMM4bLzJePVHwqeK7VC+eleAmY0ucTWbjVGEpvkVibDZhBIpDT6YZlH7ze/iUP5zgiix8vVK/IzvIFEiZr/UOfAhNFNti8+lMgd7gCdB+Vpr7V0EOfFNt2xSldIFfcheCvnoIpEk8tj5JCsu2nkWFpEKgHMP+VGgm2/v+cufByfT0C2xDHNmHqukDPJWNeJzJtmHjw5BBTKLjst8G57Qwc9UtbWe7R3esJhH0BEDiitYGhWjfXl/LFTefBAW1zSA7TFWcaUs+THU8lnqEwx7NVCYL3vmH5E9Sj7SLtoTjP8jjX0Kkd7NE315DckO6D6D/kYoTzgTiZw27K2JQrykmHe+D8+s/N3+AUpOLe8SS2zwEPC99O+yuHCRjRTVvgPSP5YS0x0Euud64+bEvYVsNOFHlmGWXSTMFuoU6wJmSHuhUx6qCwoRoqV1mS15fs3PZ9xe8mWCZ6DIQP27gR4nPF4uA+KraDlhph8Iq64rzQPfL6Zdpt+k2jIvdrFcpxly7CoJjhfciVWxCdRRCWg8M+qSN3cgq5GkwdxJv1rVyc+5dbgA/EeYPyFOZbMC95HzFgvC6JDfsGmvnwZJgpsWg8RXV2EM1uAt2klb6rK8uKzf/Ak58VaH+xXYEYNtCIKrF2C4V6USvlYpPXVmmpGuK633ctybDHNpc1MNXbZfEv0XGz6nXq9SI8osY9YURySsty/BIR4evsr90gKmd7wwMMhUdd7iEONAD3KeGWNXfiUu6JnLlJxROwvZ/Vur1IiJhCo50RW+bduHeXantBjwEChqlIICiR/G3TtasgF2Xj+3P LMtVzIyt 4iEMFXNddTUXa2MlhGjoroh5l2qSSK+lbkf6bY9xLOxP43tmupFaovwDg1ZZeQFK+SNRdkZbRh0wCdJsu2Gs06xPipNLALydrOhd/iHi2z3aFzDXBYZzGLoadQAcrh1e/24pYSWmO0xnib2PxHfBVv5mwmMBA3hNthQenGwuBqp6Yj7p1sZXjDzTNo+9L+AjEIgfeIUUQjF+oVJS9ZeAF3grQ90OExQ6Bc5RDh1teInQrUcEz8oL+MeWtbM+jAEihXQy+9mZusuMoZrGkHaGs5wUi7Qq2tZSEg9NfMJt2rd+7SSCdPj7lW8zruoeQVRptvW64WWRhH+TV+kkC0n4g160j/cL+ad1Vk8tBDGH19bWOHu9wfUEZiRd9tLOv6VbiMCZDFTwFywFJYLtmAaY6uzwMqQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 06/01, Lorenzo Stoakes wrote: > > +cc Liam for mm lifecycle stuff :) > > The subject here seems not quite right - you're adding complexity here in that > now there's a racey fast path. OK. See my reply to David. If it doesn't look like a simplification - lets forget this patch ;) > One behavioural change here though is that down_read_killable() was used > previously, so such a situation would return -EINTR, but now would instead > succeed. I don't really follow... SIGKILL from de_thread() or anything else can come right after down_read_killable(). > > All we need for correctness is READ_ONCE() to ensure the compiler > > won't reload task->mm. This is not enough for KCSAN, but we already > > I'm not sure 'this is not enough for KCSAN' is really reassuring :) If I understand correctly KCSAN will complain if (say) we race with the exiting task which does current->mm = NULL without WRITE_ONCE in exit_mm(). > It's useful to put a revision history (ideally with links to prior revisions) > below the --- line to explain how vN differs from v(N-1). Yes... I didn't do it this time because V2 doesn't differ from V1, I just removed the duplicated paragraph from the changelog. > Overall I'm not really convinced about this patch - this isn't simplifying > things, it's introducing subtle assumptions and I don't really see the > benefit? Thanks for review! lets forget this patch then. Oleg.