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Howlett" , Vlastimil Babka , Jann Horn , Eric Biederman , Alexander Viro , Christian Brauner , Jan Kara , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/5] mm: abstract get_arg_page() stack expansion and mmap read lock Message-ID: <202412131701.81693C36C@keescook> References: <5295d1c70c58e6aa63d14be68d4e1de9fa1c8e6d.1733248985.git.lorenzo.stoakes@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5295d1c70c58e6aa63d14be68d4e1de9fa1c8e6d.1733248985.git.lorenzo.stoakes@oracle.com> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 05881160009 X-Stat-Signature: dyhy686e7ebei7j4i84da7fn1j7rjgjt X-Rspam-User: X-HE-Tag: 1734138311-504083 X-HE-Meta: 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 aW5+gSQy OummRxw/5yI7AFFaP3vgUqX9lgecC8E14i9DNrxpeC5vfKbAywHEJkh8B6SPpNmyvilrCyF7RyBh99ivZWN63qGJGqwoE2HTV7MmSA44Uu54A31rxZQ9nETdcRglQkU7QRljXruvnbqhk5HPP8d5lxlPhsyLA1sdym5pJi8jaRhdhxSin3SA0XGkUH1MOUhq9p3+RaHcuzK5mambUBfL7JfJ7E1hQKdNSQD7owsayX0jgBzsm7GJI28LyfShq4y1oETYa3D5A1dWgi4JrogGkXPdCsqz3PNjMJ0W0mAJCvZGbDgl7gVeYNHktDOCNDULSj4YV 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: List-Subscribe: List-Unsubscribe: On Tue, Dec 03, 2024 at 06:05:10PM +0000, Lorenzo Stoakes wrote: > Right now fs/exec.c invokes expand_downwards(), an otherwise internal > implementation detail of the VMA logic in order to ensure that an arg page > can be obtained by get_user_pages_remote(). I think this is already in -next, but yeah, this looks good. It does mix some logic changes, but it's pretty minor. > - if (write && pos < vma->vm_start) { > - mmap_write_lock(mm); > - ret = expand_downwards(vma, pos); > - if (unlikely(ret < 0)) { > - mmap_write_unlock(mm); > - return NULL; > - } > - mmap_write_downgrade(mm); > - } else > - mmap_read_lock(mm); > + if (!mmap_read_lock_maybe_expand(mm, vma, pos, write)) > + return NULL; > > [...] > + if (!write || addr >= new_vma->vm_start) { > + mmap_read_lock(mm); > + return true; > + } > + > + if (!(new_vma->vm_flags & VM_GROWSDOWN)) > + return false; The VM_GROWSDOWN check is moved around a bit. It seems okay, though. > + > + mmap_write_lock(mm); > + if (expand_downwards(new_vma, addr)) { > + mmap_write_unlock(mm); > + return false; > + } > + > + mmap_write_downgrade(mm); > + return true; I actually find this much more readable now since it follows the more common "bail out early" coding style. Acked-by: Kees Cook Thanks! -Kees -- Kees Cook