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([2607:fb91:1ee6:5be8:2af4:40ea:5991:dc59]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-23fa475fc12sm19378545ad.5.2025.07.24.09.33.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 24 Jul 2025 09:33:55 -0700 (PDT) Message-ID: Date: Thu, 24 Jul 2025 09:33:52 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] system/physmem: fix use-after-free with dispatch To: Pierrick Bouvier , qemu-devel@nongnu.org Cc: =?UTF-8?Q?Alex_Benn=C3=A9e?= , Gustavo Romero , Michael Tokarev , =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= , Peter Maydell , David Hildenbrand , Manos Pitsidianakis , Paolo Bonzini , Mark Cave-Ayland , Peter Xu , Mark Cave-Ayland References: <20250724161142.2803091-1-pierrick.bouvier@linaro.org> Content-Language: en-US From: Richard Henderson In-Reply-To: <20250724161142.2803091-1-pierrick.bouvier@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::52d; envelope-from=richard.henderson@linaro.org; helo=mail-pg1-x52d.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 7/24/25 09:11, Pierrick Bouvier wrote: > This patch takes a simple approach: remove the cached value creating the > issue, and make sure we always get the current mapping for address > space, using address_space_to_dispatch(cpu->cpu_ases[asidx].as). > It's equivalent to qatomic_rcu_read(&as->current_map)->dispatch; > This is not really costly, we just need two dereferences, > including one atomic (rcu) read, which is negligible considering we are > already on mmu slow path anyway. We're not just on the slow path, we're on the tlb fill path, which is even rarer. Once upon a time, memory_dispatch was used along the mmio path, but even then I think it must have been premature optimization. This looks like an excellent solution. Thanks for all the detective work. Reviewed-by: Richard Henderson r~