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([2a01:e0a:ed5:b1f0:90e8:1fdb:2cba:9db1]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42b53f1fd50sm37685360f8f.38.2025.11.19.03.21.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 19 Nov 2025 03:21:56 -0800 (PST) Message-ID: <18f5e9b1-d4f3-4c7c-90ce-aa9ca5032f40@linaro.org> Date: Wed, 19 Nov 2025 12:21:54 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/4] linux-user: fix reserved_va page leak in do_munmap To: Matthew Lugg , qemu-devel@nongnu.org Cc: laurent@vivier.eu, peter.maydell@linaro.org References: <20251117170954.31451-1-mlugg@mlugg.co.uk> <20251117170954.31451-4-mlugg@mlugg.co.uk> From: Richard Henderson Content-Language: en-US In-Reply-To: <20251117170954.31451-4-mlugg@mlugg.co.uk> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2a00:1450:4864:20::431; envelope-from=richard.henderson@linaro.org; helo=mail-wr1-x431.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 11/17/25 18:09, Matthew Lugg wrote: > The old logic had an off-by-one bug. For instance, assuming 4k pages on > host and guest, if 'len' is '4097' (indicating to unmap 2 pages), then > 'last = start + 4096', so 'real_last = start + 4095', so ultimately > 'real_len = 4096'. I do not believe this could cause any observable bugs > in guests, because `target_munmap` page-aligns the length it passes in. > However, calls to this function in `target_mremap` do not page-align the > length, so those calls could "drop" pages, leading to a part of the > reserved region becoming unmapped. At worst, a host allocation could get > mapped into that hole, then clobbered by a new guest mapping. > > Signed-off-by: Matthew Lugg > --- > linux-user/mmap.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) Reviewed-by: Richard Henderson r~