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[216.160.65.90]) by smtp.gmail.com with ESMTPSA id o26sm7440028pfp.219.2020.07.24.14.23.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 Jul 2020 14:23:15 -0700 (PDT) From: Richard Henderson To: qemu-devel@nongnu.org Subject: [PATCH] linux-user: Ensure mmap_min_addr is non-zero Date: Fri, 24 Jul 2020 14:23:14 -0700 Message-Id: <20200724212314.545877-1-richard.henderson@linaro.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::1042; envelope-from=richard.henderson@linaro.org; helo=mail-pj1-x1042.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: alex.bennee@linaro.org, laurent@vivier.eu, John Paul Adrian Glaubitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" When the chroot does not have /proc mounted, we can read neither /proc/sys/vm/mmap_min_addr nor /proc/sys/maps. The enforcement of mmap_min_addr in the host kernel is done by the security module, and so does not apply to processes owned by root. Which leads pgd_find_hole_fallback to succeed in probing a reservation at address 0. Which confuses pgb_reserved_va to believe that guest_base has not actually been initialized. We don't actually want NULL addresses to become accessible, so make sure that mmap_min_addr is initialized with a non-zero value. Buglink: https://bugs.launchpad.net/qemu/+bug/1888728 Reported-by: John Paul Adrian Glaubitz Signed-off-by: Richard Henderson --- linux-user/main.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/linux-user/main.c b/linux-user/main.c index 3597e99bb1..75c9785157 100644 --- a/linux-user/main.c +++ b/linux-user/main.c @@ -758,14 +758,26 @@ int main(int argc, char **argv, char **envp) if ((fp = fopen("/proc/sys/vm/mmap_min_addr", "r")) != NULL) { unsigned long tmp; - if (fscanf(fp, "%lu", &tmp) == 1) { + if (fscanf(fp, "%lu", &tmp) == 1 && tmp != 0) { mmap_min_addr = tmp; - qemu_log_mask(CPU_LOG_PAGE, "host mmap_min_addr=0x%lx\n", mmap_min_addr); + qemu_log_mask(CPU_LOG_PAGE, "host mmap_min_addr=0x%lx\n", + mmap_min_addr); } fclose(fp); } } + /* + * We prefer to not make NULL pointers accessible to QEMU. + * If we're in a chroot with no /proc, fall back to 1 page. + */ + if (mmap_min_addr == 0) { + mmap_min_addr = qemu_host_page_size; + qemu_log_mask(CPU_LOG_PAGE, + "host mmap_min_addr=0x%lx (fallback)\n", + mmap_min_addr); + } + /* * Prepare copy of argv vector for target. */ -- 2.25.1