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spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:52958 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k09Lp-0007kD-Dh for qemu-devel@archiver.kernel.org; Mon, 27 Jul 2020 16:03:57 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:52408) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k09LF-0007K1-R9 for qemu-devel@nongnu.org; Mon, 27 Jul 2020 16:03:21 -0400 Received: from mout.kundenserver.de ([217.72.192.73]:40107) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k09LD-0006HQ-UT for qemu-devel@nongnu.org; Mon, 27 Jul 2020 16:03:21 -0400 Received: from [192.168.100.1] ([82.252.135.186]) by mrelayeu.kundenserver.de (mreue109 [213.165.67.119]) with ESMTPSA (Nemesis) id 1MBDvU-1k54lZ2vcc-00CeqS; Mon, 27 Jul 2020 22:03:15 +0200 Subject: Re: [PATCH] linux-user: Ensure mmap_min_addr is non-zero To: Richard Henderson , qemu-devel@nongnu.org References: <20200724212314.545877-1-richard.henderson@linaro.org> From: Laurent Vivier Autocrypt: addr=laurent@vivier.eu; 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envelope-from=laurent@vivier.eu; helo=mout.kundenserver.de X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/27 16:03:18 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_NONE=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, John Paul Adrian Glaubitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Le 24/07/2020 à 23:23, Richard Henderson a écrit : > 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. > */ > Applied to my linux-user-for-5.1 branch. Thanks, Laurent