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[88.21.207.26]) by smtp.gmail.com with ESMTPSA id v7sm394316wmg.3.2020.05.04.07.55.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 May 2020 07:55:49 -0700 (PDT) Subject: Re: [PATCH 0/4] Add support for SafeStack To: Daniele Buono , qemu-devel@nongnu.org References: <20200429194420.21147-1-dbuono@linux.vnet.ibm.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Mon, 4 May 2020 16:55:48 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200429194420.21147-1-dbuono@linux.vnet.ibm.com> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=WINDOWS-1252; format=flowed Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=205.139.110.120; envelope-from=philmd@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/04 04:24:57 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] 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, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN 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: Kevin Wolf , Paolo Bonzini , Tobin Feldman-Fitzthum , Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/29/20 9:44 PM, Daniele Buono wrote: > LLVM supports SafeStack instrumentation to protect against stack buffer > overflows, since version 3.7 >=20 > From https://clang.llvm.org/docs/SafeStack.html: > "It works by separating the program stack into two distinct regions: the > safe stack and the unsafe stack. The safe stack stores return addresses, > register spills, and local variables that are always accessed in a safe > way, while the unsafe stack stores everything else. This separation > ensures that buffer overflows on the unsafe stack cannot be used to > overwrite anything on the safe stack." >=20 > Unfortunately, the use of two stack regions does not cope well with > QEMU's coroutines. The second stack region is not properly set up with > both ucontext and sigaltstack, so multiple coroutines end up sharing the > same memory area for the unsafe stack, causing undefined behaviors at > runtime (and most iochecks to fail). >=20 > This patch series fixes the implementation of the ucontext backend and > make sure that sigaltstack is never used if the compiler is applying > the SafeStack instrumentation. It also adds a configure flag to enable > SafeStack, and enables iotests when SafeStack is used. >=20 > This is an RFC mainly because of the low-level use of the SafeStack > runtime. > When running swapcontext(), we have to manually set the unsafe stack > pointer to the new area allocated for the coroutine. LLVM does not allow > this by using builtin, so we have to use implementation details that may > change in the future. > This patch has been tested briefly ( make check on an x86 system ) with > clang v3.9, v4.0, v5.0, v6.0 > Heavier testing, with make check-acceptance has been performed with > clang v7.0 Clang10: Tested-by: Philippe Mathieu-Daud=E9 >=20 > Daniele Buono (4): > coroutine: support SafeStack in ucontext backend > coroutine: Add check for SafeStack in sigalstack > configure: add flag to enable SafeStack > check-block: Enable iotests with SafeStack >=20 > configure | 29 +++++++++++++++++++++++++++++ > include/qemu/coroutine_int.h | 6 ++++++ > tests/check-block.sh | 12 +++++++++++- > util/coroutine-sigaltstack.c | 4 ++++ > util/coroutine-ucontext.c | 25 +++++++++++++++++++++++++ > 5 files changed, 75 insertions(+), 1 deletion(-) >=20