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Fri, 29 May 2020 20:51:43 GMT Received: from b03ledav003.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B5AD36A04D; Fri, 29 May 2020 20:51:44 +0000 (GMT) Received: from b03ledav003.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D3E666A047; Fri, 29 May 2020 20:51:43 +0000 (GMT) Received: from Buonos-Thinkpad-X1.ibm.com (unknown [9.65.226.57]) by b03ledav003.gho.boulder.ibm.com (Postfix) with ESMTP; Fri, 29 May 2020 20:51:43 +0000 (GMT) From: Daniele Buono To: qemu-devel@nongnu.org Subject: [PATCH v2 1/4] coroutine: support SafeStack in ucontext backend Date: Fri, 29 May 2020 16:51:19 -0400 Message-Id: <20200529205122.714-2-dbuono@linux.vnet.ibm.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200529205122.714-1-dbuono@linux.vnet.ibm.com> References: <20200529205122.714-1-dbuono@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216, 18.0.687 definitions=2020-05-29_10:2020-05-28, 2020-05-29 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 spamscore=0 cotscore=-2147483648 phishscore=0 impostorscore=0 malwarescore=0 priorityscore=1501 lowpriorityscore=0 suspectscore=3 adultscore=0 mlxscore=0 clxscore=1015 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005290148 Received-SPF: none client-ip=148.163.158.5; envelope-from=dbuono@linux.vnet.ibm.com; helo=mx0a-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/29 15:28:52 X-ACL-Warn: Detected OS = Linux 3.x [generic] X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, KHOP_DYNAMIC=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-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 , =?UTF-8?q?Daniel=20P=20=2E=20Berrang=C3=A9?= , Stefan Hajnoczi , Paolo Bonzini , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , dbuono@linux.vnet.ibm.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" LLVM's SafeStack instrumentation does not yet support programs that make use of the APIs in ucontext.h With the current implementation of coroutine-ucontext, the resulting binary is incorrect, with different coroutines sharing the same unsafe stack and producing undefined behavior at runtime. This fix allocates an additional unsafe stack area for each coroutine, and sets the new unsafe stack pointer before calling swapcontext() in qemu_coroutine_new. This is the only place where the pointer needs to be manually updated, since sigsetjmp/siglongjmp are already instrumented by LLVM to properly support SafeStack. The additional stack is then freed in qemu_coroutine_delete. Signed-off-by: Daniele Buono --- include/qemu/coroutine_int.h | 5 +++++ util/coroutine-ucontext.c | 26 ++++++++++++++++++++++++++ 2 files changed, 31 insertions(+) diff --git a/include/qemu/coroutine_int.h b/include/qemu/coroutine_int.h index bd6b0468e1..1da148552f 100644 --- a/include/qemu/coroutine_int.h +++ b/include/qemu/coroutine_int.h @@ -28,6 +28,11 @@ #include "qemu/queue.h" #include "qemu/coroutine.h" +#ifdef CONFIG_SAFESTACK +/* Pointer to the unsafe stack, defined by the compiler */ +extern __thread void *__safestack_unsafe_stack_ptr; +#endif + #define COROUTINE_STACK_SIZE (1 << 20) typedef enum { diff --git a/util/coroutine-ucontext.c b/util/coroutine-ucontext.c index bd593e61bc..9108eb1294 100644 --- a/util/coroutine-ucontext.c +++ b/util/coroutine-ucontext.c @@ -41,6 +41,11 @@ typedef struct { Coroutine base; void *stack; size_t stack_size; +#ifdef CONFIG_SAFESTACK + /* Need an unsafe stack for each coroutine */ + void *unsafe_stack; + size_t unsafe_stack_size; +#endif sigjmp_buf env; #ifdef CONFIG_VALGRIND_H @@ -140,6 +145,10 @@ Coroutine *qemu_coroutine_new(void) co = g_malloc0(sizeof(*co)); co->stack_size = COROUTINE_STACK_SIZE; co->stack = qemu_alloc_stack(&co->stack_size); +#ifdef CONFIG_SAFESTACK + co->unsafe_stack_size = COROUTINE_STACK_SIZE; + co->unsafe_stack = qemu_alloc_stack(&co->unsafe_stack_size); +#endif co->base.entry_arg = &old_env; /* stash away our jmp_buf */ uc.uc_link = &old_uc; @@ -160,6 +169,20 @@ Coroutine *qemu_coroutine_new(void) /* swapcontext() in, siglongjmp() back out */ if (!sigsetjmp(old_env, 0)) { start_switch_fiber(&fake_stack_save, co->stack, co->stack_size); +#ifdef CONFIG_SAFESTACK + /* + * Before we swap the context, set the new unsafe stack + * The unsafe stack grows just like the normal stack, so start from + * the last usable location of the memory area. + * NOTE: we don't have to re-set the usp afterwards because we are + * coming back to this context through a siglongjmp. + * The compiler already wrapped the corresponding sigsetjmp call with + * code that saves the usp on the (safe) stack before the call, and + * restores it right after (which is where we return with siglongjmp). + */ + void *usp = co->unsafe_stack + co->unsafe_stack_size; + __safestack_unsafe_stack_ptr = usp; +#endif swapcontext(&old_uc, &uc); } @@ -192,6 +215,9 @@ void qemu_coroutine_delete(Coroutine *co_) #endif qemu_free_stack(co->stack, co->stack_size); +#ifdef CONFIG_SAFESTACK + qemu_free_stack(co->unsafe_stack, co->unsafe_stack_size); +#endif g_free(co); } -- 2.26.2