From patchwork Tue Jun 14 11:49:18 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Maydell X-Patchwork-Id: 9175651 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id CED566075D for ; Tue, 14 Jun 2016 11:49:54 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id BF7A920223 for ; Tue, 14 Jun 2016 11:49:54 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B444826490; Tue, 14 Jun 2016 11:49:54 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 23A6B25EF7 for ; Tue, 14 Jun 2016 11:49:52 +0000 (UTC) Received: from localhost ([::1]:34392 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bCmqq-0005Xq-Bp for patchwork-qemu-devel@patchwork.kernel.org; Tue, 14 Jun 2016 07:49:48 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56108) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bCmqX-0005XH-8q for qemu-devel@nongnu.org; Tue, 14 Jun 2016 07:49:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bCmqR-0005G7-Pk for qemu-devel@nongnu.org; Tue, 14 Jun 2016 07:49:27 -0400 Received: from orth.archaic.org.uk ([2001:8b0:1d0::2]:57702) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bCmqR-0005Fl-HA for qemu-devel@nongnu.org; Tue, 14 Jun 2016 07:49:23 -0400 Received: from pm215 by orth.archaic.org.uk with local (Exim 4.84_2) (envelope-from ) id 1bCmqN-0006A3-Ho; Tue, 14 Jun 2016 12:49:19 +0100 From: Peter Maydell To: qemu-devel@nongnu.org Date: Tue, 14 Jun 2016 12:49:18 +0100 Message-Id: <1465904958-27233-1-git-send-email-peter.maydell@linaro.org> X-Mailer: git-send-email 1.9.1 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2001:8b0:1d0::2 Subject: [Qemu-devel] [PATCH] linux-user: Don't use sigfillset() on uc->uc_sigmask X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Riku Voipio , Richard Henderson , Laurent Vivier , patches@linaro.org Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP The kernel and libc have different ideas about what a sigset_t is -- for the kernel it is only _NSIG / 8 bytes in size (usually 8 bytes), but for libc it is much larger, 128 bytes. In most situations the difference doesn't matter, because if you pass a pointer to a libc sigset_t to the kernel it just acts on the first 8 bytes of it, but for the ucontext_t* argument to a signal handler it trips us up. The kernel allocates this ucontext_t on the stack according to its idea of the sigset_t type, but the type of the ucontext_t defined by the libc headers uses the libc type, and so do the manipulator functions like sigfillset(). This means that (1) sizeof(uc->uc_sigmask) is much larger than the actual space used on the stack (2) sigfillset(&uc->uc_sigmask) will write garbage 0xff bytes off the end of the structure, which can trash data that was on the stack before the signal handler was invoked, and may result in a crash after the handler returns To avoid this, we use a memset() of the correct size to fill the signal mask rather than using the libc function. This fixes a problem where we would crash at least some of the time on an i386 host when a signal was taken. Signed-off-by: Peter Maydell Reviewed-by: Laurent Vivier --- linux-user/qemu.h | 5 +++++ linux-user/signal.c | 10 +++++++++- linux-user/syscall.c | 5 ----- 3 files changed, 14 insertions(+), 6 deletions(-) diff --git a/linux-user/qemu.h b/linux-user/qemu.h index 56f29c3..e8a5aed 100644 --- a/linux-user/qemu.h +++ b/linux-user/qemu.h @@ -20,6 +20,11 @@ #define THREAD __thread +/* This is the size of the host kernel's sigset_t, needed where we make + * direct system calls that take a sigset_t pointer and a size. + */ +#define SIGSET_T_SIZE (_NSIG / 8) + /* This struct is used to hold certain information about the image. * Basically, it replicates in user space what would be certain * task_struct fields in the kernel diff --git a/linux-user/signal.c b/linux-user/signal.c index 37fb60f..26e5e94 100644 --- a/linux-user/signal.c +++ b/linux-user/signal.c @@ -639,8 +639,16 @@ static void host_signal_handler(int host_signum, siginfo_t *info, * code in case the guest code provokes one in the window between * now and it getting out to the main loop. Signals will be * unblocked again in process_pending_signals(). + * + * WARNING: we cannot use sigfillset() here because the uc_sigmask + * field is a kernel sigset_t, which is much smaller than the + * libc sigset_t which sigfillset() operates on. Using sigfillset() + * would write 0xff bytes off the end of the structure and trash + * data on the struct. + * We can't use sizeof(uc->uc_sigmask) either, because the libc + * headers define the struct field with the wrong (too large) type. */ - sigfillset(&uc->uc_sigmask); + memset(&uc->uc_sigmask, 0xff, SIGSET_T_SIZE); sigdelset(&uc->uc_sigmask, SIGSEGV); sigdelset(&uc->uc_sigmask, SIGBUS); diff --git a/linux-user/syscall.c b/linux-user/syscall.c index 121b89f..202e387 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -124,11 +124,6 @@ int __clone2(int (*fn)(void *), void *child_stack_base, #define VFAT_IOCTL_READDIR_BOTH _IOR('r', 1, struct linux_dirent [2]) #define VFAT_IOCTL_READDIR_SHORT _IOR('r', 2, struct linux_dirent [2]) -/* This is the size of the host kernel's sigset_t, needed where we make - * direct system calls that take a sigset_t pointer and a size. - */ -#define SIGSET_T_SIZE (_NSIG / 8) - #undef _syscall0 #undef _syscall1 #undef _syscall2