From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B3056C27C77 for ; Wed, 12 Jun 2024 13:48:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Hp5LFPHgnfrVTq7ygejxjdx9Ejal9WIM/AzR6eF8wRE=; b=h54TBJqAaA4JNGFFXCLj2t/uQ3 EVF937yjX801aESK1+GunstdAk3RJO6jc/HduMSy+MTg8AQb2FavuuYLlBZQDF3tZanul2Z/W93gi EIwHUJ66aBMuhSzJDFCWrZDKwLX+re4RCKqoMdu6V/2f/4VXeiNKTNPlxuPobIUB+2baeDyEsO48h sT2w01J0UeJugxk9gghrHmQRaBOdxvfaO7sxiDsiYFx+q/ADtdXXC5pzofv9Ih+H5x2Op9GpJZP3j lOiavoh/tkUFvQNW7YJfTdvI23DrdEP1d4rfXUAtJHaGa8qV4eOF98KPfYyxOu/xAaA0+aUcl9fhp BIGJuToQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sHOLB-0000000CnZS-0V4e; Wed, 12 Jun 2024 13:48:41 +0000 Received: from s3.sipsolutions.net ([2a01:4f8:242:246e::2] helo=sipsolutions.net) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1sHOL7-0000000CnW4-04xo for linux-um@lists.infradead.org; Wed, 12 Jun 2024 13:48:39 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sipsolutions.net; s=mail; h=Content-Transfer-Encoding:MIME-Version: References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Content-Type:Sender :Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From:Resent-To: Resent-Cc:Resent-Message-ID; bh=Hp5LFPHgnfrVTq7ygejxjdx9Ejal9WIM/AzR6eF8wRE=; t=1718200116; x=1719409716; b=miTadJFXl6BoWrrr62hzo+0UWxUZjwLvBNaNM/gXJh/wJkr Hc+dAdBGf5KQwXkn3w5HivAWl28JvWb748VCp5Yb120bKXI2EaquHm3AZc+05V1l9x47N5GImLdD8 95AEYq6v50i0tnho+8paUWJRlhDe+HCDfsnhX0MwEyBmuc2dVhJRZ3r41HD44RS+IsRNld8JqT25M y2iKKUorlyDOkJSncKJfMU63CI5/olJfUg32ppumXlRbTzV9DN+xV2piubUd8g6GG/HZJQMBLuBOS Iq8bJXcFx1mEgwqlwKPYwY13Fwrhr2liWSyFyES30X0ijANJyvpUrWqzCY50Zlwg==; Received: by sipsolutions.net with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.97) (envelope-from ) id 1sHOL4-0000000ALhN-3pL9; Wed, 12 Jun 2024 15:48:35 +0200 From: benjamin@sipsolutions.net To: linux-um@lists.infradead.org Cc: Benjamin Berg Subject: [PATCH v2 3/5] um: Do a double clone to disable rseq Date: Wed, 12 Jun 2024 15:48:02 +0200 Message-ID: <20240612134804.1626427-4-benjamin@sipsolutions.net> X-Mailer: git-send-email 2.45.1 In-Reply-To: <20240612134804.1626427-1-benjamin@sipsolutions.net> References: <20240612134804.1626427-1-benjamin@sipsolutions.net> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240612_064837_173726_A0592E93 X-CRM114-Status: GOOD ( 17.58 ) X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org From: Benjamin Berg Newer glibc versions are enabling rseq support by default. This remains enabled in the cloned child process, potentially causing the host kernel to write/read memory in the child. It appears that this was purely not an issue because the used memory area happened to be above TASK_SIZE and remains mapped. Note that a better approach would be to exec a small static binary that does not link with other libraries. Using a memfd and execveat the binary could be embedded into UML itself and it would result in an entirely clean execution environment for userspace. Signed-off-by: Benjamin Berg --- v2: Improved clone logic using CLONE_VFORK --- arch/um/os-Linux/skas/process.c | 55 ++++++++++++++++++++++++++++++--- 1 file changed, 50 insertions(+), 5 deletions(-) diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c index 41a288dcfc34..11bc6f4ce5b3 100644 --- a/arch/um/os-Linux/skas/process.c +++ b/arch/um/os-Linux/skas/process.c @@ -255,6 +255,32 @@ static int userspace_tramp(void *stack) int userspace_pid[NR_CPUS]; int kill_userspace_mm[NR_CPUS]; +struct tramp_data { + int pid; + void *clone_sp; + void *stack; +}; + +static int userspace_tramp_clone_vm(void *data) +{ + struct tramp_data *tramp_data = data; + + /* + * At this point we are still in the same VM as the parent, but rseq + * has been disabled for this process. + * Continue with the clone into the new userspace process, the kernel + * continues as soon as this process quits (CLONE_VFORK). + */ + + tramp_data->pid = clone(userspace_tramp, tramp_data->clone_sp, + CLONE_PARENT | CLONE_FILES | SIGCHLD, + tramp_data->stack); + if (tramp_data->pid < 0) + tramp_data->pid = -errno; + + exit(0); +} + /** * start_userspace() - prepare a new userspace process * @stub_stack: pointer to the stub stack. @@ -268,9 +294,10 @@ int kill_userspace_mm[NR_CPUS]; */ int start_userspace(unsigned long stub_stack) { + struct tramp_data tramp_data; void *stack; unsigned long sp; - int pid, status, n, flags, err; + int pid, status, n, err; /* setup a temporary stack page */ stack = mmap(NULL, UM_KERN_PAGE_SIZE, @@ -286,10 +313,13 @@ int start_userspace(unsigned long stub_stack) /* set stack pointer to the end of the stack page, so it can grow downwards */ sp = (unsigned long)stack + UM_KERN_PAGE_SIZE; - flags = CLONE_FILES | SIGCHLD; + tramp_data.stack = (void *) stub_stack; + tramp_data.clone_sp = (void *) sp; + tramp_data.pid = -EINVAL; - /* clone into new userspace process */ - pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack); + /* first stage CLONE_VM clone using VFORK and no signal notification */ + pid = clone(userspace_tramp_clone_vm, (void *) sp, + CLONE_VM | CLONE_FILES | CLONE_VFORK, &tramp_data); if (pid < 0) { err = -errno; printk(UM_KERN_ERR "%s : clone failed, errno = %d\n", @@ -297,6 +327,21 @@ int start_userspace(unsigned long stub_stack) return err; } + n = waitpid(pid, &status, WUNTRACED | WNOHANG | __WCLONE); + if (n < 0 || !WIFEXITED(status) || WEXITSTATUS(status)) { + err = -errno; + printk(UM_KERN_ERR "%s : wait failed, errno = %d, status = %d\n", + __func__, n < 0 ? errno : 0, status); + goto out_kill; + } + + pid = tramp_data.pid; + if (pid < 0) { + printk(UM_KERN_ERR "%s : second clone failed, errno = %d\n", + __func__, -pid); + return pid; + } + do { CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL)); if (n < 0) { @@ -305,7 +350,7 @@ int start_userspace(unsigned long stub_stack) __func__, errno); goto out_kill; } - } while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGALRM)); + } while (WIFEXITED(status) && (WSTOPSIG(status) == SIGALRM)); if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) { err = -EINVAL; -- 2.45.1