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 64F0AC25B7E for ; Tue, 28 May 2024 08:54:43 +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=wi2Xld7h/j0VXvio5/oyj4J7kJTuo4AEFW3Ce6k+E28=; b=yPrwTJXAHy3TCi2i95Ll/644XS KYlaO7WaFtbqcZvvSICmG8YdzSudK0Up/tXfs7mMrnHBzRo0PeHyTj2fl7jqQeH7vKLiqTVxPimdY +VhrEIFWZOFwsyBQ1878MRAVPJor8e7wuxdfU6jtAbUaqi8frFPaO12fchy0Q4GgvZec2q6vA+pS9 xbpPEmZxWhy2p8j3sBiUSB4Fe/8DEVZ2EuENL0D35n/U8b4mka1QNp4OxordRIbt77CXjx+3UMZwG UUcmtUKangQr5zwjICeysyhuV8vnd8JZRDjspZT14bt3fUSr99UievSz+jtk0EULqToB5/1JmXa0b 9z/3MzBw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sBsbT-0000000HY6D-0BFR; Tue, 28 May 2024 08:54:43 +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 1sBsbQ-0000000HY4o-0uVA for linux-um@lists.infradead.org; Tue, 28 May 2024 08:54:41 +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=wi2Xld7h/j0VXvio5/oyj4J7kJTuo4AEFW3Ce6k+E28=; t=1716886480; x=1718096080; b=P13zEp10MO5n8TeMAmvsbEcG8pg2hmaGPW+Ocoru895anQW tCuQS4YkBFMn9gKriJhgIYNtpmvh+onFQkRqjPafOM+/qJAe6Wjt9Gs2sqi61QqPLQWWYQWjGmhF+ t2AFQweWH252RV4DcbzzQ/8yMxqY7iQEHT2NsoZfYZGXFEnIQl9yyB6zmx62hTxUcEk2BTdNPtqvz LjrG6tJilPPFYacmVEMDklMTPYONG9Xo1Y5sxCaQjTMCOzuHYf99lKMRckWeplk1Dvt4ky5onIYJ/ Ax8zDNkLiEOGkugCTcyqvcDdl2tvMGYg5+5sgRJFILrYXEEo+KqAg2e/9YHWM9cQ==; Received: by sipsolutions.net with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.97) (envelope-from ) id 1sBsbN-0000000EAlo-0dfv; Tue, 28 May 2024 10:54:38 +0200 From: benjamin@sipsolutions.net To: linux-um@lists.infradead.org Cc: Benjamin Berg Subject: [PATCH 3/5] um: Do a double clone to disable rseq Date: Tue, 28 May 2024 10:54:17 +0200 Message-ID: <20240528085419.1964424-4-benjamin@sipsolutions.net> X-Mailer: git-send-email 2.45.1 In-Reply-To: <20240528085419.1964424-1-benjamin@sipsolutions.net> References: <20240528085419.1964424-1-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-20240528_015440_286378_D0C22E1B X-CRM114-Status: GOOD ( 17.25 ) 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 --- arch/um/os-Linux/skas/process.c | 54 ++++++++++++++++++++++++++++++--- 1 file changed, 50 insertions(+), 4 deletions(-) diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c index 41a288dcfc34..ee332a2aeea6 100644 --- a/arch/um/os-Linux/skas/process.c +++ b/arch/um/os-Linux/skas/process.c @@ -255,6 +255,31 @@ 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; + + /* + * This helper exist to do a double-clone. First with CLONE_VM which + * effectively disables things like rseq, and then the second one to + * get a new memory space. + */ + + 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 +293,10 @@ 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 +312,13 @@ 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); + pid = clone(userspace_tramp_clone_vm, (void *) sp, + CLONE_VM | CLONE_FILES | SIGCHLD, &tramp_data); if (pid < 0) { err = -errno; printk(UM_KERN_ERR "%s : clone failed, errno = %d\n", @@ -305,7 +334,24 @@ int start_userspace(unsigned long stub_stack) __func__, errno); goto out_kill; } - } while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGALRM)); + } while (!WIFEXITED(status)); + + 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) { + err = -errno; + printk(UM_KERN_ERR "%s : wait failed, errno = %d\n", + __func__, errno); + goto out_kill; + } + } while (WIFEXITED(status) && (WSTOPSIG(status) == SIGALRM)); if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) { err = -EINVAL; -- 2.45.1