Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754224AbbEKSAz (ORCPT ); Mon, 11 May 2015 14:00:55 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36534 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753269AbbEKR4M (ORCPT ); Mon, 11 May 2015 13:56:12 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Alexey Brodkin , Vineet Gupta Subject: [PATCH 3.14 25/25] ARC: signal handling robustify Date: Mon, 11 May 2015 10:55:26 -0700 Message-Id: <20150511175450.791899865@linuxfoundation.org> X-Mailer: git-send-email 2.4.0 In-Reply-To: <20150511175450.007060990@linuxfoundation.org> References: <20150511175450.007060990@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3323 Lines: 105 3.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Vineet Gupta commit e4140819dadc3624accac8294881bca8a3cba4ed upstream. A malicious signal handler / restorer can DOS the system by fudging the user regs saved on stack, causing weird things such as sigreturn returning to user mode PC but cpu state still being kernel mode.... Ensure that in sigreturn path status32 always has U bit; any other bogosity (gargbage PC etc) will be taken care of by normal user mode exceptions mechanisms. Reproducer signal handler: void handle_sig(int signo, siginfo_t *info, void *context) { ucontext_t *uc = context; struct user_regs_struct *regs = &(uc->uc_mcontext.regs); regs->scratch.status32 = 0; } Before the fix, kernel would go off to weeds like below: --------->8----------- [ARCLinux]$ ./signal-test Path: /signal-test CPU: 0 PID: 61 Comm: signal-test Not tainted 4.0.0-rc5+ #65 task: 8f177880 ti: 5ffe6000 task.ti: 8f15c000 [ECR ]: 0x00220200 => Invalid Write @ 0x00000010 by insn @ 0x00010698 [EFA ]: 0x00000010 [BLINK ]: 0x2007c1ee [ERET ]: 0x10698 [STAT32]: 0x00000000 : <-------- BTA: 0x00010680 SP: 0x5ffe7e48 FP: 0x00000000 LPS: 0x20003c6c LPE: 0x20003c70 LPC: 0x00000000 ... --------->8----------- Reported-by: Alexey Brodkin Signed-off-by: Vineet Gupta Signed-off-by: Greg Kroah-Hartman --- arch/arc/kernel/signal.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) --- a/arch/arc/kernel/signal.c +++ b/arch/arc/kernel/signal.c @@ -131,6 +131,15 @@ SYSCALL_DEFINE0(rt_sigreturn) /* Don't restart from sigreturn */ syscall_wont_restart(regs); + /* + * Ensure that sigreturn always returns to user mode (in case the + * regs saved on user stack got fudged between save and sigreturn) + * Otherwise it is easy to panic the kernel with a custom + * signal handler and/or restorer which clobberes the status32/ret + * to return to a bogus location in kernel mode. + */ + regs->status32 |= STATUS_U_MASK; + return regs->r0; badframe: @@ -234,8 +243,11 @@ setup_rt_frame(int signo, struct k_sigac /* * handler returns using sigreturn stub provided already by userpsace + * If not, nuke the process right away */ - BUG_ON(!(ka->sa.sa_flags & SA_RESTORER)); + if(!(ka->sa.sa_flags & SA_RESTORER)) + return 1; + regs->blink = (unsigned long)ka->sa.sa_restorer; /* User Stack for signal handler will be above the frame just carved */ @@ -302,12 +314,12 @@ handle_signal(unsigned long sig, struct struct pt_regs *regs) { sigset_t *oldset = sigmask_to_save(); - int ret; + int failed; /* Set up the stack frame */ - ret = setup_rt_frame(sig, ka, info, oldset, regs); + failed = setup_rt_frame(sig, ka, info, oldset, regs); - if (ret) + if (failed) force_sigsegv(sig, current); else signal_delivered(sig, info, ka, regs, 0); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/