From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932167AbcHMRwx (ORCPT ); Sat, 13 Aug 2016 13:52:53 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:40818 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753135AbcHMRwv (ORCPT ); Sat, 13 Aug 2016 13:52:51 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, linux-mips@linux-mips.org, "Leonid Yegoshin" , "James Hogan" , "Ralf Baechle" Date: Sat, 13 Aug 2016 18:42:51 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 053/305] MIPS: Don't unwind to user mode with EVA In-Reply-To: X-SA-Exim-Connect-IP: 92.40.249.202 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.37-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: James Hogan commit a816b306c62195b7c43c92cb13330821a96bdc27 upstream. When unwinding through IRQs and exceptions, the unwinding only continues if the PC is a kernel text address, however since EVA it is possible for user and kernel address ranges to overlap, potentially allowing unwinding to continue to user mode if the user PC happens to be in the kernel text address range. Adjust the check to also ensure that the register state from before the exception is actually running in kernel mode, i.e. !user_mode(regs). I don't believe any harm can come of this problem, since the PC is only output, the stack pointer is checked to ensure it resides within the task's stack page before it is dereferenced in search of the return address, and the return address register is similarly only output (if the PC is in a leaf function or the beginning of a non-leaf function). However unwind_stack() is only meant for unwinding kernel code, so to be correct the unwind should stop there. Signed-off-by: James Hogan Reviewed-by: Leonid Yegoshin Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/11700/ Signed-off-by: Ralf Baechle Signed-off-by: Ben Hutchings --- arch/mips/kernel/process.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/mips/kernel/process.c +++ b/arch/mips/kernel/process.c @@ -489,7 +489,7 @@ unsigned long notrace unwind_stack_by_ad *sp + sizeof(*regs) <= stack_page + THREAD_SIZE - 32) { regs = (struct pt_regs *)*sp; pc = regs->cp0_epc; - if (__kernel_text_address(pc)) { + if (!user_mode(regs) && __kernel_text_address(pc)) { *sp = regs->regs[29]; *ra = regs->regs[31]; return pc;