Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936450AbdCJMKJ (ORCPT ); Fri, 10 Mar 2017 07:10:09 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:45028 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935200AbdCJMKH (ORCPT ); Fri, 10 Mar 2017 07:10:07 -0500 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, "Will Deacon" , "Mark Salter" , "Catalin Marinas" , "Mark Rutland" Date: Fri, 10 Mar 2017 11:46:23 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 241/370] arm64: avoid returning from bad_mode In-Reply-To: X-SA-Exim-Connect-IP: 82.70.136.246 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 Content-Length: 3602 Lines: 105 3.16.42-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Mark Rutland commit 7d9e8f71b989230bc613d121ca38507d34ada849 upstream. Generally, taking an unexpected exception should be a fatal event, and bad_mode is intended to cater for this. However, it should be possible to contain unexpected synchronous exceptions from EL0 without bringing the kernel down, by sending a SIGILL to the task. We tried to apply this approach in commit 9955ac47f4ba1c95 ("arm64: don't kill the kernel on a bad esr from el0"), by sending a signal for any bad_mode call resulting from an EL0 exception. However, this also applies to other unexpected exceptions, such as SError and FIQ. The entry paths for these exceptions branch to bad_mode without configuring the link register, and have no kernel_exit. Thus, if we take one of these exceptions from EL0, bad_mode will eventually return to the original user link register value. This patch fixes this by introducing a new bad_el0_sync handler to cater for the recoverable case, and restoring bad_mode to its original state, whereby it calls panic() and never returns. The recoverable case branches to bad_el0_sync with a bl, and returns to userspace via the usual ret_to_user mechanism. Signed-off-by: Mark Rutland Fixes: 9955ac47f4ba1c95 ("arm64: don't kill the kernel on a bad esr from el0") Reported-by: Mark Salter Cc: Will Deacon Signed-off-by: Catalin Marinas [bwh: Backported to 3.16: - Leave type out of the log message as we don't have esr_get_class_string() - Adjust context] Signed-off-by: Ben Hutchings --- arch/arm64/kernel/entry.S | 2 +- arch/arm64/kernel/traps.c | 28 ++++++++++++++++++++++++---- 2 files changed, 25 insertions(+), 5 deletions(-) --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -491,7 +491,7 @@ el0_inv: mov x0, sp mov x1, #BAD_SYNC mrs x2, esr_el1 - b bad_mode + b bad_el0_sync ENDPROC(el0_sync) .align 6 --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -309,16 +309,33 @@ asmlinkage long do_ni_syscall(struct pt_ } /* - * bad_mode handles the impossible case in the exception vector. + * bad_mode handles the impossible case in the exception vector. This is always + * fatal. */ asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr) { - siginfo_t info; - void __user *pc = (void __user *)instruction_pointer(regs); console_verbose(); pr_crit("Bad mode in %s handler detected, code 0x%08x\n", handler[reason], esr); + + die("Oops - bad mode", regs, 0); + local_irq_disable(); + panic("bad mode"); +} + +/* + * bad_el0_sync handles unexpected, but potentially recoverable synchronous + * exceptions taken from EL0. Unlike bad_mode, this returns. + */ +asmlinkage void bad_el0_sync(struct pt_regs *regs, int reason, unsigned int esr) +{ + siginfo_t info; + void __user *pc = (void __user *)instruction_pointer(regs); + console_verbose(); + + pr_crit("Bad EL0 synchronous exception detected on CPU%d, code 0x%08x\n", + smp_processor_id(), esr); __show_regs(regs); info.si_signo = SIGILL; @@ -326,7 +343,10 @@ asmlinkage void bad_mode(struct pt_regs info.si_code = ILL_ILLOPC; info.si_addr = pc; - arm64_notify_die("Oops - bad mode", regs, &info, 0); + current->thread.fault_address = 0; + current->thread.fault_code = 0; + + force_sig_info(info.si_signo, &info, current); } void __pte_error(const char *file, int line, unsigned long val)