Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752103AbbEFQEo (ORCPT ); Wed, 6 May 2015 12:04:44 -0400 Received: from mail-wi0-f178.google.com ([209.85.212.178]:35841 "EHLO mail-wi0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750698AbbEFQEk (ORCPT ); Wed, 6 May 2015 12:04:40 -0400 From: Frederic Weisbecker To: Ingo Molnar Cc: LKML , Frederic Weisbecker , "Rafael J . Wysocki" , Peter Zijlstra , Mike Galbraith , Chris Metcalf , Dave Jones , Thomas Gleixner , Oleg Nesterov , "Paul E . McKenney" , Ingo Molnar , Rik van Riel , Martin Schwidefsky Subject: [PATCH 1/4] context_tracking: Protect against recursion Date: Wed, 6 May 2015 18:04:23 +0200 Message-Id: <1430928266-24888-2-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1430928266-24888-1-git-send-email-fweisbec@gmail.com> References: <1430928266-24888-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3795 Lines: 117 Context tracking recursion can happen when an exception triggers in the middle of a call to a context tracking probe. This special case can be caused by vmalloc faults. If an access to a memory area allocated by vmalloc happens in the middle of context_tracking_enter(), we may run into an endless fault loop because the exception in turn calls context_tracking_enter() which faults on the same vmalloc'ed memory, triggering an exception again, etc... Some rare crashes have been reported so lets protect against this with a recursion counter. Reported-by: Dave Jones Reviewed-by: Rik van Riel Acked-by: Peter Zijlstra (Intel) Signed-off-by: Frederic Weisbecker Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Rik van Riel Cc: Paul E. McKenney Cc: Ingo Molnar Cc: Dave Jones Cc: Oleg Nesterov --- include/linux/context_tracking_state.h | 1 + kernel/context_tracking.c | 30 ++++++++++++++++++++++++++++++ 2 files changed, 31 insertions(+) diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h index 6b7b96a..678ecdf 100644 --- a/include/linux/context_tracking_state.h +++ b/include/linux/context_tracking_state.h @@ -12,6 +12,7 @@ struct context_tracking { * may be further optimized using static keys. */ bool active; + int recursion; enum ctx_state { CONTEXT_KERNEL = 0, CONTEXT_USER, diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c index 72d59a1..b9e0b4f 100644 --- a/kernel/context_tracking.c +++ b/kernel/context_tracking.c @@ -38,6 +38,25 @@ void context_tracking_cpu_set(int cpu) } } +static bool context_tracking_recursion_enter(void) +{ + int recursion; + + recursion = __this_cpu_inc_return(context_tracking.recursion); + if (recursion == 1) + return true; + + WARN_ONCE((recursion < 1), "Invalid context tracking recursion value %d\n", recursion); + __this_cpu_dec(context_tracking.recursion); + + return false; +} + +static void context_tracking_recursion_exit(void) +{ + __this_cpu_dec(context_tracking.recursion); +} + /** * context_tracking_enter - Inform the context tracking that the CPU is going * enter user or guest space mode. @@ -75,6 +94,11 @@ void context_tracking_enter(enum ctx_state state) WARN_ON_ONCE(!current->mm); local_irq_save(flags); + if (!context_tracking_recursion_enter()) { + local_irq_restore(flags); + return; + } + if ( __this_cpu_read(context_tracking.state) != state) { if (__this_cpu_read(context_tracking.active)) { /* @@ -105,6 +129,7 @@ void context_tracking_enter(enum ctx_state state) */ __this_cpu_write(context_tracking.state, state); } + context_tracking_recursion_exit(); local_irq_restore(flags); } NOKPROBE_SYMBOL(context_tracking_enter); @@ -139,6 +164,10 @@ void context_tracking_exit(enum ctx_state state) return; local_irq_save(flags); + if (!context_tracking_recursion_enter()) { + local_irq_restore(flags); + return; + } if (__this_cpu_read(context_tracking.state) == state) { if (__this_cpu_read(context_tracking.active)) { /* @@ -153,6 +182,7 @@ void context_tracking_exit(enum ctx_state state) } __this_cpu_write(context_tracking.state, CONTEXT_KERNEL); } + context_tracking_recursion_exit(); local_irq_restore(flags); } NOKPROBE_SYMBOL(context_tracking_exit); -- 2.1.4 -- 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/