From aed5ed47724f6a7453fa62e3c90f3cee93edbfe3 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 6 May 2015 18:04:23 +0200 Subject: [PATCH] context_tracking: Protect against recursion 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 Signed-off-by: Frederic Weisbecker Reviewed-by: Rik van Riel Acked-by: Peter Zijlstra (Intel) Cc: Borislav Petkov Cc: Chris Metcalf Cc: H. Peter Anvin Cc: Martin Schwidefsky Cc: Mike Galbraith Cc: Oleg Nesterov Cc: Paul E. McKenney Cc: Rafael J . Wysocki Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1430928266-24888-2-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar --- include/linux/context_tracking_state.h | 1 + kernel/context_tracking.c | 29 ++++++++++++++++++++++++++ 2 files changed, 30 insertions(+) diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h index 6b7b96a32b75..678ecdf90cf6 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 72d59a1a6eb6..5b11a10e196a 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 +94,9 @@ void context_tracking_enter(enum ctx_state state) WARN_ON_ONCE(!current->mm); local_irq_save(flags); + if (!context_tracking_recursion_enter()) + goto out_irq_restore; + if ( __this_cpu_read(context_tracking.state) != state) { if (__this_cpu_read(context_tracking.active)) { /* @@ -105,6 +127,8 @@ void context_tracking_enter(enum ctx_state state) */ __this_cpu_write(context_tracking.state, state); } + context_tracking_recursion_exit(); +out_irq_restore: local_irq_restore(flags); } NOKPROBE_SYMBOL(context_tracking_enter); @@ -139,6 +163,9 @@ void context_tracking_exit(enum ctx_state state) return; local_irq_save(flags); + if (!context_tracking_recursion_enter()) + goto out_irq_restore; + if (__this_cpu_read(context_tracking.state) == state) { if (__this_cpu_read(context_tracking.active)) { /* @@ -153,6 +180,8 @@ void context_tracking_exit(enum ctx_state state) } __this_cpu_write(context_tracking.state, CONTEXT_KERNEL); } + context_tracking_recursion_exit(); +out_irq_restore: local_irq_restore(flags); } NOKPROBE_SYMBOL(context_tracking_exit); -- 2.20.1