Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [PATCH 1/4] context_tracking: Protect against recursion | Date | Fri, 24 Apr 2015 17:58:28 +0200 |
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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 <davej@redhat.com> Reviewed-by: Rik van Riel <riel@redhat.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Dave Jones <davej@redhat.com> Cc: Oleg Nesterov <oleg@redhat.com> --- 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
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