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authorFrederic Weisbecker <fweisbec@gmail.com>2015-05-06 18:04:23 +0200
committerIngo Molnar <mingo@kernel.org>2015-05-07 12:02:50 +0200
commitaed5ed47724f6a7453fa62e3c90f3cee93edbfe3 (patch)
tree216d3c4a8d7bfa2204052e89790f352ad0dcd1c1 /kernel/context_tracking.c
parent0e1dc4274828f64fcb56fc7b950acdc5ff7a395f (diff)
downloadlinux-sh-aed5ed47724f6a7453fa62e3c90f3cee93edbfe3.tar.gz
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 <davej@redhat.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Reviewed-by: Rik van Riel <riel@redhat.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Chris Metcalf <cmetcalf@ezchip.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Mike Galbraith <umgwanakikbuti@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Rafael J . Wysocki <rafael.j.wysocki@intel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1430928266-24888-2-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/context_tracking.c')
-rw-r--r--kernel/context_tracking.c29
1 files changed, 29 insertions, 0 deletions
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);