Commit-ID: aed5ed47724f6a7453fa62e3c90f3cee93edbfe3
Gitweb: http://git.kernel.org/tip/aed5ed47724f6a7453fa62e3c90f3cee93edbfe3
Author: Frederic Weisbecker <fweisbec@xxxxxxxxx>
AuthorDate: Wed, 6 May 2015 18:04:23 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 7 May 2015 12:02:50 +0200
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@xxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Rafael J . Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1430928266-24888-2-git-send-email-fweisbec@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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 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..5b11a10 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);
--
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