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authorThomas Gleixner <tglx@linutronix.de>2010-12-16 14:25:18 +0100
committerThomas Gleixner <tglx@linutronix.de>2010-12-16 23:25:49 +0100
commit5fed714f43c07bb622426ccc4de8c8c7500cb148 (patch)
parent76bdf0c3151369f5b15af4baac2708e59347d664 (diff)
x86: stackprotector: Avoid random pool on rt
CPU bringup calls into the random pool to initialize the stack canary. During boot that works nicely even on RT as the might sleep checks are disabled. During CPU hotplug the might sleep checks trigger. Making the locks in random raw is a major PITA, so avoid the call on RT is the only sensible solution. This is basically the same randomness which we get during boot where the random pool has no entropy and we rely on the TSC randomnness. Reported-by: Carsten Emde <carsten.emde@osadl.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
1 files changed, 9 insertions, 1 deletions
diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
index 157517763565..4cf440fa63db 100644
--- a/arch/x86/include/asm/stackprotector.h
+++ b/arch/x86/include/asm/stackprotector.h
@@ -58,7 +58,7 @@
static __always_inline void boot_init_stack_canary(void)
- u64 canary;
+ u64 uninitialized_var(canary);
u64 tsc;
#ifdef CONFIG_X86_64
@@ -69,8 +69,16 @@ static __always_inline void boot_init_stack_canary(void)
* of randomness. The TSC only matters for very early init,
* there it already has some randomness on most systems. Later
* on during the bootup the random pool has true entropy too.
+ *
+ * For preempt-rt we need to weaken the randomness a bit, as
+ * we can't call into the random generator from atomic context
+ * due to locking constraints. We just leave canary
+ * uninitialized and use the TSC based randomness on top of
+ * it.
get_random_bytes(&canary, sizeof(canary));
tsc = __native_read_tsc();
canary += tsc + (tsc << 32UL);