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powerpc/64: Fix msr_check_and_set/clear MSR[EE] race

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irq soft-masking means that when Linux irqs are disabled, the MSR[EE]
value can change from 1 to 0 asynchronously: if a masked interrupt of
the PACA_IRQ_MUST_HARD_MASK variety fires while irqs are disabled,
the masked handler will return with MSR[EE]=0.

This means a sequence like mtmsr(mfmsr() | MSR_FP) is racy if it can
be called with local irqs disabled, unless a hard_irq_disable has been
done.

Reported-by: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221004051157.308999-2-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2022-10-04 15:11:57 +10:00 committed by Michael Ellerman
parent 8154850b28
commit 0fa6831811
2 changed files with 26 additions and 2 deletions
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24
arch/powerpc/include/asm/hw_irq.h
View file

@ -471,6 +471,30 @@ static inline void irq_soft_mask_regs_set_state(struct pt_regs *regs, unsigned l
}
#endif /* CONFIG_PPC64 */
static inline unsigned long mtmsr_isync_irqsafe(unsigned long msr)
{
#ifdef CONFIG_PPC64
if (arch_irqs_disabled()) {
/*
* With soft-masking, MSR[EE] can change from 1 to 0
* asynchronously when irqs are disabled, and we don't want to
* set MSR[EE] back to 1 here if that has happened. A race-free
* way to do this is ensure EE is already 0. Another way it
* could be done is with a RESTART_TABLE handler, but that's
* probably overkill here.
*/
msr &= ~MSR_EE;
mtmsr_isync(msr);
irq_soft_mask_set(IRQS_ALL_DISABLED);
local_paca->irq_happened |= PACA_IRQ_HARD_DIS;
} else
#endif
mtmsr_isync(msr);
return msr;
}
#define ARCH_IRQ_INIT_FLAGS IRQ_NOREQUEST
#endif /* __ASSEMBLY__ */

4
arch/powerpc/kernel/process.c
View file

@ -127,7 +127,7 @@ unsigned long notrace msr_check_and_set(unsigned long bits)
newmsr |= MSR_VSX;
if (oldmsr != newmsr)
mtmsr_isync(newmsr);
newmsr = mtmsr_isync_irqsafe(newmsr);
return newmsr;
}
@ -145,7 +145,7 @@ void notrace __msr_check_and_clear(unsigned long bits)
newmsr &= ~MSR_VSX;
if (oldmsr != newmsr)
mtmsr_isync(newmsr);
mtmsr_isync_irqsafe(newmsr);
}
EXPORT_SYMBOL(__msr_check_and_clear);