Commit 0fa68318 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

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



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: default avatarSachin Sant <sachinp@linux.ibm.com>
Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221004051157.308999-2-npiggin@gmail.com
parent 8154850b

arch/powerpc/include/asm/hw_irq.h

+24 −0
Original line number Diff line number Diff line
@@ -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__ */

arch/powerpc/kernel/process.c

+2 −2
Original line number Diff line number Diff line
@@ -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);