From: Nicholas Piggin npiggin@gmail.com
commit 2ea31e2e62bbc4d11c411eeb36f1b02841dbcab1 upstream.
The RFI and STF security mitigation options can flip the interrupt_exit_not_reentrant static branch condition concurrently with the interrupt exit code which tests that branch.
Interrupt exit tests this condition to set MSR[EE|RI] for exit, then again in the case a soft-masked interrupt is found pending, to recover the MSR so the interrupt can be replayed before attempting to exit again. If the condition changes between these two tests, the MSR and irq soft-mask state will become corrupted, leading to warnings and possible crashes. For example, if the branch is initially true then false, MSR[EE] will be 0 but PACA_IRQ_HARD_DIS clear and EE may not get enabled, leading to warnings in irq_64.c.
Fixes: 13799748b957 ("powerpc/64: use interrupt restart table to speed up return from interrupt") Cc: stable@vger.kernel.org # v5.14+ Reported-by: Sachin Sant sachinp@linux.ibm.com Tested-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/20230206042240.92103-1-npiggin@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/kernel/interrupt.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c @@ -50,16 +50,18 @@ static inline bool exit_must_hard_disabl */ static notrace __always_inline bool prep_irq_for_enabled_exit(bool restartable) { + bool must_hard_disable = (exit_must_hard_disable() || !restartable); + /* This must be done with RI=1 because tracing may touch vmaps */ trace_hardirqs_on();
- if (exit_must_hard_disable() || !restartable) + if (must_hard_disable) __hard_EE_RI_disable();
#ifdef CONFIG_PPC64 /* This pattern matches prep_irq_for_idle */ if (unlikely(lazy_irq_pending_nocheck())) { - if (exit_must_hard_disable() || !restartable) { + if (must_hard_disable) { local_paca->irq_happened |= PACA_IRQ_HARD_DIS; __hard_RI_enable(); }