powerpc/64s/interrupt: Fix interrupt exit race with security mitigation switch
authorNicholas Piggin <npiggin@gmail.com>
Mon, 6 Feb 2023 04:22:40 +0000 (14:22 +1000)
committerMichael Ellerman <mpe@ellerman.id.au>
Mon, 6 Feb 2023 23:13:33 +0000 (10:13 +1100)
commit2ea31e2e62bbc4d11c411eeb36f1b02841dbcab1
tree2670e8f5cbcc495e79be1835f8292c0bb573d470
parent97e45d469eb180a7bd2809e4e079331552c73e42
powerpc/64s/interrupt: Fix interrupt exit race with security mitigation switch

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
arch/powerpc/kernel/interrupt.c