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    Subject[PATCH 5.15 910/917] powerpc/64s/interrupt: Fix check_return_regs_valid() false positive
    Date
    From: Nicholas Piggin <npiggin@gmail.com>

    commit 4a5cb51f3db4be547225a4bce7a43d41b231382b upstream.

    The check_return_regs_valid() can cause a false positive if the return
    regs are marked as norestart and they are an HSRR type interrupt,
    because the low bit in the bottom of regs->trap causes interrupt type
    matching to fail.

    This can occcur for example on bare metal with a HV privileged doorbell
    interrupt that causes a signal, but do_signal returns early because
    get_signal() fails, and takes the "No signal to deliver" path. In this
    case no signal was delivered so the return location is not changed so
    return SRRs are not invalidated, yet set_trap_norestart is called, which
    messes up the match. Building go-1.16.6 is known to reproduce this.

    Fix it by using the TRAP() accessor which masks out the low bit.

    Fixes: 6eaaf9de3599 ("powerpc/64s/interrupt: Check and fix srr_valid without crashing")
    Cc: stable@vger.kernel.org # v5.14+
    Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/20211026122531.3599918-1-npiggin@gmail.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/powerpc/kernel/interrupt.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/powerpc/kernel/interrupt.c
    +++ b/arch/powerpc/kernel/interrupt.c
    @@ -266,7 +266,7 @@ static void check_return_regs_valid(stru
    if (trap_is_scv(regs))
    return;

    - trap = regs->trap;
    + trap = TRAP(regs);
    // EE in HV mode sets HSRRs like 0xea0
    if (cpu_has_feature(CPU_FTR_HVMODE) && trap == INTERRUPT_EXTERNAL)
    trap = 0xea0;

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