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    Subject[PATCH 5.15 559/667] s390/perf: obtain sie_block from the right address
    Date
    From: Nico Boehr <nrb@linux.ibm.com>

    commit c9bfb460c3e4da2462e16b0f0b200990b36b1dd2 upstream.

    Since commit 1179f170b6f0 ("s390: fix fpu restore in entry.S"), the
    sie_block pointer is located at empty1[1], but in sie_block() it was
    taken from empty1[0].

    This leads to a random pointer being dereferenced, possibly causing
    system crash.

    This problem can be observed when running a simple guest with an endless
    loop and recording the cpu-clock event:

    sudo perf kvm --guestvmlinux=<guestkernel> --guest top -e cpu-clock

    With this fix, the correct guest address is shown.

    Fixes: 1179f170b6f0 ("s390: fix fpu restore in entry.S")
    Cc: stable@vger.kernel.org
    Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
    Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
    Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
    Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
    Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/s390/kernel/perf_event.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/s390/kernel/perf_event.c
    +++ b/arch/s390/kernel/perf_event.c
    @@ -30,7 +30,7 @@ static struct kvm_s390_sie_block *sie_bl
    if (!stack)
    return NULL;

    - return (struct kvm_s390_sie_block *) stack->empty1[0];
    + return (struct kvm_s390_sie_block *)stack->empty1[1];
    }

    static bool is_in_guest(struct pt_regs *regs)

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