Merge: CVE-2025-39694: s390/sclp: Fix SCCB present check

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/7324

JIRA: https://issues.redhat.com/browse/RHEL-113559
CVE: CVE-2025-39694

```
commit 430fa71
Author: Peter Oberparleiter <oberpar@linux.ibm.com>
Date:   Mon Aug 18 12:21:52 2025 +0200

    s390/sclp: Fix SCCB present check

    Tracing code called by the SCLP interrupt handler contains early exits
    if the SCCB address associated with an interrupt is NULL. This check is
    performed after physical to virtual address translation.

    If the kernel identity mapping does not start at address zero, the
    resulting virtual address is never zero, so that the NULL checks won't
    work. Subsequently this may result in incorrect accesses to the first
    page of the identity mapping.

    Fix this by introducing a function that handles the NULL case before
    address translation.

    Fixes: ada1da3 ("s390/sclp: sort out physical vs virtual pointers usage")
    Cc: stable@vger.kernel.org
    Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
    Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
    Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
```

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

---

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Approved-by: Steve Best <sbest@redhat.com>
Approved-by: David Arcari <darcari@redhat.com>
Approved-by: Tony Camuso <tcamuso@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Patrick Talbert <ptalbert@redhat.com>

Author: ptalbert