s390/sclp: fix Secure-IPL facility detection

Prevent out-of-range access if the returned SCLP SCCB response is smaller
in size than the address of the Secure-IPL flag.

Fixes: c9896acc7851 ("s390/ipl: Provide has_secure sysfs attribute")
Cc: stable@vger.kernel.org # 5.2+
Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

diff --git a/drivers/s390/char/sclp_early.c b/drivers/s390/char/sclp_early.c
index 2f3515f..f3d5c7f 100644 (file)
--- a/drivers/s390/char/sclp_early.c
+++ b/drivers/s390/char/sclp_early.c
@@ -45,13 +45,14 @@ static void __init sclp_early_facilities_detect(void)
        sclp.has_gisaf = !!(sccb->fac118 & 0x08);
        sclp.has_hvs = !!(sccb->fac119 & 0x80);
        sclp.has_kss = !!(sccb->fac98 & 0x01);
-       sclp.has_sipl = !!(sccb->cbl & 0x4000);
        if (sccb->fac85 & 0x02)
                S390_lowcore.machine_flags |= MACHINE_FLAG_ESOP;
        if (sccb->fac91 & 0x40)
                S390_lowcore.machine_flags |= MACHINE_FLAG_TLB_GUEST;
        if (sccb->cpuoff > 134)
                sclp.has_diag318 = !!(sccb->byte_134 & 0x80);
+       if (sccb->cpuoff > 137)
+               sclp.has_sipl = !!(sccb->cbl & 0x4000);
        sclp.rnmax = sccb->rnmax ? sccb->rnmax : sccb->rnmax2;
        sclp.rzm = sccb->rnsize ? sccb->rnsize : sccb->rnsize2;
        sclp.rzm <<= 20;