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s390x/sclp: reject invalid write event data headers

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If a guest submits an sccb with a tiny header length but a large number
of event mask entries, the write_event_mask handler will
1. return the wrong RC (ok instead of error)
2. write to memory after the allocated sccb in qemu host memory.

Add the necessary checks.

Cc: qemu-stable@nongnu.org
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Message-ID: <20260707070728.147203-2-borntraeger@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
This commit is contained in:
Christian Borntraeger
2026-07-07 09:07:24 +02:00
committed by Cornelia Huck
parent fbd0f95225
commit d88cd8f557
1 changed files with 6 additions and 0 deletions
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6
hw/s390x/event-facility.c
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@@ -286,6 +286,7 @@ static void read_event_data(SCLPEventFacility *ef, SCCB *sccb)
static void write_event_mask(SCLPEventFacility *ef, SCCB *sccb)
{
WriteEventMask *we_mask = (WriteEventMask *) sccb;
uint16_t sccb_length = be16_to_cpu(sccb->h.length);
uint16_t mask_length = be16_to_cpu(we_mask->mask_length);
sccb_mask_t tmp_mask;
@@ -294,6 +295,11 @@ static void write_event_mask(SCLPEventFacility *ef, SCCB *sccb)
return;
}
if (sccb_length < sizeof(WriteEventMask) + 4 * mask_length) {
sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH);
return;
}
/*
* Note: We currently only support masks up to 8 byte length;
* the remainder is filled up with zeroes. Older Linux