CVE-2026-72292: KVM: s390: Initialize KVM_S390_GET_CMMA_BITS memory

CVE-2026-72292: KVM: s390: Initialize KVM_S390_GET_CMMA_BITS memory

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

KVM: s390: Initialize KVM_S390_GET_CMMA_BITS memory

kvm_s390_get_cmma_bits() allocates its output buffer with vmalloc(),
which does not zero the returned pages:

	values = vmalloc(args->count);

In the non-peek (migration) path, dat_get_cmma() reports a byte count
spanning from the first to the last dirty page, but __dat_get_cmma_pte()
writes values[gfn - start] only for pages whose CMMA dirty bit is set.
The walk uses DAT_WALK_IGN_HOLES, so clean and unmapped pages that lie
between two dirty pages within the reported span are visited but never
store their byte.  Those gaps (up to KVM_S390_MAX_BIT_DISTANCE pages
each) stay uninitialized yet fall inside [0, count) and are copied out
by copy_to_user(), disclosing stale kernel memory to user space.

Before the switch to the new gmap implementation the buffer was fully
populated for every gfn in the span, so no uninitialized bytes were
exposed; the dirty-only walk introduced the leak.

Use vzalloc() so the gaps read back as zero.

The Linux kernel CVE team has assigned CVE-2026-72292 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 7.0 with commit e38c884df92119d96f652d51f82661dd2fc0b885 and fixed in 7.1.5 with commit a4a19941ccb2164edc3491faa5ac5df82e94b363
	Issue introduced in 7.0 with commit e38c884df92119d96f652d51f82661dd2fc0b885 and fixed in 7.2-rc1 with commit c7dda3d0f869dc97223448a06c9a2e5235928e48

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-72292
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	arch/s390/kvm/kvm-s390.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/a4a19941ccb2164edc3491faa5ac5df82e94b363
	https://git.kernel.org/stable/c/c7dda3d0f869dc97223448a06c9a2e5235928e48