CVE-2026-98713: KVM: arm64: Apply the fine-grained UNDEFs without FEAT_FGT

CVE-2026-98713: KVM: arm64: Apply the fine-grained UNDEFs without FEAT_FGT

[Greg Kroah-Hartman]

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

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

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

KVM: arm64: Apply the fine-grained UNDEFs without FEAT_FGT

FGUs don't actually require hardware support, so don't gate fgt trap
config insertion on FGT. This is the only action required to allow FGUs
always, as kvm_calculate_traps() already computes the FGU bits with or
without FEAT_FGT.

This also fixes a spurious WARN when a TLBI OS is run on a guest in vEL1
without FEAT_TLBIOS on non FEAT_FGT hardware. In this configuration the
course-grained HCR_EL2.TTLBOS trap reaches the handler handle_tlbi_el1(),
which expects an EL1 TLBI only from vEL2. With FGUs enabled the UNDEF
will be injected without needing the specific handler.

[oliver: Take Wei-Lin's suggested changelog]

The Linux kernel CVE team has assigned CVE-2026-98713 to this issue.


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

	Issue introduced in 6.9 with commit f5a5a406b4b8bb6c1fc7a1e92a872bd86061a53f and fixed in 6.12.113 with commit 2f4a15c52a552c5244ec27f4ca8bda855594f918
	Issue introduced in 6.9 with commit f5a5a406b4b8bb6c1fc7a1e92a872bd86061a53f and fixed in 6.18.56 with commit 1113374a17d7f7d16b02ee0bbd9b1e7a60cbb087
	Issue introduced in 6.9 with commit f5a5a406b4b8bb6c1fc7a1e92a872bd86061a53f and fixed in 7.2.10 with commit af3300b3a6bace925a496f3520e171c07b999c72
	Issue introduced in 6.9 with commit f5a5a406b4b8bb6c1fc7a1e92a872bd86061a53f and fixed in 7.3-rc6 with commit 4bdd2b3a708c1feb701cb8b62feb8ad2fd77bb07

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-2026-98713
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/arm64/kvm/emulate-nested.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/2f4a15c52a552c5244ec27f4ca8bda855594f918
	https://git.kernel.org/stable/c/1113374a17d7f7d16b02ee0bbd9b1e7a60cbb087
	https://git.kernel.org/stable/c/af3300b3a6bace925a496f3520e171c07b999c72
	https://git.kernel.org/stable/c/4bdd2b3a708c1feb701cb8b62feb8ad2fd77bb07