CVE-2026-90195: riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args

CVE-2026-90195: riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args

[Greg Kroah-Hartman]

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

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

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

riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args

On RV64, the ABI requires sign-extension for signed 1-byte and 2-byte kfunc
args. However, the RV64 JIT currently does not perform sign-extension for
such kfunc args.

Before commit 7ce090afbf72 ("bpf: Infer zext_dst based on static register
liveness analysis"), state pruning could potentially omit zero-extension
of 32-bit subregisters, which inadvertently masked the above issue by making
the args appear as if they had been properly sign-extended. After that
commit, the problem is exposed, causing the kfunc_call/kfunc_call_test4
selftest to fail.

Fix this by extending the existing sign-extension logic to handle signed
1-byte and 2-byte kfunc args as well.

The Linux kernel CVE team has assigned CVE-2026-90195 to this issue.


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

	Issue introduced in 6.9 with commit 443574b033876c85a35de4c65c14f7fe092222b2 and fixed in 6.12.110 with commit 555fc6f1caf00ce7005e732b688da26c0dc3c5c5
	Issue introduced in 6.9 with commit 443574b033876c85a35de4c65c14f7fe092222b2 and fixed in 6.18.52 with commit 801ae90f8ce099187e6224cec7d72d07a4df0324
	Issue introduced in 6.9 with commit 443574b033876c85a35de4c65c14f7fe092222b2 and fixed in 7.2.6 with commit 71dbd143be598954ae103feadd12692aeb0f2f88
	Issue introduced in 6.9 with commit 443574b033876c85a35de4c65c14f7fe092222b2 and fixed in 7.3-rc1 with commit f2aaa621591093cfe8224a25ef2f04a3b1e304b0

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-2026-90195
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/riscv/net/bpf_jit_comp64.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/555fc6f1caf00ce7005e732b688da26c0dc3c5c5
	https://git.kernel.org/stable/c/801ae90f8ce099187e6224cec7d72d07a4df0324
	https://git.kernel.org/stable/c/71dbd143be598954ae103feadd12692aeb0f2f88
	https://git.kernel.org/stable/c/f2aaa621591093cfe8224a25ef2f04a3b1e304b0