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LoongArch: Do not save/restore percpu base register in rethook trampoline

Type: advisorySource: Official CVE List1 source record

In the Linux kernel, the following vulnerability has been resolved: LoongArch: Do not save/restore percpu base register in rethook trampoline The rethook trampoline saves $r21 ($u0), the percpu base, into its frame at entry and restores it at exit. Inbetween rethook_trampoline_handler() may schedule via preempt_enable_notrace(). If the task migrates to another CPU, the frame's $r21 holds the old CPU's percpu base, and restoring it poisons $r21 on the new CPU. Until the next user->kernel transition heals $r21, all this_cpu_*() accesses (runqueues, RCU per-CPU data, timer tick programming, FPU ownership) hit the wrong CPU's percpu area. Under kretprobe-heavy preemptible load this can corrupt scheduler and timer state: scheduling-while-atomic splats, wrong-CPU RCU warnings, WARN_ON_ONCE(rq != this_rq()) in nohz_balance_exit_idle(), and CPUs parking in the idle loop with the constant timer never re-armed (hard lockup). Reproduces on a Loongson-3A6000 with kretprobes on VFS paths plus heavy file churn (OS install / unsquashfs). By convention $r21 always holds the current CPU's percpu base in kernel mode: SAVE_SOME() at exception entry reloads it only when coming from user mode, and RESTORE_SOME() restores it only when returning to user mode; the context-switch path never writes it. Therefore the live $r21 at trampoline exit is already correct, and nothing inbetween can change it legitimately (kernel C code cannot write a global register variable). The same flaw existed even in the

Announced Source revision 1
Original source ↗

CVE-2026-89903

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-89903

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "3f5536860086d906b01ec5ed68cf50c7edcc40af",
        "lessThan": "a03b5e7483ad2c33ba5dd2adb8552e84bfee8fe2",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "3f5536860086d906b01ec5ed68cf50c7edcc40af",
        "lessThan": "8f15e95b438bc6b3c9f23a33c9a0d0678ebd1dc8",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "3f5536860086d906b01ec5ed68cf50c7edcc40af",
        "lessThan": "266ffc92e68593759adfe3d58f188773d32782c3",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "3f5536860086d906b01ec5ed68cf50c7edcc40af",
        "lessThan": "c048b0a3c0836c4b1bef4b51d355d27090bf6790",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "3f5536860086d906b01ec5ed68cf50c7edcc40af",
        "lessThan": "c3f2feace5e4f4b01b68b9f947b19adb4155c32e",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "arch/loongarch/kernel/rethook_trampoline.S"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "6.3"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "6.3",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "6.6.157",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.110",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.18.51",
        "versionType": "semver",
        "lessThanOrEqual": "6.18.*"
      },
      {
        "status": "unaffected",
        "version": "7.2.5",
        "versionType": "semver",
        "lessThanOrEqual": "7.2.*"
      },
      {
        "status": "unaffected",
        "version": "7.3",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "arch/loongarch/kernel/rethook_trampoline.S"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2026-89903

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#36352 · Revision 1
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Publisher date
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