Описание
In the Linux kernel, the following vulnerability has been resolved: x86/insn-eval: Fix shadowed segment index in get_seg_reg_override_idx() Commit 45e1dccc0653 ("x86/insn: Simplify for_each_insn_prefix()") made for_each_insn_prefix() declare its own loop counter named idx. get_seg_reg_override_idx() keeps its result in a local of the same name, so the assignments in the loop body now write the loop counter:
- the function always returns INAT_SEG_REG_DEFAULT, so FS and GS overrides are ignored;
- a CS override sets the counter to INAT_SEG_REG_CS (2), the increment
makes it 3, and prefixes.bytes[3] holds the last prefix, 0x2e again,
so the loop never terminates.
The UMIP emulation reaches this from the #GP handler for user space: an
SGDT, SIDT or SMSW with a memory operand and a CS prefix leaves the task
spinning in the kernel, never returning to user space, with a SIGKILL
that is never delivered. Any user can thus tie up CPUs until reboot.
With an FS or GS prefix, the emulated result is written to the wrong
address.
Rename the internal macro iterator variable.
[ Lukas' original patch renamed the use site, I changed it to rename the
iterator in the macro instead, but left Lukas' commit message and
authorship - Linus ]
A flaw was found in the Linux kernel's x86 instruction evaluation component. A local user can exploit this vulnerability to cause a Denial of Service (DoS) by executing instructions with segment register overrides that trigger an infinite loop during instruction decoding. This condition traps the processor core in kernel mode, tying up CPU resources until the system is rebooted. Additionally, improper segment prefix processing may cause emulated instruction results to be written to unintended memory locations.
Отчет
This vulnerability is rated as Moderate impact because an authenticated local unprivileged attacker can induce an infinite loop within the kernel to exhaust system CPU resources, but cannot directly escalate privileges or breach confidentiality. Exploitation occurs during user-space instruction emulation on x86 architectures when processing specific segment prefixes, resulting in core hangs that persist until the system is restarted. Because the attack vector is restricted to local access and does not allow remote exploitation, the overall operational risk remains bounded.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 10 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 6 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 7 | kernel-rt | Fix deferred | ||
| Red Hat Enterprise Linux 8 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 8 | kernel-rt | Fix deferred | ||
| Red Hat Enterprise Linux 9 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 9 | kernel-rt | Fix deferred | ||
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-8 | Fix deferred | ||
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-9 | Fix deferred |
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Дополнительная информация
Статус:
EPSS
5.5 Medium
CVSS3
Связанные уязвимости
In the Linux kernel, the following vulnerability has been resolved: x86/insn-eval: Fix shadowed segment index in get_seg_reg_override_idx() Commit 45e1dccc0653 ("x86/insn: Simplify for_each_insn_prefix()") made for_each_insn_prefix() declare its own loop counter named idx. get_seg_reg_override_idx() keeps its result in a local of the same name, so the assignments in the loop body now write the loop counter: - the function always returns INAT_SEG_REG_DEFAULT, so FS and GS overrides are ignored; - a CS override sets the counter to INAT_SEG_REG_CS (2), the increment makes it 3, and prefixes.bytes[3] holds the last prefix, 0x2e again, so the loop never terminates. The UMIP emulation reaches this from the #GP handler for user space: an SGDT, SIDT or SMSW with a memory operand and a CS prefix leaves the task spinning in the kernel, never returning to user space, with a SIGKILL that is never delivered. Any user can thus tie up CPUs until reboot. With an FS or GS prefix, the emulated resul...
In the Linux kernel, the following vulnerability has been resolved: x86/insn-eval: Fix shadowed segment index in get_seg_reg_override_idx() Commit 45e1dccc0653 ("x86/insn: Simplify for_each_insn_prefix()") made for_each_insn_prefix() declare its own loop counter named idx. get_seg_reg_override_idx() keeps its result in a local of the same name, so the assignments in the loop body now write the loop counter: - the function always returns INAT_SEG_REG_DEFAULT, so FS and GS overrides are ignored; - a CS override sets the counter to INAT_SEG_REG_CS (2), the increment makes it 3, and prefixes.bytes[3] holds the last prefix, 0x2e again, so the loop never terminates. The UMIP emulation reaches this from the #GP handler for user space: an SGDT, SIDT or SMSW with a memory operand and a CS prefix leaves the task spinning in the kernel, never returning to user space, with a SIGKILL that is never delivered. Any user can thus tie up CPUs until reboot. With an FS or GS prefix, the e
In the Linux kernel, the following vulnerability has been resolved: x ...
In the Linux kernel, the following vulnerability has been resolved: x86/insn-eval: Fix shadowed segment index in get_seg_reg_override_idx() Commit 45e1dccc0653 ("x86/insn: Simplify for_each_insn_prefix()") made for_each_insn_prefix() declare its own loop counter named idx. get_seg_reg_override_idx() keeps its result in a local of the same name, so the assignments in the loop body now write the loop counter: - the function always returns INAT_SEG_REG_DEFAULT, so FS and GS overrides are ignored; - a CS override sets the counter to INAT_SEG_REG_CS (2), the increment makes it 3, and prefixes.bytes[3] holds the last prefix, 0x2e again, so the loop never terminates. The UMIP emulation reaches this from the #GP handler for user space: an SGDT, SIDT or SMSW with a memory operand and a CS prefix leaves the task spinning in the kernel, never returning to user space, with a SIGKILL that is never delivered. Any user can thus tie up CPUs until reboot. With an FS or GS prefix, th...
EPSS
5.5 Medium
CVSS3