x86/insn-eval: Fix shadowed segment index in get_seg_reg_override_idx()
Impact
In the Linux kernel, the following vulnerability has been resolved:
Source excerpt · LinuxAffected packages
Affected products
Vendor version evidence. Product records are separate from automatic dependency matching.
Linux · Linux
Other versions: unaffected
| Version / range | Source status |
|---|---|
| 45e1dccc0653c50e377dae57ef086a8d0f71061d to before 0efe927053f7eabd1e8658cbda96ee3d78bd1765 | affected |
| 45e1dccc0653c50e377dae57ef086a8d0f71061d to before 32c52ec87d6245ee2d12ed5dd509e40062939b50 | affected |
Linux · Linux
Other versions: affected
| Version / range | Source status |
|---|---|
| 6.19 | affected |
| 0 to before 6.19 | unaffected |
| 7.2.13 through 7.2.* (inclusive) | unaffected |
| 7.3 through * (inclusive) | unaffected |
Original source description
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:
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the function always returns INAT_SEG_REG_DEFAULT, so FS and GS overrides are ignored;
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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 ]