CVE-2024-56761 Information

Description

In the Linux kernel the following vulnerability has been resolved:

x86/fred: Clear WFE in missing-ENDBRANCH CPs

An indirect branch instruction sets the CPU indirect branch tracker (IBT) into WAIT_FOR_ENDBRANCH (WFE) state and WFE stays asserted across the instruction boundary. When the decoder finds an inappropriate instruction while WFE is set ENDBR the CPU raises a CP fault.

For the \kernel IBT no ENDBR\ selftest where CPs are deliberately triggered the WFE state of the interrupted context needs to be cleared to let execution continue. Otherwise when the CPU resumes from the instruction that just caused the previous CP another missing-ENDBRANCH CP is raised and the CPU enters a dead loop.

This is not a problem with IDT because it doesn’t preserve WFE and IRET doesn’t set WFE. But FRED provides space on the entry stack (in an expanded CS area) to save and restore the WFE state thus the WFE state is no longer clobbered so software must clear it.

Clear WFE to avoid dead looping in ibt_clear_fred_wfe() and the !ibt_fatal code path when execution is allowed to continue.

Clobbering WFE in any other circumstance is a security-relevant bug.

[ dhansen: changelog rewording ]

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Reference

https://git.kernel.org/stable/c/b939f108e86b76119428a6fa4e92491e09ac7867 https://git.kernel.org/stable/c/dc81e556f2a017d681251ace21bf06c126d5a192

Attack Complexity

LOW

Privileges Required

LOW

User Interaction Required

LOW

Scope

NONE

Confidentiality Impact

UNCHANGED

Integrity Impact

NONE

Availability Impact

NONE

Base Score

HIGH

Base Severity

5.5