CVE-2024-26603: x86/fpu: Stop relying on userspace for info to fault in xsave buffer

Vulnerability summary

CVE-2024-26603 is a medium (CVSS 5.5) Loop with Unreachable Exit Condition vulnerability in linux. EPSS estimates a 0.28% chance of exploitation in the next 30 days, higher than 20.3% of scored vulnerabilities.

Timeline

1. 24-02-2024
   PublishedVulnerability first disclosed.
2. 11-05-2026
   Last modifiedVulnerability information updated.

Description

In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Stop relying on userspace for info to fault in xsave buffer Before this change, the expected size of the user space buffer was taken from fx_sw->xstate_size. fx_sw->xstate_size can be changed from user-space, so it is possible construct a sigreturn frame where: * fx_sw->xstate_size is smaller than the size required by valid bits in fx_sw->xfeatures. * user-space unmaps parts of the sigrame fpu buffer so that not all of the buffer required by xrstor is accessible. In this case, xrstor tries to restore and accesses the unmapped area which results in a fault. But fault_in_readable succeeds because buf + fx_sw->xstate_size is within the still mapped area, so it goes back and tries xrstor again. It will spin in this loop forever. Instead, fault in the maximum size which can be touched by XRSTOR (taken from fpstate->user_size). [ dhansen: tweak subject / changelog ]

• CWE-835Loop with Unreachable Exit ConditionThe product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.