Bug 2348908 (CVE-2025-21818)

Summary: CVE-2025-21818 kernel: x86/xen: fix xen_hypercall_hvm() to not clobber %rbx
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: unspecifiedCC: dfreiber, drow, jburrell, vkumar
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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[REJECTED CVE] In the Linux kernel, the following vulnerability has been resolved: x86/xen: fix xen_hypercall_hvm() to not clobber %rbx xen_hypercall_hvm(), which is used when running as a Xen PVH guest at most only once during early boot, is clobbering %rbx. Depending on whether the caller relies on %rbx to be preserved across the call or not, this clobbering might result in an early crash of the system.
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Description OSIDB Bzimport 2025-02-27 21:02:46 UTC 
In the Linux kernel, the following vulnerability has been resolved:

x86/xen: fix xen_hypercall_hvm() to not clobber %rbx

xen_hypercall_hvm(), which is used when running as a Xen PVH guest at
most only once during early boot, is clobbering %rbx. Depending on
whether the caller relies on %rbx to be preserved across the call or
not, this clobbering might result in an early crash of the system.

This can be avoided by using an already saved register instead of %rbx.
Comment 1 Avinash Hanwate 2025-02-28 04:52:34 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025022710-CVE-2025-21818-27ee@gregkh/T
Comment 2 TEJ RATHI 2025-05-15 08:05:39 UTC 
This CVE has been rejected upstream: https://lore.kernel.org/linux-cve-announce/2025030232-REJECTED-daed@gregkh/