Bug 2540299 (CVE-2026-93266)

Summary:	CVE-2026-93266 kernel: arm64: RSI: fix field-spanning write warning in attestation token init
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's ARM64 Realm Services Interface (RSI) component. When copying attestation challenge data into register structures, the kernel performs a write operation across adjacent structure fields, triggering a memory safety warning from the fortified memory copying mechanism. A local user can trigger this flaw during attestation token initialization, potentially causing a system crash and Denial of Service (DoS) on systems configured to halt on kernel warnings.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-24 16:17:59 UTC

In the Linux kernel, the following vulnerability has been resolved:

arm64: RSI: fix field-spanning write warning in attestation token init

The challenge is passed in registers a1 through a8. However, copying to
&regs.a1 makes FORTIFY treat the destination as the single a1 field,
resulting in a field-spanning write warning. [1]

Overlay the SMCCC register structure with an RSI-specific argument
layout and copy the challenge into an explicit 64-byte array. This keeps
the existing a1-a8 argument encoding while giving the copy a correctly
sized destination object.

[1]
memcpy: detected field-spanning write (size 64) of single field "&regs.a1" at ./arch/arm64/include/asm/rsi_cmds.h:119 (size 8)
WARNING: ./arch/arm64/include/asm/rsi_cmds.h:119 at rsi_attestation_token_init+0xdc/0xf8 [arm_cca_guest], CPU#0: cat/3314

Comment 1 gkamathe 2026-09-28 11:39:24 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-93266.mbox