Bug 2554978 (CVE-2026-98551)

Summary:	CVE-2026-98551 kernel: perf/core: Fill branch entries with a single assignment
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
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 Performance Events (perf) subsystem on ARM64 architectures. This flaw allows a local user to cause an information disclosure of sensitive kernel memory. The issue occurs because certain branch tracking data structures are not properly cleared, allowing an attacker reading branch records to access uninitialized kernel memory.	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 2026-10-18 15:37:03 UTC

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

perf/core: Fill branch entries with a single assignment

perf_clear_branch_entry_bitfields() clears the bitfields of struct
perf_branch_entry one by one and leaves from/to alone, since callers
overwrite those straight away. The list has to be kept in sync with the
struct by hand and has already fallen behind: new_type and priv were
added to perf_branch_entry and never added here.

Only BRBE writes those two, and neither for every record.
brbe_set_perf_entry_type() leaves new_type alone for a branch type it
does not recognise, and priv is not set for source-only records.
arm_pmuv3.c allocates the per-CPU branch stack with kmalloc(), so such a
record reaches userspace with whatever the slot held: uninitialised
kmalloc() data on the first pass over the buffer, the previous record's
values after that. Nothing under arch/x86/events/ writes either field,
so only arm64 is affected.

Assign the whole entry at each site instead. Everything not named is
then zero, and there is no list to keep in sync. The bitfields add up to
exactly 64 bits, so the struct has no padding to leave undefined.

perf_clear_branch_entry_bitfields() has no callers left, so remove it.
perf_entry_from_brbe_regset() assigns an empty literal instead, since it
fills from/to conditionally. PERF_BR_SPEC_NA is 0, so dropping the
explicit spec assignment changes nothing.