Bug 2323929 (CVE-2024-50102)

Summary:	CVE-2024-50102 kernel: x86: fix user address masking non-canonical speculation issue
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:	dfreiber, drow, jburrell, rhel-process-autobot, vkumar, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
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Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:	A flaw was found in the Linux kernel's handling of user address masking on x86 architectures. This vulnerability, similar to "Meltdown Lite," allows for speculative execution (a CPU optimization technique) to be exploited due to incorrect handling of non-canonical memory accesses in kernel space. A local attacker with low privileges could leverage this issue to potentially leak sensitive data from kernel memory. This affects AMD Zen 5 and newer processors, where the speculation window remains open.	Story Points:	---
Clone Of:		Environment:
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Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2324029
Bug Blocks:

Description OSIDB Bzimport 2024-11-05 18:02:49 UTC

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

x86: fix user address masking non-canonical speculation issue

It turns out that AMD has a "Meltdown Lite(tm)" issue with non-canonical
accesses in kernel space.  And so using just the high bit to decide
whether an access is in user space or kernel space ends up with the good
old "leak speculative data" if you have the right gadget using the
result:

  CVE-2020-12965 “Transient Execution of Non-Canonical Accesses“

Now, the kernel surrounds the access with a STAC/CLAC pair, and those
instructions end up serializing execution on older Zen architectures,
which closes the speculation window.

But that was true only up until Zen 5, which renames the AC bit [1].
That improves performance of STAC/CLAC a lot, but also means that the
speculation window is now open.

Note that this affects not just the new address masking, but also the
regular valid_user_address() check used by access_ok(), and the asm
version of the sign bit check in the get_user() helpers.

It does not affect put_user() or clear_user() variants, since there's no
speculative result to be used in a gadget for those operations.

Comment 1 Robb Gatica 2024-11-05 21:13:22 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2024110553-CVE-2024-50102-3d1e@gregkh/T

Comment 2 errata-xmlrpc 2025-05-13 08:32:35 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9

Via RHSA-2025:6966 https://access.redhat.com/errata/RHSA-2025:6966

Comment 3 errata-xmlrpc 2025-09-11 06:36:01 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.4 Extended Update Support

Via RHSA-2025:15668 https://access.redhat.com/errata/RHSA-2025:15668