CVE-2023-20588

When a division faults for dividing by zero, Zen 1 processors can return speculative data to the instructions after it. AMD’s advice is to keep privileged data out of divisions before a change of privilege. AMD rates it low: the data may not be privileged and the attacker does not control which division produced it, and it believes processors from Zen 2 on are not affected. Linux treats every Zen 1 processor, Zen+ included, as affected and asks for SMT to be turned off for full protection.

Affected processors

2 of the 2 microarchitectures listed are affected in all or some of their models.

Microarchitecture	Status	Detail	Source
Zen	Affected	Linux 7.3 treats family 17h models 00h-2Fh and 50h-5Fh as Zen 1	Linux 7.3
Zen+	Affected	Linux 7.3 treats family 17h models 00h-2Fh and 50h-5Fh, Zen+ among them, as Zen 1	Linux 7.3

Mitigations

• Programs: No privileged data in division operations before a change of privilege, so a later faulting division cannot return it. Instructions: DIV. Source.
• Kernel: Linux 7.3 marks Zen 1 processors with the bug div0 and asks for SMT to be disabled for full protection. Source.