This article was published on 10th Aug 2026
Official release date: August 4, 2026
Preface: AMD Zen 4 architecture is widely used in high-performance computing (HPC). It powers 4th Generation AMD EPYC server processors (such as Genoa, Genoa-X with 3D V-Cache) and the AMD Instinct MI300A accelerated processing unit (APU), which combine Zen 4 CPU cores with CDNA accelerator units for major supercomputing workloads.
Background: In the Linux kernel, arch/x86/lib/retpoline[.]S is a vital assembly file containing the system-level implementation of retpolines (return trampolines). This core security mechanic mitigates the Spectre Variant 2 vulnerability (Branch Target Injection, CVE-2017-5715) by isolating and safe-trapping speculative indirect jumps and calls on x86 architectures.
i. call [.]Ldo_rop: A direct call that hardware handles securely. It pushes the address of [.]Lspec_trap onto the CPU’s stack and hardware Return Stack Buffer (RSB).
ii. Speculative Execution Trap: The CPU attempts to guess ahead. Because of the call, the CPU’s RSB predicts that the upcoming ret instruction will jump back to [.]Lspec_trap. If the hardware executes speculatively, it gets trapped in an infinite pause; lfence; jmp loop, entirely neutralizing rogue Spectre injection.
iii. mov %rax, (%rsp): In architectural reality, the execution replaces the [.]Lspec_trap return address on the actual stack with the real intended jump destination (contained in %rax).
iv. ret: Once the CPU resolves speculation, the ret executes properly, popping the real destination out of the stack and successfully making the jump.
The Exploit Point: The attacker’s high-frequency hardware interrupt strikes precisely between step ii (mov) and step ii (ret) on the architectural side (refer to diagram). This instantly shatters the right-hand speculative trap, allowing the CPU’s branch predictor to be re-poisoned upon returning from the interrupt handler.
Vulnerability details: An external researcher has reported a potential vulnerability affecting AMD “Zen” architecture processors. The report claims that an attacker executing code on an affected system could inject an interrupt at a precise moment to disrupt “Safe RET,” the default Linux mitigation for Speculative Return Stack Overflow (SRSO), which could potentially weaken that protection and may result in information disclosure. The researcher states that this behavior was demonstrated on “Zen 1” and “Zen 2” processors and suggests that “Zen 3” and “Zen 4” could also be affected, although this has not been demonstrated.
Official announcement: Please refer to the link for details – https://www.amd.com/en/resources/product-security/bulletin/amd-sb-7061.html