Preface: AMD does not plan to release any mitigations in response to this report because the reported exploit is outside the scope of the published threat model for SEV-SNP.
Remark: A physical attack is not a cyber attack because “cyber” refers to actions within computer networks and digital systems, whereas a physical attack directly involves the physical world, such as breaking into a building or destroying hardware. While a physical attack can lead to cyber vulnerabilities or data breaches, the act itself is not inherently digital.
Background: SEV-SNP is a TEE that protects the confidentiality and integrity of whole VMs against an attacker with root privileges and physical access to the machine, enabling to run SEV-protected VMs without trusting the infrastructure provider and virtualization layers such as the hypervisor.
A Trusted Execution Environment (TEE) is a secure, isolated area within a device’s main processor, protected from the main operating system and other untrusted software. It uses special hardware to create a trusted space (a “secure world”) to run sensitive code and protect data’s confidentiality and integrity. TEEs are used for security-sensitive operations like biometric authentication, secure payments, and protecting private keys in crypto wallets.
The “probe” for Serial Presence Detect (SPD) data on DDR4 and DDR5 modules is an I2C bus and associated protocols that allow the motherboard’s firmware (BIOS) to read an EEPROM chip on the memory module.
How the Attack Works?
1.Attacker gains physical access to the system and modifies the SPD data.
2.They falsely report a larger memory size than actually exists.
3.This causes the memory controller to use ghost address bits, creating aliasing — multiple physical addresses pointing to the same memory location.
4.The attacker can then:
-Overwrite encrypted guest memory.
-Inject malicious data into memory regions.
-Bypass SEV-SNP’s memory integrity protections, which assume correct physical mappings.
Official announcement: For more details, please refer to the link –
https://www.amd.com/en/resources/product-security/bulletin/amd-sb-3024.html
