Bug 2281727 (CVE-2024-35875)

CVE-2024-35875 addresses a security concern in the Linux kernel's handling of confidential computing (CoCo) environments. In these setups, the virtual machine (VM) host is untrusted and may attempt to compromise guest VMs. A critical component for maintaining security in such environments is a reliable random number generator (RNG), which depends on the CPU's RDRAND instruction to generate entropy. The vulnerability arises when the RDRAND instruction fails—due to hardware faults or other issues—leaving the RNG without sufficient entropy sources. This deficiency is particularly problematic during the system's initial boot phase, potentially compromising cryptographic operations and overall system security. In CoCo environments, the untrusted VM host can manipulate or observe most inputs to guest VMs. The primary entropy source for these guests is the CPU's RDRAND instruction. If RDRAND fails, the RNG lacks alternative entropy sources, leading to potential security vulnerabilities. A malfunctioning RDRAND during boot can result in insufficient entropy for cryptographic functions, undermining the security of the CoCo environment.