CVE-2024-35875: 
Linux Kernel vulnerability analysis and mitigation

CVE-2024-35875 addresses a security vulnerability in the Linux kernel's handling of random number generation (RNG) in Confidential Computing (CoCo) environments. The vulnerability was discovered in May 2024 and affects Linux systems utilizing CoCo features. The issue specifically relates to how the system handles RDRAND instruction failures in CoCo environments, where the VM host cannot be trusted (NVD).

The vulnerability stems from the Linux kernel's reliance on RDRAND as the only trusted source of entropy in CoCo environments. In CoCo systems, the VM host is considered untrusted and can potentially manipulate or observe most inputs to guests, making RDRAND the sole reliable source of entropy. If RDRAND fails due to CPU hardware faults, the system is designed to continue gathering entropy from other sources, but in CoCo environments, this fallback mechanism becomes catastrophic as there are no other trusted entropy sources available (Kernel Commit).

The vulnerability primarily affects boot-time security in CoCo environments. If RDRAND is broken or unavailable, it compromises the entire cryptographic security of the CoCo instance, as the system cannot establish a secure random number generation foundation. This impacts all cryptographic operations that rely on secure random number generation, potentially compromising the confidentiality and integrity of the protected environment (Kernel Commit).

The vulnerability requires either a hardware fault in the CPU's RDRAND implementation or a system booted without RDRAND support in a CoCo environment. While direct exploitation is not straightforward, the impact on cryptographic operations makes affected systems potentially vulnerable to various cryptographic attacks (NVD).

The fix implements a new security measure that requires successful RNG seeding with RDRAND on CoCo systems during boot. The system now attempts to seed the RNG using 256 bits of RDRAND output at boot time. If this fails, the system will panic rather than continue with potentially compromised entropy. This change has been implemented as a CoCo-specific driver feature rather than a core RNG modification (Kernel Commit).