Another try for getrandom() in the vDSO

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2024-07-05 12:30:38

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By Jonathan Corbet July 4, 2024 Random numbers, it seems, can never be random enough, and they cannot be generated quickly enough. The kernel's getrandom() system call might, after years of discussion, be seen as sufficiently secure by most users, but it is still a system call. Linux system calls are relatively fast, but they are necessarily slower than calling a function directly. In an attempt to speed the provision of secure random data to user space, Jason Donenfeld has put together an implementation of getrandom() that lives in the virtual dynamic shared object (vDSO) area.

Random data is used in no end of applications, including modeling of natural phenomena, generation of identifiers like UUIDs, and game play; it's how NetHack somehow summons those three balrogs all in one corner of a dark room. Security-related operations, such as the generation of nonces and keys, also make heavy use of random data — and depend heavily on that data actually being random. Some applications need so much random data that they spend a significant amount of time in the getrandom() system call.