1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* 3 * Copyright (C) 2022-2024 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. 4 */ 5 6 #ifndef _VDSO_GETRANDOM_H 7 #define _VDSO_GETRANDOM_H 8 9 #include <linux/types.h> 10 11 #define CHACHA_KEY_SIZE 32 12 #define CHACHA_BLOCK_SIZE 64 13 14 /** 15 * struct vgetrandom_state - State used by vDSO getrandom(). 16 * 17 * @batch: One and a half ChaCha20 blocks of buffered RNG output. 18 * 19 * @key: Key to be used for generating next batch. 20 * 21 * @batch_key: Union of the prior two members, which is exactly two full 22 * ChaCha20 blocks in size, so that @batch and @key can be filled 23 * together. 24 * 25 * @generation: Snapshot of @rng_info->generation in the vDSO data page at 26 * the time @key was generated. 27 * 28 * @pos: Offset into @batch of the next available random byte. 29 * 30 * @in_use: Reentrancy guard for reusing a state within the same thread 31 * due to signal handlers. 32 */ 33 struct vgetrandom_state { 34 union { 35 struct { 36 u8 batch[CHACHA_BLOCK_SIZE * 3 / 2]; 37 u32 key[CHACHA_KEY_SIZE / sizeof(u32)]; 38 }; 39 u8 batch_key[CHACHA_BLOCK_SIZE * 2]; 40 }; 41 u64 generation; 42 u8 pos; 43 bool in_use; 44 }; 45 46 /** 47 * __arch_chacha20_blocks_nostack - Generate ChaCha20 stream without using the stack. 48 * @dst_bytes: Destination buffer to hold @nblocks * 64 bytes of output. 49 * @key: 32-byte input key. 50 * @counter: 8-byte counter, read on input and updated on return. 51 * @nblocks: Number of blocks to generate. 52 * 53 * Generates a given positive number of blocks of ChaCha20 output with nonce=0, and does not write 54 * to any stack or memory outside of the parameters passed to it, in order to mitigate stack data 55 * leaking into forked child processes. 56 */ 57 extern void __arch_chacha20_blocks_nostack(u8 *dst_bytes, const u32 *key, u32 *counter, size_t nblocks); 58 59 /** 60 * __vdso_getrandom - Architecture-specific vDSO implementation of getrandom() syscall. 61 * @buffer: Passed to __cvdso_getrandom(). 62 * @len: Passed to __cvdso_getrandom(). 63 * @flags: Passed to __cvdso_getrandom(). 64 * @opaque_state: Passed to __cvdso_getrandom(). 65 * @opaque_len: Passed to __cvdso_getrandom(); 66 * 67 * This function is implemented by making a single call to to __cvdso_getrandom(), whose 68 * documentation may be consulted for more information. 69 * 70 * Returns: The return value of __cvdso_getrandom(). 71 */ 72 extern ssize_t __vdso_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state, size_t opaque_len); 73 74 #endif /* _VDSO_GETRANDOM_H */ 75