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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 */
33struct 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 */
57extern 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 */
72extern 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

source code of linux/include/vdso/getrandom.h