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