include/vdso/getrandom.h

   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 */