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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Copyright (C) 2022-2024 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
*/
#ifndef _VDSO_GETRANDOM_H
#define _VDSO_GETRANDOM_H
#include <linux/types.h>
#define CHACHA_KEY_SIZE 32
#define CHACHA_BLOCK_SIZE 64
/**
* struct vgetrandom_state - State used by vDSO getrandom().
*
* @batch: One and a half ChaCha20 blocks of buffered RNG output.
*
* @key: Key to be used for generating next batch.
*
* @batch_key: Union of the prior two members, which is exactly two full
* ChaCha20 blocks in size, so that @batch and @key can be filled
* together.
*
* @generation: Snapshot of @rng_info->generation in the vDSO data page at
* the time @key was generated.
*
* @pos: Offset into @batch of the next available random byte.
*
* @in_use: Reentrancy guard for reusing a state within the same thread
* due to signal handlers.
*/
struct vgetrandom_state {
union {
struct {
u8 batch[CHACHA_BLOCK_SIZE * 3 / 2];
u32 key[CHACHA_KEY_SIZE / sizeof(u32)];
};
u8 batch_key[CHACHA_BLOCK_SIZE * 2];
};
u64 generation;
u8 pos;
bool in_use;
};
/**
* __arch_chacha20_blocks_nostack - Generate ChaCha20 stream without using the stack.
* @dst_bytes: Destination buffer to hold @nblocks * 64 bytes of output.
* @key: 32-byte input key.
* @counter: 8-byte counter, read on input and updated on return.
* @nblocks: Number of blocks to generate.
*
* Generates a given positive number of blocks of ChaCha20 output with nonce=0, and does not write
* to any stack or memory outside of the parameters passed to it, in order to mitigate stack data
* leaking into forked child processes.
*/
extern void __arch_chacha20_blocks_nostack(u8 *dst_bytes, const u32 *key, u32 *counter, size_t nblocks);
/**
* __vdso_getrandom - Architecture-specific vDSO implementation of getrandom() syscall.
* @buffer: Passed to __cvdso_getrandom().
* @len: Passed to __cvdso_getrandom().
* @flags: Passed to __cvdso_getrandom().
* @opaque_state: Passed to __cvdso_getrandom().
* @opaque_len: Passed to __cvdso_getrandom();
*
* This function is implemented by making a single call to to __cvdso_getrandom(), whose
* documentation may be consulted for more information.
*
* Returns: The return value of __cvdso_getrandom().
*/
extern ssize_t __vdso_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state, size_t opaque_len);
#endif /* _VDSO_GETRANDOM_H */
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