/* 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 */