trng.c

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// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2020 Arm Ltd.
 
#include <linux/arm-smccc.h>
#include <linux/kvm_host.h>
 
#include <asm/kvm_emulate.h>
 
#include <kvm/arm_hypercalls.h>
 
#define ARM_SMCCC_TRNG_VERSION_1_0  0x10000UL
 
/* Those values are deliberately separate from the generic SMCCC definitions. */
#define TRNG_SUCCESS            0UL
#define TRNG_NOT_SUPPORTED      ((unsigned long)-1)
#define TRNG_INVALID_PARAMETER      ((unsigned long)-2)
#define TRNG_NO_ENTROPY         ((unsigned long)-3)
 
#define TRNG_MAX_BITS64         192
 
static const uuid_t arm_smc_trng_uuid __aligned(4) = UUID_INIT(
    0x0d21e000, 0x4384, 0x11eb, 0x80, 0x70, 0x52, 0x44, 0x55, 0x4e, 0x5a, 0x4c);
 
static int kvm_trng_do_rnd(struct kvm_vcpu *vcpu, int size)
{
    DECLARE_BITMAP(bits, TRNG_MAX_BITS64);
    u32 num_bits = smccc_get_arg1(vcpu);
    int i;
 
    if (num_bits > 3 * size) {
        smccc_set_retval(vcpu, TRNG_INVALID_PARAMETER, 0, 0, 0);
        return 1;
    }
 
    /* get as many bits as we need to fulfil the request */
    for (i = 0; i < DIV_ROUND_UP(num_bits, BITS_PER_LONG); i++)
        bits[i] = get_random_long();
 
    bitmap_clear(bits, num_bits, TRNG_MAX_BITS64 - num_bits);
 
    if (size == 32)
        smccc_set_retval(vcpu, TRNG_SUCCESS, lower_32_bits(bits[1]),
                 upper_32_bits(bits[0]), lower_32_bits(bits[0]));
    else
        smccc_set_retval(vcpu, TRNG_SUCCESS, bits[2], bits[1], bits[0]);
 
    memzero_explicit(bits, sizeof(bits));
    return 1;
}
 
int kvm_trng_call(struct kvm_vcpu *vcpu)
{
    const __le32 *u = (__le32 *)arm_smc_trng_uuid.b;
    u32 func_id = smccc_get_function(vcpu);
    unsigned long val = TRNG_NOT_SUPPORTED;
    int size = 64;
 
    switch (func_id) {
    case ARM_SMCCC_TRNG_VERSION:
        val = ARM_SMCCC_TRNG_VERSION_1_0;
        break;
    case ARM_SMCCC_TRNG_FEATURES:
        switch (smccc_get_arg1(vcpu)) {
        case ARM_SMCCC_TRNG_VERSION:
        case ARM_SMCCC_TRNG_FEATURES:
        case ARM_SMCCC_TRNG_GET_UUID:
        case ARM_SMCCC_TRNG_RND32:
        case ARM_SMCCC_TRNG_RND64:
            val = TRNG_SUCCESS;
        }
        break;
    case ARM_SMCCC_TRNG_GET_UUID:
        smccc_set_retval(vcpu, le32_to_cpu(u[0]), le32_to_cpu(u[1]),
                 le32_to_cpu(u[2]), le32_to_cpu(u[3]));
        return 1;
    case ARM_SMCCC_TRNG_RND32:
        size = 32;
        fallthrough;
    case ARM_SMCCC_TRNG_RND64:
        return kvm_trng_do_rnd(vcpu, size);
    }
 
    smccc_set_retval(vcpu, val, 0, 0, 0);
    return 1;
}