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/** @file
Random number generator service that uses the SEED instruction
to provide pseudorandom numbers.
Copyright (c) 2024, Rivos, Inc.
Copyright (C) 2025 Advanced Micro Devices, Inc. All rights reserved.
SPDX-License-Identifier: BSD-2-Clause-Patent
**/
#include <Uefi.h>
#include <Library/BaseLib.h>
#include <Library/DebugLib.h>
#include <Library/RngLib.h>
#include <Register/RiscV64/RiscVEncoding.h>
#include "BaseRngLibInternals.h"
#define RISCV_CPU_FEATURE_ZKR_BITMASK 0x8
#define SEED_RETRY_LOOPS 100
// 64-bit CPU-based RNG using risc-v Zkr instruction
// Defined in Seed.S
extern UINT64
ReadSeed (
VOID
);
/**
Gets seed value by executing trng instruction (CSR 0x15) amd returns
the see to the caller 64bit value.
@param[out] Out Buffer pointer to store the 64-bit random value.
@retval TRUE Random number generated successfully.
@retval FALSE Failed to generate the random number.
**/
STATIC
BOOLEAN
Get64BitSeed (
OUT UINT64 *Out
)
{
UINT64 Seed;
UINTN Retry;
UINTN ValidSeeds;
UINTN NeededSeeds;
UINT16 *Entropy;
Retry = SEED_RETRY_LOOPS;
Entropy = (UINT16 *)Out;
NeededSeeds = sizeof (UINT64) / sizeof (UINT16);
ValidSeeds = 0;
if (!ArchIsRngSupported ()) {
DEBUG ((DEBUG_ERROR, "Get64BitSeed: HW not supported!\n"));
return FALSE;
}
do {
Seed = ReadSeed ();
switch (Seed & SEED_OPST_MASK) {
case SEED_OPST_ES16:
Entropy[ValidSeeds++] = Seed & SEED_ENTROPY_MASK;
if (ValidSeeds == NeededSeeds) {
return TRUE;
}
break;
case SEED_OPST_DEAD:
DEBUG ((DEBUG_ERROR, "Get64BitSeed: Unrecoverable error!\n"));
return FALSE;
case SEED_OPST_BIST: // fallthrough
case SEED_OPST_WAIT: // fallthrough
default:
continue;
}
} while (--Retry);
return FALSE;
}
/**
Constructor library which initializes Seeds and mStatus array.
@retval EFI_SUCCESS initialization was successful.
@retval EFI_UNSUPPORTED Feature not supported.
**/
EFI_STATUS
EFIAPI
BaseRngLibConstructor (
VOID
)
{
return EFI_SUCCESS;
}
/**
Generates a 16-bit random number.
@param[out] Rand Buffer pointer to store the 16-bit random value.
@retval TRUE Random number generated successfully.
@retval FALSE Failed to generate the random number.
**/
BOOLEAN
EFIAPI
ArchGetRandomNumber16 (
OUT UINT16 *Rand
)
{
UINT64 Rand64;
if (ArchGetRandomNumber64 (&Rand64)) {
*Rand = Rand64 & MAX_UINT16;
return TRUE;
}
return FALSE;
}
/**
Generates a 32-bit random number.
@param[out] Rand Buffer pointer to store the 32-bit random value.
@retval TRUE Random number generated successfully.
@retval FALSE Failed to generate the random number.
**/
BOOLEAN
EFIAPI
ArchGetRandomNumber32 (
OUT UINT32 *Rand
)
{
UINT64 Rand64;
if (ArchGetRandomNumber64 (&Rand64)) {
*Rand = Rand64 & MAX_UINT32;
return TRUE;
}
return FALSE;
}
/**
Generates a 64-bit random number.
@param[out] Rand Buffer pointer to store the 64-bit random value.
@retval TRUE Random number generated successfully.
@retval FALSE Failed to generate the random number.
**/
BOOLEAN
EFIAPI
ArchGetRandomNumber64 (
OUT UINT64 *Rand
)
{
UINT64 Y;
if (!Get64BitSeed (&Y)) {
return FALSE;
}
*Rand = Y;
return TRUE;
}
/**
Checks whether SEED is supported.
@retval TRUE SEED is supported.
**/
BOOLEAN
EFIAPI
ArchIsRngSupported (
VOID
)
{
return ((PcdGet64 (PcdRiscVFeatureOverride) & RISCV_CPU_FEATURE_ZKR_BITMASK) != 0);
}
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