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/** @file
Random number generator services that uses RdRand instruction access
to provide high-quality random numbers.
Copyright (c) 2023, Arm Limited. All rights reserved.<BR>
Copyright (c) 2022, Pedro Falcato. All rights reserved.<BR>
Copyright (c) 2021, NUVIA Inc. All rights reserved.<BR>
Copyright (c) 2015, Intel Corporation. All rights reserved.<BR>
SPDX-License-Identifier: BSD-2-Clause-Patent
**/
#include <Uefi.h>
#include <Library/BaseLib.h>
#include <Library/BaseMemoryLib.h>
#include <Library/DebugLib.h>
#include "BaseRngLibInternals.h"
//
// Bit mask used to determine if RdRand instruction is supported.
//
#define RDRAND_MASK BIT30
STATIC BOOLEAN mRdRandSupported;
//
// Intel SDM says 10 tries is good enough for reliable RDRAND usage.
//
#define RDRAND_RETRIES 10
#define RDRAND_TEST_SAMPLES 8
#define RDRAND_MIN_CHANGE 5
//
// Add a define for native-word RDRAND, just for the test.
//
#ifdef MDE_CPU_X64
#define ASM_RDRAND AsmRdRand64
#else
#define ASM_RDRAND AsmRdRand32
#endif
/**
Tests RDRAND for broken implementations.
@retval TRUE RDRAND is reliable (and hopefully safe).
@retval FALSE RDRAND is unreliable and should be disabled, despite CPUID.
**/
STATIC
BOOLEAN
TestRdRand (
VOID
)
{
//
// Test for notoriously broken rdrand implementations that always return the same
// value, like the Zen 3 uarch (all-1s) or other several AMD families on suspend/resume (also all-1s).
// Note that this should be expanded to extensively test for other sorts of possible errata.
//
//
// Our algorithm samples rdrand $RDRAND_TEST_SAMPLES times and expects
// a different result $RDRAND_MIN_CHANGE times for reliable RDRAND usage.
//
UINTN Prev;
UINT8 Idx;
UINT8 TestIteration;
UINT32 Changed;
Changed = 0;
for (TestIteration = 0; TestIteration < RDRAND_TEST_SAMPLES; TestIteration++) {
UINTN Sample;
//
// Note: We use a retry loop for rdrand. Normal users get this in BaseRng.c
// Any failure to get a random number will assume RDRAND does not work.
//
for (Idx = 0; Idx < RDRAND_RETRIES; Idx++) {
if (ASM_RDRAND (&Sample)) {
break;
}
}
if (Idx == RDRAND_RETRIES) {
DEBUG ((DEBUG_ERROR, "BaseRngLib/x86: CPU BUG: Failed to get an RDRAND random number - disabling\n"));
return FALSE;
}
if (TestIteration != 0) {
Changed += Sample != Prev;
}
Prev = Sample;
}
if (Changed < RDRAND_MIN_CHANGE) {
DEBUG ((DEBUG_ERROR, "BaseRngLib/x86: CPU BUG: RDRAND not reliable - disabling\n"));
return FALSE;
}
return TRUE;
}
#undef ASM_RDRAND
/**
The constructor function checks whether or not RDRAND instruction is supported
by the host hardware.
The constructor function checks whether or not RDRAND instruction is supported.
It will ASSERT() if RDRAND instruction is not supported.
It will always return EFI_SUCCESS.
@retval EFI_SUCCESS The constructor always returns EFI_SUCCESS.
**/
EFI_STATUS
EFIAPI
BaseRngLibConstructor (
VOID
)
{
UINT32 RegEcx;
//
// Determine RDRAND support by examining bit 30 of the ECX register returned by
// CPUID. A value of 1 indicates that processor support RDRAND instruction.
//
AsmCpuid (1, 0, 0, &RegEcx, 0);
mRdRandSupported = ((RegEcx & RDRAND_MASK) == RDRAND_MASK);
if (mRdRandSupported) {
mRdRandSupported = TestRdRand ();
}
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
)
{
ASSERT (mRdRandSupported);
return AsmRdRand16 (Rand);
}
/**
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
)
{
ASSERT (mRdRandSupported);
return AsmRdRand32 (Rand);
}
/**
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
)
{
ASSERT (mRdRandSupported);
return AsmRdRand64 (Rand);
}
/**
Checks whether RDRAND is supported.
@retval TRUE RDRAND is supported.
@retval FALSE RDRAND is not supported.
**/
BOOLEAN
EFIAPI
ArchIsRngSupported (
VOID
)
{
return mRdRandSupported;
}
/**
Get a GUID identifying the RNG algorithm implementation.
@param [out] RngGuid If success, contains the GUID identifying
the RNG algorithm implementation.
@retval EFI_SUCCESS Success.
@retval EFI_UNSUPPORTED Not supported.
@retval EFI_INVALID_PARAMETER Invalid parameter.
**/
EFI_STATUS
EFIAPI
GetRngGuid (
GUID *RngGuid
)
{
if (RngGuid == NULL) {
return EFI_INVALID_PARAMETER;
}
CopyMem (RngGuid, &gEfiRngAlgorithmSp80090Ctr256Guid, sizeof (*RngGuid));
return EFI_SUCCESS;
}
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