mirror of
https://github.com/CloverHackyColor/CloverBootloader.git
synced 2024-11-24 11:45:27 +01:00
96 lines
2.9 KiB
C
96 lines
2.9 KiB
C
/** @file
|
|
Copyright (C) 2019, Download-Fritz. All rights reserved.
|
|
|
|
This program and the accompanying materials
|
|
are licensed and made available under the terms and conditions of the BSD License
|
|
which accompanies this distribution. The full text of the license may be found at
|
|
http://opensource.org/licenses/bsd-license.php
|
|
|
|
THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
|
|
WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
|
|
|
|
**/
|
|
|
|
#include <Base.h>
|
|
|
|
#include <Library/DebugLib.h>
|
|
|
|
INTN
|
|
SecureCompareMem (
|
|
IN CONST VOID *DestinationBuffer,
|
|
IN CONST VOID *SourceBuffer,
|
|
IN UINTN Length
|
|
)
|
|
{
|
|
//
|
|
// Based on libsodium secure_memcmp function implementation.
|
|
//
|
|
UINTN Index;
|
|
//
|
|
// The loop variables are volatile to prevent compiler optimizations, such as
|
|
// security-hurting simplifications and intrinsics insertion.
|
|
//
|
|
volatile CONST UINT8 *volatile Destination;
|
|
volatile CONST UINT8 *volatile Source;
|
|
volatile UINT8 XorDiff;
|
|
|
|
if (Length > 0) {
|
|
ASSERT (DestinationBuffer != NULL);
|
|
ASSERT (SourceBuffer != NULL);
|
|
ASSERT ((Length - 1) <= (MAX_ADDRESS - (UINTN) DestinationBuffer));
|
|
ASSERT ((Length - 1) <= (MAX_ADDRESS - (UINTN) SourceBuffer));
|
|
}
|
|
|
|
Destination = (volatile CONST UINT8 *) DestinationBuffer;
|
|
Source = (volatile CONST UINT8 *) SourceBuffer;
|
|
|
|
XorDiff = 0;
|
|
for (Index = 0; Index < Length; ++Index) {
|
|
//
|
|
// XOR is used to prevent comparison result based branches causing
|
|
// slightly different execution times. A XOR operation only yields 0 when
|
|
// both operands are equal.
|
|
// Do not break early on mismatch to not leak information about prefixes.
|
|
// The AND operation with 0xFFU is performed to have a result promotion to
|
|
// unsigned int rather than int to ensure a safe cast.
|
|
//
|
|
XorDiff |= (UINT8)((Destination[Index] ^ (Source[Index])) & 0xFFU);
|
|
}
|
|
//
|
|
// This is implemented as an arithmetic operation to have an uniform
|
|
// execution time for success and failure cases.
|
|
//
|
|
// For XorDiff = 0, the subtraction wraps around and leads to a value of
|
|
// UINT_MAX. All other values, as XorDiff is unsigned, must be greater than 0
|
|
// and hence cannot wrap around. This means extracting bit 8 of the
|
|
// operation's result will always yield 1 for XorDiff = 0 and always yield 0
|
|
// for XorDiff != 0. This is then cast to INTN, which is safe because it
|
|
// can only ever be 0 or 1, to finally yield the appropiate return value.
|
|
//
|
|
return ((INTN)(1U & ((XorDiff - 1U) >> 8U))) - 1;
|
|
}
|
|
|
|
VOID *
|
|
SecureZeroMem (
|
|
OUT VOID *Buffer,
|
|
IN UINTN Length
|
|
)
|
|
{
|
|
volatile UINT8 *Destination;
|
|
|
|
if (Length == 0) {
|
|
return Buffer;
|
|
}
|
|
|
|
ASSERT (Buffer != NULL);
|
|
ASSERT (Length <= (MAX_ADDRESS - (UINTN) Buffer + 1));
|
|
|
|
Destination = (volatile UINT8 *) Buffer;
|
|
|
|
while (Length--) {
|
|
*Destination++ = 0;
|
|
}
|
|
|
|
return Buffer;
|
|
}
|