3 Produced the Monotonic Counter Services as defined in the DXE CIS.
5 Copyright (c) 2006 - 2008, Intel Corporation
6 All rights reserved. This program and the accompanying materials
7 are licensed and made available under the terms and conditions of the BSD License
8 which accompanies this distribution. The full text of the license may be found at
9 http://opensource.org/licenses/bsd-license.php
11 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
12 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
17 #include "MonotonicCounter.h"
20 // The Monotonic Counter Handle
22 EFI_HANDLE mMonotonicCounterHandle
= NULL
;
25 // The current Monotonic count value
30 // Event to use to update the Mtc's high part when wrapping
32 EFI_EVENT mEfiMtcEvent
;
35 // EfiMtcName - Variable name of the MTC value
37 CHAR16
*mEfiMtcName
= (CHAR16
*) L
"MTC";
40 // EfiMtcGuid - Guid of the MTC value
42 EFI_GUID mEfiMtcGuid
= { 0xeb704011, 0x1402, 0x11d3, { 0x8e, 0x77, 0x0, 0xa0, 0xc9, 0x69, 0x72, 0x3b } };
45 Returns the low 32 bits of the platform's monotonic counter.
47 The platform's monotonic counter is comprised of two 32 bit quantities:
48 the high 32 bits and the low 32 bits.
49 During boot service time the low 32 bit value is volatile: it is reset to
50 zero on every system reset and is increased by 1 on every call to this function.
51 This function is only available at boot services time.
52 Before calling ExitBootServices() the operating system would call this function
53 to obtain the current platform monotonic count.
55 @param Count Pointer to returned value.
57 @retval EFI_INVALID_PARAMETER If Count is NULL.
58 @retval EFI_SUCCESS Operation is successful.
59 @retval EFI_UNSUPPORTED If this function is called at Runtime.
64 MonotonicCounterDriverGetNextMonotonicCount (
71 // Can not be called after ExitBootServices()
73 if (EfiAtRuntime ()) {
74 return EFI_UNSUPPORTED
;
77 // Check input parameters
80 return EFI_INVALID_PARAMETER
;
83 // Update the monotonic counter with a lock
85 OldTpl
= gBS
->RaiseTPL (TPL_HIGH_LEVEL
);
88 gBS
->RestoreTPL (OldTpl
);
91 // If the MSB bit of the low part toggled, then signal that the high
92 // part needs updated now
94 if ((((UINT32
) mEfiMtc
) ^ ((UINT32
) *Count
)) & 0x80000000) {
95 gBS
->SignalEvent (mEfiMtcEvent
);
103 Returns the next high 32 bits of the platform's monotonic counter.
105 The GetNextHighMonotonicCount() function returns the next high 32 bits
106 of the platform's monotonic counter. The platform's monotonic counter is
107 comprised of two 32 bit quantities: the high 32 bits and the low 32 bits.
108 During boot service time the low 32 bit value is volatile: it is reset to
109 zero on every system reset and is increased by 1 on every call to GetNextMonotonicCount().
110 The high 32 bit value is non-volatile and is increased by 1 whenever the system resets
111 or whenever the low 32 bit count [returned by GetNextMonoticCount()] overflows.
112 The GetNextMonotonicCount() function is only available at boot services time.
113 If the operating system wishes to extend the platform monotonic counter to runtime,
114 it may do so by utilizing GetNextHighMonotonicCount(). To do this, before calling
115 ExitBootServices() the operating system would call GetNextMonotonicCount() to obtain
116 the current platform monotonic count. The operating system would then provide an
117 interface that returns the next count by:
118 Adding 1 to the last count.
119 Before the lower 32 bits of the count overflows, call GetNextHighMonotonicCount().
120 This will increase the high 32 bits of the platform's non-volatile portion of the monotonic
123 This function may only be called at Runtime.
125 @param HighCount Pointer to returned value.
127 @retval EFI_INVALID_PARAMETER If HighCount is NULL.
128 @retval EFI_SUCCESS Operation is successful.
129 @retval EFI_OUT_OF_RESOURCES If variable service reports that not enough storage
130 is available to hold the variable and its data.
131 @retval EFI_DEVICE_ERROR The variable could not be saved due to a hardware failure.
136 MonotonicCounterDriverGetNextHighMonotonicCount (
137 OUT UINT32
*HighCount
143 // Check input parameters
145 if (HighCount
== NULL
) {
146 return EFI_INVALID_PARAMETER
;
149 if (!EfiAtRuntime ()) {
151 // Use a lock if called before ExitBootServices()
153 OldTpl
= gBS
->RaiseTPL (TPL_HIGH_LEVEL
);
154 *HighCount
= (UINT32
) RShiftU64 (mEfiMtc
, 32) + 1;
155 mEfiMtc
= LShiftU64 (*HighCount
, 32);
156 gBS
->RestoreTPL (OldTpl
);
158 *HighCount
= (UINT32
) RShiftU64 (mEfiMtc
, 32) + 1;
159 mEfiMtc
= LShiftU64 (*HighCount
, 32);
162 // Update the NvRam store to match the new high part
164 return EfiSetVariable (
167 EFI_VARIABLE_NON_VOLATILE
| EFI_VARIABLE_RUNTIME_ACCESS
| EFI_VARIABLE_BOOTSERVICE_ACCESS
,
175 Monotonic count event handler. This handler updates the high monotonic count.
177 @param Event The event to handle.
178 @param Context The event context.
192 MonotonicCounterDriverGetNextHighMonotonicCount (&HighCount
);
196 The initial function of monotonic counter driver.
198 @param ImageHandle The handle of image.
199 @param SystemTable The pointer to system table.
201 @return EFI_SUCCESS The initialize action is successful.
206 MonotonicCounterDriverInitialize (
207 IN EFI_HANDLE ImageHandle
,
208 IN EFI_SYSTEM_TABLE
*SystemTable
216 // Make sure the Monotonic Counter Architectural Protocol is not already installed in the system
218 ASSERT_PROTOCOL_ALREADY_INSTALLED (NULL
, &gEfiMonotonicCounterArchProtocolGuid
);
221 // Initialize event to handle overflows
223 Status
= gBS
->CreateEvent (
231 ASSERT_EFI_ERROR (Status
);
234 // Read the last high part
236 BufferSize
= sizeof (UINT32
);
237 Status
= EfiGetVariable (
244 if (EFI_ERROR (Status
)) {
248 // Set the current value
250 mEfiMtc
= LShiftU64 (HighCount
, 32);
253 // Increment the upper 32 bits for this boot
254 // Continue even if it fails. It will only fail if the variable services are
257 Status
= MonotonicCounterDriverGetNextHighMonotonicCount (&HighCount
);
260 // Fill in the EFI Boot Services and EFI Runtime Services Monotonic Counter Fields
262 gBS
->GetNextMonotonicCount
= MonotonicCounterDriverGetNextMonotonicCount
;
263 gRT
->GetNextHighMonotonicCount
= MonotonicCounterDriverGetNextHighMonotonicCount
;
266 // Install the Monotonic Counter Architctural Protocol onto a new handle
268 Status
= gBS
->InstallMultipleProtocolInterfaces (
269 &mMonotonicCounterHandle
,
270 &gEfiMonotonicCounterArchProtocolGuid
,
274 ASSERT_EFI_ERROR (Status
);