MdePkg/Library/BaseLib/X86Thunk.c

   1 /** @file
   2   Real Mode Thunk Functions for IA32 and x64.
   3
   4   Copyright (c) 2006 - 2018, Intel Corporation. All rights reserved.<BR>
   5   SPDX-License-Identifier: BSD-2-Clause-Patent
   6
   7 **/
   8
   9
  10 #include "BaseLibInternals.h"
  11
  12 extern CONST UINT8                  m16Start;
  13 extern CONST UINT16                 m16Size;
  14 extern CONST UINT16                 mThunk16Attr;
  15 extern CONST UINT16                 m16Gdt;
  16 extern CONST UINT16                 m16GdtrBase;
  17 extern CONST UINT16                 mTransition;
  18
  19 /**
  20   Invokes 16-bit code in big real mode and returns the updated register set.
  21
  22   This function transfers control to the 16-bit code specified by CS:EIP using
  23   the stack specified by SS:ESP in RegisterSet. The updated registers are saved
  24   on the real mode stack and the starting address of the save area is returned.
  25
  26   @param  RegisterSet Values of registers before invocation of 16-bit code.
  27   @param  Transition  The pointer to the transition code under 1MB.
  28
  29   @return The pointer to a IA32_REGISTER_SET structure containing the updated
  30           register values.
  31
  32 **/
  33 IA32_REGISTER_SET *
  34 EFIAPI
  35 InternalAsmThunk16 (
  36   IN      IA32_REGISTER_SET         *RegisterSet,
  37   IN OUT  VOID                      *Transition
  38   );
  39
  40 /**
  41   Retrieves the properties for 16-bit thunk functions.
  42
  43   Computes the size of the buffer and stack below 1MB required to use the
  44   AsmPrepareThunk16(), AsmThunk16() and AsmPrepareAndThunk16() functions. This
  45   buffer size is returned in RealModeBufferSize, and the stack size is returned
  46   in ExtraStackSize. If parameters are passed to the 16-bit real mode code,
  47   then the actual minimum stack size is ExtraStackSize plus the maximum number
  48   of bytes that need to be passed to the 16-bit real mode code.
  49
  50   If RealModeBufferSize is NULL, then ASSERT().
  51   If ExtraStackSize is NULL, then ASSERT().
  52
  53   @param  RealModeBufferSize  A pointer to the size of the buffer below 1MB
  54                               required to use the 16-bit thunk functions.
  55   @param  ExtraStackSize      A pointer to the extra size of stack below 1MB
  56                               that the 16-bit thunk functions require for
  57                               temporary storage in the transition to and from
  58                               16-bit real mode.
  59
  60 **/
  61 VOID
  62 EFIAPI
  63 AsmGetThunk16Properties (
  64   OUT     UINT32                    *RealModeBufferSize,
  65   OUT     UINT32                    *ExtraStackSize
  66   )
  67 {
  68   ASSERT (RealModeBufferSize != NULL);
  69   ASSERT (ExtraStackSize != NULL);
  70
  71   *RealModeBufferSize = m16Size;
  72
  73   //
  74   // Extra 4 bytes for return address, and another 4 bytes for mode transition
  75   //
  76   *ExtraStackSize = sizeof (IA32_DWORD_REGS) + 8;
  77 }
  78
  79 /**
  80   Prepares all structures a code required to use AsmThunk16().
  81
  82   Prepares all structures and code required to use AsmThunk16().
  83
  84   This interface is limited to be used in either physical mode or virtual modes with paging enabled where the
  85   virtual to physical mappings for ThunkContext.RealModeBuffer is mapped 1:1.
  86
  87   If ThunkContext is NULL, then ASSERT().
  88
  89   @param  ThunkContext  A pointer to the context structure that describes the
  90                         16-bit real mode code to call.
  91
  92 **/
  93 VOID
  94 EFIAPI
  95 AsmPrepareThunk16 (
  96   IN OUT  THUNK_CONTEXT             *ThunkContext
  97   )
  98 {
  99   IA32_SEGMENT_DESCRIPTOR           *RealModeGdt;
 100
 101   ASSERT (ThunkContext != NULL);
 102   ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
 103   ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
 104   ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
 105
 106   CopyMem (ThunkContext->RealModeBuffer, &m16Start, m16Size);
 107
 108   //
 109   // Point RealModeGdt to the GDT to be used in transition
 110   //
 111   // RealModeGdt[0]: Reserved as NULL descriptor
 112   // RealModeGdt[1]: Code Segment
 113   // RealModeGdt[2]: Data Segment
 114   // RealModeGdt[3]: Call Gate
 115   //
 116   RealModeGdt = (IA32_SEGMENT_DESCRIPTOR*)(
 117                   (UINTN)ThunkContext->RealModeBuffer + m16Gdt);
 118
 119   //
 120   // Update Code & Data Segment Descriptor
 121   //
 122   RealModeGdt[1].Bits.BaseLow =
 123     (UINT32)(UINTN)ThunkContext->RealModeBuffer & ~0xf;
 124   RealModeGdt[1].Bits.BaseMid =
 125     (UINT32)(UINTN)ThunkContext->RealModeBuffer >> 16;
 126
 127   //
 128   // Update transition code entry point offset
 129   //
 130   *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mTransition) +=
 131     (UINT32)(UINTN)ThunkContext->RealModeBuffer & 0xf;
 132
 133   //
 134   // Update Segment Limits for both Code and Data Segment Descriptors
 135   //
 136   if ((ThunkContext->ThunkAttributes & THUNK_ATTRIBUTE_BIG_REAL_MODE) == 0) {
 137     //
 138     // Set segment limits to 64KB
 139     //
 140     RealModeGdt[1].Bits.LimitHigh = 0;
 141     RealModeGdt[1].Bits.G = 0;
 142     RealModeGdt[2].Bits.LimitHigh = 0;
 143     RealModeGdt[2].Bits.G = 0;
 144   }
 145
 146   //
 147   // Update GDTBASE for this thunk context
 148   //
 149   *(VOID**)((UINTN)ThunkContext->RealModeBuffer + m16GdtrBase) = RealModeGdt;
 150
 151   //
 152   // Update Thunk Attributes
 153   //
 154   *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mThunk16Attr) =
 155     ThunkContext->ThunkAttributes;
 156 }
 157
 158 /**
 159   Transfers control to a 16-bit real mode entry point and returns the results.
 160
 161   Transfers control to a 16-bit real mode entry point and returns the results.
 162   AsmPrepareThunk16() must be called with ThunkContext before this function is used.
 163   This function must be called with interrupts disabled.
 164
 165   The register state from the RealModeState field of ThunkContext is restored just prior
 166   to calling the 16-bit real mode entry point.  This includes the EFLAGS field of RealModeState,
 167   which is used to set the interrupt state when a 16-bit real mode entry point is called.
 168   Control is transferred to the 16-bit real mode entry point specified by the CS and Eip fields of RealModeState.
 169   The stack is initialized to the SS and ESP fields of RealModeState.  Any parameters passed to
 170   the 16-bit real mode code must be populated by the caller at SS:ESP prior to calling this function.
 171   The 16-bit real mode entry point is invoked with a 16-bit CALL FAR instruction,
 172   so when accessing stack contents, the 16-bit real mode code must account for the 16-bit segment
 173   and 16-bit offset of the return address that were pushed onto the stack. The 16-bit real mode entry
 174   point must exit with a RETF instruction. The register state is captured into RealModeState immediately
 175   after the RETF instruction is executed.
 176
 177   If EFLAGS specifies interrupts enabled, or any of the 16-bit real mode code enables interrupts,
 178   or any of the 16-bit real mode code makes a SW interrupt, then the caller is responsible for making sure
 179   the IDT at address 0 is initialized to handle any HW or SW interrupts that may occur while in 16-bit real mode.
 180
 181   If EFLAGS specifies interrupts enabled, or any of the 16-bit real mode code enables interrupts,
 182   then the caller is responsible for making sure the 8259 PIC is in a state compatible with 16-bit real mode.
 183   This includes the base vectors, the interrupt masks, and the edge/level trigger mode.
 184
 185   If THUNK_ATTRIBUTE_BIG_REAL_MODE is set in the ThunkAttributes field of ThunkContext, then the user code
 186   is invoked in big real mode.  Otherwise, the user code is invoked in 16-bit real mode with 64KB segment limits.
 187
 188   If neither THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 nor THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL are set in
 189   ThunkAttributes, then it is assumed that the user code did not enable the A20 mask, and no attempt is made to
 190   disable the A20 mask.
 191
 192   If THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 is set and THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL is clear in
 193   ThunkAttributes, then attempt to use the INT 15 service to disable the A20 mask.  If this INT 15 call fails,
 194   then attempt to disable the A20 mask by directly accessing the 8042 keyboard controller I/O ports.
 195
 196   If THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 is clear and THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL is set in
 197   ThunkAttributes, then attempt to disable the A20 mask by directly accessing the 8042 keyboard controller I/O ports.
 198
 199   If ThunkContext is NULL, then ASSERT().
 200   If AsmPrepareThunk16() was not previously called with ThunkContext, then ASSERT().
 201   If both THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 and THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL are set in
 202   ThunkAttributes, then ASSERT().
 203
 204   This interface is limited to be used in either physical mode or virtual modes with paging enabled where the
 205   virtual to physical mappings for ThunkContext.RealModeBuffer is mapped 1:1.
 206
 207   @param  ThunkContext  A pointer to the context structure that describes the
 208                         16-bit real mode code to call.
 209
 210 **/
 211 VOID
 212 EFIAPI
 213 AsmThunk16 (
 214   IN OUT  THUNK_CONTEXT             *ThunkContext
 215   )
 216 {
 217   IA32_REGISTER_SET                 *UpdatedRegs;
 218
 219   ASSERT (ThunkContext != NULL);
 220   ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
 221   ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
 222   ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
 223   ASSERT (((ThunkContext->ThunkAttributes & (THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 | THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL)) != \
 224            (THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 | THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL)));
 225
 226   UpdatedRegs = InternalAsmThunk16 (
 227                   ThunkContext->RealModeState,
 228                   ThunkContext->RealModeBuffer
 229                   );
 230
 231   CopyMem (ThunkContext->RealModeState, UpdatedRegs, sizeof (*UpdatedRegs));
 232 }
 233
 234 /**
 235   Prepares all structures and code for a 16-bit real mode thunk, transfers
 236   control to a 16-bit real mode entry point, and returns the results.
 237
 238   Prepares all structures and code for a 16-bit real mode thunk, transfers
 239   control to a 16-bit real mode entry point, and returns the results. If the
 240   caller only need to perform a single 16-bit real mode thunk, then this
 241   service should be used. If the caller intends to make more than one 16-bit
 242   real mode thunk, then it is more efficient if AsmPrepareThunk16() is called
 243   once and AsmThunk16() can be called for each 16-bit real mode thunk.
 244
 245   This interface is limited to be used in either physical mode or virtual modes with paging enabled where the
 246   virtual to physical mappings for ThunkContext.RealModeBuffer is mapped 1:1.
 247
 248   See AsmPrepareThunk16() and AsmThunk16() for the detailed description and ASSERT() conditions.
 249
 250   @param  ThunkContext  A pointer to the context structure that describes the
 251                         16-bit real mode code to call.
 252
 253 **/
 254 VOID
 255 EFIAPI
 256 AsmPrepareAndThunk16 (
 257   IN OUT  THUNK_CONTEXT             *ThunkContext
 258   )
 259 {
 260   AsmPrepareThunk16 (ThunkContext);
 261   AsmThunk16 (ThunkContext);
 262 }