647 lines
19 KiB
NASM
647 lines
19 KiB
NASM
;------------------------------------------------------------------------------
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;
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; Some assembler helper functions plus boot.efi kernel jump callback
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;
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; by dmazar
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;
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;------------------------------------------------------------------------------
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XDTR STRUCT
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Limit DW ?
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Base DQ ?
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XDTR ENDS
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; C callback method called on jump to kernel after boot.efi finishes
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EXTERN KernelEntryPatchJumpBack:PROC
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; saved 64bit state
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PUBLIC SavedCR3
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PUBLIC SavedGDTR
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PUBLIC SavedIDTR
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; addresses of relocated MyAsmCopyAndJumpToKernel code - filled by PrepareJumpFromKernel()
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PUBLIC MyAsmCopyAndJumpToKernel32Addr
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PUBLIC MyAsmCopyAndJumpToKernel64Addr
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; kernel entry address - filled by KernelEntryPatchJump()
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PUBLIC AsmKernelEntry
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; params for kernel image relocation - filled by KernelEntryPatchJumpBack()
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PUBLIC AsmKernelImageStartReloc
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PUBLIC AsmKernelImageStart
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PUBLIC AsmKernelImageSize
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; end of MyAsmEntryPatchCode func
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PUBLIC MyAsmEntryPatchCodeEnd
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; start and end of MyAsmCopyAndJumpToKernel
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PUBLIC MyAsmCopyAndJumpToKernel
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PUBLIC MyAsmCopyAndJumpToKernel32
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PUBLIC MyAsmCopyAndJumpToKernel64
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PUBLIC MyAsmCopyAndJumpToKernelEnd
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.data
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; variables accessed from both 32 and 64 bit code
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; need to have this exactly in this order
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DataBase:
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; 64 bit state
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SavedGDTROff EQU $-DataBase
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SavedGDTR XDTR <?>
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SavedIDTROff EQU $-DataBase
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SavedIDTR XDTR <?>
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align 08h
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SavedCR3Off EQU $-DataBase
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SavedCR3 DQ ?
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SavedCSOff EQU $-DataBase
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SavedCS DW ?
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SavedDSOff EQU $-DataBase
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SavedDS DW ?
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; 32 bit state
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SavedGDTR32Off EQU $-DataBase
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SavedGDTR32 XDTR <?>
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SavedIDTR32Off EQU $-DataBase
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SavedIDTR32 XDTR <?>
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SavedCS32Off EQU $-DataBase
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SavedCS32 DW ?
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SavedDS32Off EQU $-DataBase
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SavedDS32 DW ?
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SavedESP32Off EQU $-DataBase
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SavedESP32 DD ?
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align 08h
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; address of relocated MyAsmCopyAndJumpToKernel32 - 64 bit
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MyAsmCopyAndJumpToKernel32AddrOff EQU $-DataBase
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MyAsmCopyAndJumpToKernel32Addr DQ 0
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; address of relocated MyAsmCopyAndJumpToKernel64 - 64 bit
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MyAsmCopyAndJumpToKernel64AddrOff EQU $-DataBase
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MyAsmCopyAndJumpToKernel64Addr DQ 0
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; kernel entry - 64 bit
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AsmKernelEntryOff EQU $-DataBase
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AsmKernelEntry DQ 0
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;
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; for copying kernel image from reloc block to proper mem place
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;
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; kernel image start in reloc block (source) - 64 bit
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AsmKernelImageStartRelocOff EQU $-DataBase
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AsmKernelImageStartReloc DQ 0
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; kernel image start (destination) - 64 bit
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AsmKernelImageStartOff EQU $-DataBase
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AsmKernelImageStart DQ 0
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; kernel image size - 64 bit
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AsmKernelImageSizeOff EQU $-DataBase
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AsmKernelImageSize DQ 0
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align 08h
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; GDT not used since we are reusing UEFI state
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; but left here in case will be needed.
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;
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; GDR record
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GDTROff EQU $-DataBase
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GDTR dw GDT_END - GDT_BASE - 1 ; GDT limit
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GDTR_BASE dq 0 ; GDT base - needs to be set in code
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align 08h
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; GDT
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GDT_BASE:
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; null descriptor
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NULL_SEL equ $-GDT_BASE ; 0x00
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dw 0 ; limit 15:0
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dw 0 ; base 15:0
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db 0 ; base 23:16
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db 0 ; type
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db 0 ; limit 19:16, flags
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db 0 ; base 31:24
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; 64 bit code segment descriptor
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CODE64_SEL equ $-GDT_BASE ; 0x08
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dw 0FFFFh ; limit 0xFFFFF
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dw 0 ; base 0
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db 0
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db 09Ah ; P=1 | DPL=00 | S=1 (User) # Type=A=1010: Code/Data=1 | C:Conforming=0 | R:Readable=1 | A:Accessed=0
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db 0AFh ; Flags=A=1010: G:Granularity=1 (4K) | D:Default Operand Size=0 (in long mode) | L:Long=1 (64 bit) | AVL=0
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db 0
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; 32 bit and 64 bit data segment descriptor (in 64 bit almost all is ignored, so can be reused)
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DATA_SEL equ $-GDT_BASE ; 0x10
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dw 0FFFFh ; limit 0xFFFFF
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dw 0 ; base 0
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db 0
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db 092h ; P=1 | DPL=00 | S=1 (User) # Type=2=0010: Code/Data=0 | E:Expand-Down=0 | W:Writable=1 | A:Accessed=0
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db 0CFh ; Flags=C=1100: G:Granularity=1 (4K) | D/B=1 D not used when E=0, for stack B=1 means 32 bit stack | L:Long=0 not used | AVL=0
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db 0
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; 32 bit code segment descriptor
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CODE32_SEL equ $-GDT_BASE ; 0x18
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dw 0FFFFh ; limit 0xFFFFF
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dw 0 ; base 0
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db 0
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db 09Ah ; P=1 | DPL=00 | S=1 (User) # Type=A=1010: Code/Data=1 | C:Conforming=0 | R:Readable=1 | A:Accessed=0
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db 0CFh ; Flags=C=1100: G:Granularity=1 (4K) | D:Default Operand Size=0 (in long mode) | L:Long=0 (32 bit) | AVL=0
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db 0
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GDT_END:
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.code
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;------------------------------------------------------------------------------
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; UINT64
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; EFIAPI
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; MyAsmReadSp (
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; VOID
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; );
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;------------------------------------------------------------------------------
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MyAsmReadSp PROC
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mov rax, rsp
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add rax, 8 ; return SP as caller see it
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ret
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MyAsmReadSp ENDP
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;------------------------------------------------------------------------------
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; VOID
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; EFIAPI
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; MyAsmPrepareJumpFromKernel (
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; );
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;------------------------------------------------------------------------------
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MyAsmPrepareJumpFromKernel PROC
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; save 64 bit state
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sgdt SavedGDTR
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sidt SavedIDTR
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mov rax, cr3
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mov QWORD PTR SavedCR3, rax
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mov WORD PTR SavedCS, cs
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mov WORD PTR SavedDS, ds
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; pass DataBase to 32 bit code
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lea rax, DataBase
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mov DWORD PTR DataBaseAdr, eax;
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; prepare MyAsmEntryPatchCode:
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; patch MyAsmEntryPatchCode with address of MyAsmJumpFromKernel
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lea rax, MyAsmJumpFromKernel
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mov DWORD PTR MyAsmEntryPatchCodeJumpFromKernelPlaceholder, eax
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ret
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MyAsmPrepareJumpFromKernel ENDP
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;------------------------------------------------------------------------------
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; Code that is used for patching kernel entry to jump back
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; to our code (to MyAsmJumpFromKernel):
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; - load ecx (rcx) with address to MyAsmJumpFromKernel
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; - jump to MyAsmJumpFromKernel
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; The same generated opcode must run properly in both 32 and 64 bit.
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; 64 bit:
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; - we must set rcx to 0 (upper 4 bytes) before loading ecx with address (lower 4 bytes of rcx)
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; - this requires xor %rcx, %rcx
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; - and that opcode contains 0x48 in front of 32 bit xor %ecx, %ecx
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; 32 bit:
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; - 0x48 opcode is dec %eax in 32 bit
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; - and then we must inc %eax later if 32 bit is detected in MyAsmJumpFromKernel
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;
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; This code is patched with address of MyAsmJumpFromKernel
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; (into MyAsmEntryPatchCodeJumpFromKernelPlaceholder)
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; and then copied to kernel entry address by KernelEntryPatchJump()
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;------------------------------------------------------------------------------
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MyAsmEntryPatchCode PROC
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; .code32
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; dec %eax # -> 48
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; xor %ecx, %ecx # -> 31 C9
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; .byte 0xb9 # movl $0x11223344, %ecx -> B9 44 33 22 11
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;MyAsmEntryPatchCodeJumpFromKernelPlaceholder:
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; .long 0x11223344
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; call *%ecx # -> FF D1
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; jmp *%ecx # -> FF E1
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xor rcx, rcx ; -> 48 31 (33) C9
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db 0B9h ; mov DWORD PTR ecx, $0x11223344 -> B9 44 33 22 11
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MyAsmEntryPatchCodeJumpFromKernelPlaceholder dd 011223344h
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call rcx ; -> FF D1
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; ;jmp *%rcx ; -> FF E1
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MyAsmEntryPatchCode ENDP
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MyAsmEntryPatchCodeEnd:
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;------------------------------------------------------------------------------
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; MyAsmJumpFromKernel
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;
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; Callback from boot.efi - this is where we jump when boot.efi jumps to kernel.
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;
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; - test if we are in 32 bit or in 64 bit
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; - if 64 bit, then jump to MyAsmJumpFromKernel64
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; - else just continue with MyAsmJumpFromKernel32
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;------------------------------------------------------------------------------
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MyAsmJumpFromKernel PROC
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; # writing in 32 bit, but code must run in 64 bit also
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; .code32
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; push %eax # save bootArgs pointer to stack
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; movl $0xc0000080, %ecx # EFER MSR number.
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; rdmsr # Read EFER.
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; bt $8, %eax # Check if LME==1 -> CF=1.
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; pop %eax
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; jc MyAsmJumpFromKernel64 # LME==1 -> jump to 64 bit code
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; # otherwise, continue with MyAsmJumpFromKernel32
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; # but first add 1 to it since it was decremented in 32 bit
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; # in MyAsmEntryPatchCode
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; inc %eax
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; above code in 32 bit gives opcode
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; that is equivalent to following in 64 bit
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push rax ; save bootArgs pointer to stack
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mov ecx, 0c0000080h ; EFER MSR number.
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rdmsr ; Read EFER.
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bt eax, 8 ; Check if LME==1 -> CF=1.
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pop rax
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jc MyAsmJumpFromKernel64 ; LME==1 -> jump to 64 bit code
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; otherwise, continue with MyAsmJumpFromKernel32
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; but first add 1 to it since it was decremented in 32 bit
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; in MyAsmEntryPatchCode
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db 040h ; inc eax
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MyAsmJumpFromKernel ENDP
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;------------------------------------------------------------------------------
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; MyAsmJumpFromKernel32
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;
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; Callback from boot.efi in 32 bit mode.
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; State is prepared for kernel: 32 bit, no paging, pointer to bootArgs in eax.
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;
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; MS 64 bit compiler generates only 64 bit opcode, but this function needs
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; combined 32 and 64 bit code. Code can be written only with 64 bit instructions,
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; but generated opcode must be valid 32 bit. This is a big issue.
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; Well, I guess I know now how the guys in Intel are feeling when
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; they have to work with MS tools on a similar code.
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;
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; Another problem is that it's not possible to access saved variables
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; from 32 bit code (64 bit code has relative addresses, but 32 bit does not
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; and depends on fixes during load and that is not happening sice
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; generated code is marked 64 bit, or something similar).
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; To overcome this, starting address of ou DataBase is passed in runtime - stored
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; to DataBaseAdr below as an argument to mov.
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;------------------------------------------------------------------------------
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MyAsmJumpFromKernel32 PROC
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;hlt ; uncomment to stop here for test
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; save bootArgs pointer to edi
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mov edi, eax
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; load ebx with DataBase - we'll access our saved data with it
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db 0BBh ; mov ebx, OFFSET DataBase
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DataBaseAdr dd 0
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; let's find out kernel entry point - we'll need it to jump back.
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; we are called with
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; dec eax
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; xor ecx, ecx
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; mov 011223344h, ecx
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; call ecx
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; and that left return addr on stack. those instructions
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; are 10 bytes long, and if we take address from stack and
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; substitute 10 from it, we will get kernel entry point.
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pop rcx ; 32 bit: pop ecx
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sub ecx, 10
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; and save it
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mov DWORD PTR [rbx + AsmKernelEntryOff], ecx
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; lets save 32 bit state to be able to recover it later
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; rbx is ebx in 32 bit
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sgdt FWORD PTR [rbx + SavedGDTR32Off]
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sidt FWORD PTR [rbx + SavedIDTR32Off]
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mov WORD PTR [rbx + SavedCS32Off], cs
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mov WORD PTR [rbx + SavedDS32Off], ds
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mov DWORD PTR [rbx + SavedESP32Off], esp
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;
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; move to 64 bit mode ...
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;
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; FIXME: all this with interrupts enabled? no-no
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; load saved UEFI GDT, IDT
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; will become active after code segment is changed in long jump
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; rbx is ebx in 32 bit
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lgdt FWORD PTR [rbx + SavedGDTROff]
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lidt FWORD PTR [rbx + SavedIDTROff]
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; enable the 64-bit page-translation-table entries by setting CR4.PAE=1
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mov rax, cr4
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bts eax, 5
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mov cr4, rax
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; set the long-mode page tables - reuse saved UEFI tables
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mov eax, DWORD PTR [rbx +SavedCR3Off]
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mov cr3, rax
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; enable long mode (set EFER.LME=1).
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mov ecx, 0c0000080h ; EFER MSR number.
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rdmsr ; Read EFER.
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bts eax, 8 ; Set LME=1.
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wrmsr ; Write EFER.
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; enable paging to activate long mode (set CR0.PG=1)
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mov rax, cr0 ; Read CR0.
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bts eax, 31 ; Set PG=1.
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mov cr0, rax ; Write CR0.
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; jump to the 64-bit code segment
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mov ax, WORD PTR [rbx + SavedCSOff]
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push rax
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call _RETF32
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;
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; aloha!
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; if there is any luck, we are in 64 bit mode now
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;
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;hlt ; uncomment to stop here for test
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; set segmens
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mov ax, WORD PTR [rbx + SavedDSOff]
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mov ds, ax
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; set up stack ...
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; not sure if needed, but lets set ss to ds
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mov ss, ax ; disables interrupts for 1 instruction to load rsp
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; lets align the stack
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; mov rax, rsp
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; and rax, 0xfffffffffffffff0
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; mov rsp, rax
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and rsp, 0xfffffffffffffff0
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; call our C code
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; (calling conv.: always reserve place for 4 args on stack)
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; KernelEntryPatchJumpBack (rcx = rax = bootArgs, rdx = 0 = 32 bit kernel jump)
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mov rcx, rdi
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xor rdx, rdx
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push rdx
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push rdx
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push rdx
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push rcx
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; TEST 64 bit jump
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; mov rax, rdi
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; mov rdx, QWORD PTR AsmKernelEntry
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; jmp rdx
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; TEST end
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; KernelEntryPatchJumpBack should be EFIAPI
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; and rbx should not be changed by EFIAPI calling convention
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call KernelEntryPatchJumpBack
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;hlt ; uncomment to stop here for test
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; return value in rax is bootArgs pointer
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mov rdi, rax
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;
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; time to go back to 32 bit
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;
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; FIXME: all this with interrupts enabled? no-no
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; load saved 32 bit gdtr
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lgdt FWORD PTR [rbx + SavedGDTR32Off]
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; push saved cs and rip (with call) to stack and do retf
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mov ax, WORD PTR [rbx + SavedCS32Off]
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push rax
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call _RETF64
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;
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; ok, 32 bit opcode again from here
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;
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; disable paging (set CR0.PG=0)
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mov rax, cr0 ; Read CR0.
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btr eax, 31 ; Set PG=0.
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mov cr0, rax ; Write CR0.
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; disable long mode (set EFER.LME=0).
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mov ecx, 0c0000080h ; EFER MSR number.
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rdmsr ; Read EFER.
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btr eax, 8 ; Set LME=0.
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wrmsr ; Write EFER.
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jmp toNext
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toNext:
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;
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; we are in 32 bit protected mode, no paging
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;
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; now reload saved 32 bit state data
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lidt FWORD PTR [rbx + SavedIDTR32Off]
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mov ax, WORD PTR [rbx + SavedDS32Off]
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mov ds, ax
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mov es, ax
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mov fs, ax
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mov gs, ax
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mov ss, ax ; disables interrupts for 1 instruction to load esp
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mov esp, DWORD PTR [rbx + SavedESP32Off]
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;
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; prepare vars for copying kernel to proper mem
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; and jump to kernel: set registers as needed
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; by MyAsmCopyAndJumpToKernel32
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;
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; boot args back from edi
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mov eax, edi
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; kernel entry point
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mov edx, DWORD PTR [rbx + AsmKernelEntryOff]
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; source, destination and size for kernel copy
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mov esi, DWORD PTR [rbx + AsmKernelImageStartRelocOff]
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mov edi, DWORD PTR [rbx + AsmKernelImageStartOff]
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mov ecx, DWORD PTR [rbx + AsmKernelImageSizeOff]
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; address of relocated MyAsmCopyAndJumpToKernel32
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mov ebx, DWORD PTR [rbx + MyAsmCopyAndJumpToKernel32AddrOff]
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; note: ebx not valid as a pointer to DataBase any more
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;
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; jump to MyAsmCopyAndJumpToKernel32
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;
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jmp QWORD PTR rbx ; jmp DWORD PTR ebx in 32 bit
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_RETF64:
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DB 048h
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_RETF32:
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retf
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; the following is not used - it's here just for a reference
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; jump to the 64-bit code segment
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; as xnu kernel does it
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; example:
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; 07f8437a4: 68 28 00 00 cb = push 0cb000008h - last word on stack is segment 0x0008, 07f8437a8h contains CB opcode which is retf
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; 07f8437a9: e8 fa ff ff ff = call 07f8437a8h - push EIP on stack and continue with 07f8437a8h which is retf
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; retf does far return to next instr after 'call $-1'
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push ((0cbh SHL 24) OR CODE64_SEL)
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call $-1
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MyAsmJumpFromKernel32 ENDP
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;------------------------------------------------------------------------------
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; MyAsmJumpFromKernel64
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;
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; Callback from boot.efi in 64 bit mode.
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; State is prepared for kernel: 64 bit, pointer to bootArgs in rax.
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;------------------------------------------------------------------------------
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MyAsmJumpFromKernel64 PROC
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; let's find out kernel entry point - we'll need it to jump back.
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pop rcx
|
|
sub rcx, 10
|
|
; and save it
|
|
mov QWORD PTR AsmKernelEntry, rcx
|
|
|
|
; call our C code
|
|
; (calling conv.: always reserve place for 4 args on stack)
|
|
; KernelEntryPatchJumpBack (rcx = rax = bootArgs, rdx = 1 = 64 bit kernel jump)
|
|
mov rcx, rax
|
|
xor rdx, rdx
|
|
inc edx
|
|
push rdx
|
|
push rdx
|
|
push rdx
|
|
push rcx
|
|
; KernelEntryPatchJumpBack should be EFIAPI
|
|
call KernelEntryPatchJumpBack
|
|
;hlt ; uncomment to stop here for test
|
|
; return value in rax is bootArgs pointer
|
|
|
|
;
|
|
; prepare vars for copying kernel to proper mem
|
|
; and jump to kernel: set registers as needed
|
|
; by MyAsmCopyAndJumpToKernel64
|
|
;
|
|
|
|
; kernel entry point
|
|
mov rdx, QWORD PTR AsmKernelEntry
|
|
|
|
; source, destination and size for kernel copy
|
|
mov rsi, QWORD PTR AsmKernelImageStartReloc
|
|
mov rdi, QWORD PTR AsmKernelImageStart
|
|
mov rcx, QWORD PTR AsmKernelImageSize
|
|
|
|
; address of relocated MyAsmCopyAndJumpToKernel64
|
|
mov rbx, QWORD PTR MyAsmCopyAndJumpToKernel64Addr
|
|
|
|
;
|
|
; jump to MyAsmCopyAndJumpToKernel64
|
|
;
|
|
jmp rbx
|
|
ret
|
|
MyAsmJumpFromKernel64 ENDP
|
|
|
|
|
|
;------------------------------------------------------------------------------
|
|
; MyAsmCopyAndJumpToKernel
|
|
;
|
|
; This is the last part of the code - it will copy kernel image from reloc
|
|
; block to proper mem place and jump to kernel.
|
|
; There are separate versions for 32 and 64 bit.
|
|
; This code will be relocated (copied) to higher mem by PrepareJumpFromKernel().
|
|
;------------------------------------------------------------------------------
|
|
align 08h
|
|
MyAsmCopyAndJumpToKernel:
|
|
|
|
;------------------------------------------------------------------------------
|
|
; MyAsmCopyAndJumpToKernel32
|
|
;
|
|
; Expects:
|
|
; EAX = address of boot args (proper address, not from reloc block)
|
|
; EDX = kernel entry point
|
|
; ESI = start of kernel image in reloc block (source)
|
|
; EDI = proper start of kernel image (destination)
|
|
; ECX = kernel image size in bytes
|
|
;------------------------------------------------------------------------------
|
|
MyAsmCopyAndJumpToKernel32 PROC
|
|
|
|
;
|
|
; we will move double words (4 bytes)
|
|
; so ajust ECX to number of double words.
|
|
; just in case ECX is not multiple of 4 - inc by 1
|
|
;
|
|
shr ecx, 2
|
|
db 041h ; inc ecx
|
|
|
|
;
|
|
; copy kernel image from reloc block to proper mem place.
|
|
; all params should be already set:
|
|
; ECX = number of double words
|
|
; DS:ESI = source
|
|
; ES:EDI = destination
|
|
;
|
|
cld ; direction is up
|
|
rep movsd
|
|
|
|
;
|
|
; and finally jump to kernel:
|
|
; EAX already contains bootArgs pointer,
|
|
; and EDX contains kernel entry point
|
|
;
|
|
;hlt
|
|
jmp QWORD PTR rdx ; jmp DWORD PTR edx in 32 bit
|
|
MyAsmCopyAndJumpToKernel32 ENDP
|
|
MyAsmCopyAndJumpToKernel32End:
|
|
|
|
|
|
;------------------------------------------------------------------------------
|
|
; MyAsmCopyAndJumpToKernel64
|
|
;
|
|
; Expects:
|
|
; RAX = address of boot args (proper address, not from reloc block)
|
|
; RDX = kernel entry point
|
|
; RSI = start of kernel image in reloc block (source)
|
|
; RDI = proper start of kernel image (destination)
|
|
; RCX = kernel image size in bytes
|
|
;------------------------------------------------------------------------------
|
|
align 08h
|
|
MyAsmCopyAndJumpToKernel64 PROC
|
|
|
|
;
|
|
; we will move quad words (8 bytes)
|
|
; so ajust RCX to number of double words.
|
|
; just in case RCX is not multiple of 8 - inc by 1
|
|
;
|
|
shr rcx, 3
|
|
inc rcx
|
|
|
|
;
|
|
; copy kernel image from reloc block to proper mem place.
|
|
; all params should be already set:
|
|
; RCX = number of double words
|
|
; RSI = source
|
|
; RDI = destination
|
|
;
|
|
cld ; direction is up
|
|
rep movsq
|
|
|
|
;
|
|
; and finally jump to kernel:
|
|
; RAX already contains bootArgs pointer,
|
|
; and RDX contains kernel entry point
|
|
;
|
|
; hlt
|
|
jmp QWORD PTR rdx
|
|
|
|
MyAsmCopyAndJumpToKernel64 ENDP
|
|
MyAsmCopyAndJumpToKernel64End:
|
|
|
|
MyAsmCopyAndJumpToKernelEnd:
|
|
|
|
END
|
|
|