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Remove PIC functionality from syscall.asm

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Makes things easier
This commit is contained in:
Nero 2021-01-13 17:38:20 +00:00
parent 23c6223055
commit df243e668e
1 changed files with 28 additions and 52 deletions
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80
kernel/syscall.asm
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@ -11,7 +11,7 @@ section .bss
curpsp: resw 1 curpsp: resw 1
section .data section .rodata
stab: ; syscall table stab: ; syscall table
; cells: ptr to handler, ptr to sysret ; cells: ptr to handler, ptr to sysret
@ -47,7 +47,6 @@ absolute 0
; saved userdata ; saved userdata
PSPAX: resw 1 PSPAX: resw 1
PSPCX: resw 1 PSPCX: resw 1
PSPBP: resw 1
; SS:SP ; SS:SP
PSPSP: resw 1 PSPSP: resw 1
PSPSS: resw 1 PSPSS: resw 1
@ -63,59 +62,35 @@ PSPDD: resb 1
section .text section .text
; Load current PSP segment into DS ; WARNING: BP, SI and DI are not saved
; OUT ds PSP segment ; If kernel code uses them, they need to be saved to the stack
; ax 0
pspds: xor ax, ax
mov ds, ax
mov ds, [curpsp]
ret
; Get reloc offset into CX
reloff: call .l01
.l01: pop cx
sub cx, .l01
ret
int21: push ds int21: push ds
; load program PSP and save userdata ; load program PSP and save userdata
push ax mov ds, [cs:curpsp]
call pspds
pop word [PSPAX]
pop word [PSPDS] pop word [PSPDS]
mov [PSPCX], cx
mov [PSPBP], bp
mov [PSPSS], ss
mov [PSPSP], sp
mov [PSPDX], dx
mov [PSPES], es mov [PSPES], es
mov [PSPAX], ax
mov [PSPCX], cx
mov [PSPDX], dx
mov [PSPBX], bx mov [PSPBX], bx
mov ss, ax mov [PSPSS], ss
mov [PSPSP], sp
xor bx, bx
mov ss, bx
mov sp, stack mov sp, stack
; get offset for PIC
call reloff
; get ptr into syscall table ; get ptr into syscall table
mov al, [PSPAX+1] ; ah is still 0 mov bl, [PSPAX+1] ; bh is still 0
shl ax, 1 shl bx, 1
shl ax, 1 shl bx, 1
add ax, stab add bx, stab
add ax, cx ; load sysret and handler ptr
mov bx, ax push word [cs:bx+2]
; load sysret ptr push word [cs:bx]
mov ax, [cs:bx+2] ; restore user data and launch ret chain
add ax, cx
push ax
; load handler ptr
mov ax, [cs:bx]
add ax, cx
push ax
; restore user data
mov ax, [PSPAX]
mov cx, [PSPCX]
mov bx, [PSPBX] mov bx, [PSPBX]
mov ds, [PSPDS]
; launch ROP chain
ret ret
err: mov ah, 0xFF err: mov ah, 0xFF
@ -123,25 +98,26 @@ err: mov ah, 0xFF
; sysret handlers ; sysret handlers
; return ES:BX to user ; return ES:BX to user
sretd: mov ds, [ss:curpsp] sretd: mov ds, [cs:curpsp]
jmp sret.l02 jmp sret.l02
; return BX to user ; return BX to user
sretw: mov ds, [ss:curpsp] sretw: mov ds, [cs:curpsp]
mov es, [PSPES] mov es, [PSPES]
jmp sret.l02 jmp sret.l02
; return AL to user ; return AL to user
sretb: mov ds, [ss:curpsp] sretb: mov ds, [cs:curpsp]
mov ah, [PSPAX+1] mov ah, [PSPAX+1]
les bx, [PSPBX] les bx, [PSPBX]
jmp sret.l03 jmp sret.l03
; return without result ; return without result
sret: mov ds, [ss:curpsp] sret: mov ds, [cs:curpsp]
.l01: les bx, [PSPBX] les bx, [PSPBX]
.l02: mov ax, [PSPAX] .l02: mov ax, [PSPAX]
.l03: mov ss, [PSPSS] .l03: mov ss, [PSPSS]
mov sp, [PSPSP] mov sp, [PSPSP]
lds dx, [PSPDX] mov cx, [PSPCX]
lds dx, [PSPDX] ; DS last
iret iret