gdt.h

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/*******************************************************************************/
/*  © Université de Lille, The Pip Development Team (2015-2021)                */
/*                                                                             */
/*  This software is a computer program whose purpose is to run a minimal,     */
/*  hypervisor relying on proven properties such as memory isolation.          */
/*                                                                             */
/*  This software is governed by the CeCILL license under French law and       */
/*  abiding by the rules of distribution of free software.  You can  use,      */
/*  modify and/ or redistribute the software under the terms of the CeCILL     */
/*  license as circulated by CEA, CNRS and INRIA at the following URL          */
/*  "http://www.cecill.info".                                                  */
/*                                                                             */
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/*  modify and redistribute granted by the license, users are provided only    */
/*  with a limited warranty  and the software's author,  the holder of the     */
/*  economic rights,  and the successive licensors  have only  limited         */
/*  liability.                                                                 */
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/*  software by the user in light of its specific status of free software,     */
/*  that may mean  that it is complicated to manipulate,  and  that  also      */
/*  therefore means  that it is reserved for developers  and  experienced      */
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/*******************************************************************************/

#ifndef __GDT__
#define __GDT__

#include <stdint.h>
#include "maldefines.h"

struct segment_descriptor_s
{
    unsigned limit_low   : 16; 
    unsigned base_low    : 16; 
    unsigned base_middle :  8; 
    unsigned type        :  4; 
    unsigned s           :  1; 
    unsigned dpl         :  2; 
    unsigned present     :  1; 
    unsigned limit_high  :  4; 
    unsigned avl         :  1; 
    unsigned l           :  1; 
    unsigned d_b         :  1; 
    unsigned granularity :  1; 
    unsigned base_high   :  8; 
};

#define GRANULARITY_1    0
#define GRANULARITY_4096 1

#define SEG_DATA_READONLY_EXPANDUP_TYPE      0b0000
#define SEG_DATA_READWRITE_EXPANDUP_TYPE     0b0010
#define SEG_DATA_READONLY_EXPANDDOWN_TYPE    0b0100
#define SEG_DATA_READWRITE_EXPANDDOWN_TYPE   0b0110

#define SEG_CODE_EXECONLY_NONCONFORMING_TYPE 0b1000
#define SEG_CODE_EXECREAD_NONCONFORMING_TYPE 0b1010
#define SEG_CODE_EXECONLY_CONFORMING_TYPE    0b1100
#define SEG_CODE_EXECREAD_CONFORMING_TYPE    0b1110

typedef struct segment_descriptor_s segment_descriptor_t;

struct callgate_descriptor_s {
    unsigned offset_low  : 16; 
    unsigned segment     : 16; 
    unsigned args        :  5; 
    unsigned reserved    :  3; 
    unsigned type        :  4; 
    unsigned zero        :  1; 
    unsigned dpl         :  2; 
    unsigned present     :  1; 
    unsigned offset_high : 16; 
};

#define GDT_CALLGATE_TYPE 0b1100

typedef struct callgate_descriptor_s callgate_descriptor_t;

struct tss_descriptor_s {
    unsigned limit_low   : 16; //<! Segment limit 15..0
    unsigned base_low    : 16; //<! Segment base address 15..0
    unsigned base_middle :  8; //<! Segment base address 23..16
    unsigned type        :  4; //<! GDT_TSS_BUSY_TYPE or GDT_TSS_INACTIVE_TYPE
    unsigned zero        :  1; //<! Always zero smh
    unsigned dpl         :  2; //<! Descriptor Privilege Level
    unsigned present     :  1; //<! Present flag (validity of descriptor)
    unsigned limit_high  :  4; //<! Segment limit 19..16
    unsigned avl         :  1; //<! Available for use by system software
    unsigned zero2       :  2; //<! Also always zero smh
    unsigned granularity :  1; //<! 0 => segment limit range from 1B to 1MB, byte per byte
                                   //<! 1 => segment limit range from 4kB to 4GB, 4kB per 4kB
                                   /*   When the G flag is 0 in a TSS descriptor for a 32-bit
                    *   TSS, the limit field must have a value equal to or
                                    *   greater than 67H, one byte less than the minimum size
                                    *   of a TSS. Otherwise, TS fault is generated.
                                    */
    unsigned base_high   :  8; //<! Segment base address 31..24
};

#define GDT_TSS_INACTIVE_TYPE 0b1001 //inactive task
#define GDT_TSS_BUSY_TYPE     0b1011 //running or suspended task (interrupted state)

typedef struct tss_descriptor_s tss_descriptor_t;

union gdt_entry {
    segment_descriptor_t segment_desc;
    callgate_descriptor_t callgate_desc;
    tss_descriptor_t tss_desc;
    uint64_t null_desc;
};

typedef union gdt_entry gdt_entry_t;

struct gdt_ptr
{
    unsigned short limit; 
    unsigned int base; 
} __attribute__((packed));

struct tss_s {
    unsigned prev_tss   : 16; 
    unsigned reserved0  : 16;
    unsigned esp0       : 32; 
    unsigned ss0        : 16; 
    unsigned reserved1  : 16;
    unsigned esp1       : 32; 
    unsigned ss1        : 16; 
    unsigned reserved2  : 16;
    unsigned esp2       : 32; 
    unsigned ss2        : 16; 
    unsigned reserved3  : 16;
    unsigned cr3        : 32; 
    unsigned eip        : 32; 
    unsigned eflags     : 32; 
    unsigned eax        : 32; 
    unsigned ecx        : 32; 
    unsigned edx        : 32; 
    unsigned ebx        : 32; 
    unsigned esp        : 32; 
    unsigned ebp        : 32; 
    unsigned esi        : 32; 
    unsigned edi        : 32; 
    unsigned es         : 16; 
    unsigned reserved4  : 16;
    unsigned cs         : 16; 
    unsigned reserved5  : 16;
    unsigned ss         : 16; 
    unsigned reserved6  : 16;
    unsigned ds         : 16; 
    unsigned reserved7  : 16;
    unsigned fs         : 16; 
    unsigned reserved8  : 16;
    unsigned gs         : 16; 
    unsigned reserved9  : 16;
    unsigned ldt        : 16; 
    unsigned reserved10 : 16;
    unsigned trap       :  1; 
    unsigned reserved11 : 15;
    unsigned iomap_base : 16; 
} __attribute__((packed));

typedef struct tss_s tss_t;
extern tss_t tss;

void gdt_init();

void setKernelStack(uint32_t stack);

#endif