143 lines
4.6 KiB
C
143 lines
4.6 KiB
C
#include <stdint.h>
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#define SEG_DESCTYPE(x) ((x) << 0x04) // Descriptor type (0 for system, 1 for code/data)
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#define SEG_PRES(x) ((x) << 0x07) // Present
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#define SEG_SAVL(x) ((x) << 0x0C) // Available for system use
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#define SEG_LONG(x) ((x) << 0x0D) // Long mode
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#define SEG_SIZE(x) ((x) << 0x0E) // Size (0 for 16-bit, 1 for 32)
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#define SEG_GRAN(x) ((x) << 0x0F) // Granularity (0 for 1B - 1MB, 1 for 4KB - 4GB)
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#define SEG_PRIV(x) (((x) & 0x03) << 0x05) // Set privilege level (0 - 3)
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#define SEG_DATA_RD 0x00 // Read-Only
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#define SEG_DATA_RDA 0x01 // Read-Only, accessed
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#define SEG_DATA_RDWR 0x02 // Read/Write
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#define SEG_DATA_RDWRA 0x03 // Read/Write, accessed
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#define SEG_DATA_RDEXPD 0x04 // Read-Only, expand-down
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#define SEG_DATA_RDEXPDA 0x05 // Read-Only, expand-down, accessed
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#define SEG_DATA_RDWREXPD 0x06 // Read/Write, expand-down
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#define SEG_DATA_RDWREXPDA 0x07 // Read/Write, expand-down, accessed
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#define SEG_CODE_EX 0x08 // Execute-Only
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#define SEG_CODE_EXA 0x09 // Execute-Only, accessed
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#define SEG_CODE_EXRD 0x0A // Execute/Read
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#define SEG_CODE_EXRDA 0x0B // Execute/Read, accessed
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#define SEG_CODE_EXC 0x0C // Execute-Only, conforming
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#define SEG_CODE_EXCA 0x0D // Execute-Only, conforming, accessed
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#define SEG_CODE_EXRDC 0x0E // Execute/Read, conforming
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#define SEG_CODE_EXRDCA 0x0F // Execute/Read, conforming, accessed
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#define GDT_CODE_PL0 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
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SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
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SEG_PRIV(0) | SEG_CODE_EXRD
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#define GDT_DATA_PL0 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
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SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
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SEG_PRIV(0) | SEG_DATA_RDWR
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#define GDT_CODE_PL3 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
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SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
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SEG_PRIV(3) | SEG_CODE_EXRD
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#define GDT_DATA_PL3 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
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SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
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SEG_PRIV(3) | SEG_DATA_RDWR
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typedef struct __attribute__((packed)) {
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uint16_t limit;
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uint32_t base;
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} gdt_ptr_t;
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typedef struct __attribute__((packed)) {
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uint32_t prev_tss;
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uint32_t esp0;
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uint32_t ss0;
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uint32_t esp1;
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uint32_t ss1;
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uint32_t esp2;
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uint32_t ss2;
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uint32_t cr3;
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uint32_t eip;
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uint32_t eflags;
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uint32_t eax;
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uint32_t ecx;
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uint32_t edx;
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uint32_t ebx;
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uint32_t esp;
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uint32_t ebp;
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uint32_t esi;
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uint32_t edi;
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uint32_t es;
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uint32_t cs;
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uint32_t ss;
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uint32_t ds;
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uint32_t fs;
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uint32_t gs;
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uint32_t ldt;
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uint16_t trap;
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uint16_t iomap_base;
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} tss_entry;
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uint64_t gdt[6];
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gdt_ptr_t gdtr;
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tss_entry tss;
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extern void load_gdt();
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extern void tss_flush();
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static uint64_t create_descriptor(uint32_t base, uint32_t limit, uint16_t flag)
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{
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uint64_t descriptor;
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descriptor = limit & 0x000F0000;
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descriptor |= (flag << 8) & 0x00F0FF00;
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descriptor |= (base >> 16) & 0x000000FF;
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descriptor |= base & 0xFF000000;
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descriptor <<= 32;
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descriptor |= base << 16;
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descriptor |= limit & 0x0000FFFF;
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return descriptor;
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}
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static uint64_t create_tss_descriptor(uint32_t base, uint32_t limit)
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{
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uint64_t descriptor;
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uint16_t tss_flags = SEG_PRES(1) | SEG_PRIV(0) | SEG_DESCTYPE(0) | 0x09;
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descriptor = limit & 0x000F0000;
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descriptor |= (tss_flags << 8) & 0x00F0FF00;
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descriptor |= (base >> 16) & 0x000000FF;
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descriptor |= base & 0xFF000000;
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descriptor <<= 32;
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descriptor |= base << 16;
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descriptor |= limit & 0x0000FFFF;
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return descriptor;
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}
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void init_gdt() {
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gdt[0] = create_descriptor(0, 0, 0);
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gdt[1] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL0));
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gdt[2] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL0));
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gdt[3] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL3));
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gdt[4] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL3));
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for (uint32_t i = 0; i < sizeof(tss_entry); i++) {
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((char*)&tss)[i] = 0;
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}
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tss.ss0 = 0x10;
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tss.iomap_base = sizeof(tss_entry);
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gdt[5] = create_tss_descriptor((uint32_t)&tss, sizeof(tss_entry) - 1);
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gdtr.limit = 6 * sizeof(uint64_t) - 1;
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gdtr.base = (uint32_t)&gdt;
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load_gdt();
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tss_flush();
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}
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