Enrico Fraccaroli (Galfurian)
61 lines
1.9 KiB
C
61 lines
1.9 KiB
C
/// @file tss.c
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/// @brief
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/// @copyright (c) 2014-2022 This file is distributed under the MIT License.
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/// See LICENSE.md for details.
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// Include the kernel log levels.
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#include "sys/kernel_levels.h"
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/// Change the header.
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#define __DEBUG_HEADER__ "[TSS ]"
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/// Set the log level.
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#define __DEBUG_LEVEL__ LOGLEVEL_NOTICE
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#include "descriptor_tables/tss.h"
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#include "string.h"
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#include "io/debug.h"
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#include "descriptor_tables/gdt.h"
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static tss_entry_t kernel_tss;
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void tss_init(uint8_t idx, uint32_t ss0)
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{
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uint32_t base = (uint32_t)&kernel_tss;
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uint32_t limit = base + sizeof(tss_entry_t);
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// Add the TSS descriptor to the GDT.
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// Kernel tss, access(E9 = 1 11 0 1 0 0 1)
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// 1 present
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// 11 ring 3 (kernel)
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// 0 always 0 when dealing with system segments
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// 1 execution
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// 0 can not be executed by ring lower or equal to DPL,
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// 0 not readable
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// 1 access bit, always 0, cpu set this to 1 when accessing this sector
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gdt_set_gate(idx, base, limit, GDT_PRESENT | GDT_USER | GDT_EX | GDT_AC, 0x0);
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// Note that we usually set tss's esp to 0 when booting our os, however,
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// we need to set it to the real esp when we've switched to usermode
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// because the CPU needs to know what esp to use when usermode app is
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// calling a kernel function(aka system call), that's why we have a
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// function below called tss_set_stack.
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memset(&kernel_tss, 0x0, sizeof(tss_entry_t));
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kernel_tss.ss0 = ss0;
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kernel_tss.esp0 = 0x0;
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kernel_tss.cs = 0x0b;
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kernel_tss.ds = 0x13;
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kernel_tss.es = 0x13;
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kernel_tss.fs = 0x13;
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kernel_tss.gs = 0x13;
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kernel_tss.ss = 0x13;
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kernel_tss.iomap = sizeof(tss_entry_t);
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}
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void tss_set_stack(uint32_t kss, uint32_t kesp)
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{
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// Kernel data segment.
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kernel_tss.ss0 = kss;
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// Kernel stack address.
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kernel_tss.esp0 = kesp;
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}
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