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56 lines
2.4 KiB
56 lines
2.4 KiB
#include "segment_intrin.h"
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namespace segment
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{
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auto get_access_rights(segment_descriptor_64* segment_descriptor) -> vmx_segment_access_rights
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{
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vmx_segment_access_rights result;
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result.granularity = segment_descriptor->granularity;
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result.type = segment_descriptor->type;
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result.descriptor_type = segment_descriptor->descriptor_type;
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result.present = segment_descriptor->present;
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result.long_mode = segment_descriptor->long_mode;
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result.available_bit = segment_descriptor->system;
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result.default_big = segment_descriptor->default_big;
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return result;
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}
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auto get_info(segment_descriptor_register_64 gdt_value, segment_selector segment_selector) -> hv::segment_info_ctx
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{
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hv::segment_info_ctx segment_info;
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// GDT->BaseAddress + (segment index << 3)
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// gives us a pointer to the segment descriptor...
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const auto segment_descriptor =
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reinterpret_cast<segment_descriptor_64*>(
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gdt_value.base_address + (segment_selector.index << SEGMENT_SELECTOR_INDEX_BIT));
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// access rights are spread out over the segment
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// descriptor so those need to picked out and assigned
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// to the vmx segment access rights variable...
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segment_info.limit = __segmentlimit(segment_selector.flags);
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segment_info.rights = get_access_rights(segment_descriptor);
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// base address of a segment is spread over the segment descriptor in 3 places. 2 parts of the
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// address are 8 bits each (1 byte each) and the lowest part of the address is 2 bytes (4 bytes in total)...
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// by shifting the values to the correct bit offset and adding them all together we get the address...
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segment_info.base_addr = (u32)((segment_descriptor->base_address_high << SEGMENT__BASE_ADDRESS_HIGH_BIT) +
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(segment_descriptor->base_address_middle << SEGMENT__BASE_ADDRESS_MIDDLE_BIT) +
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(segment_descriptor->base_address_low));
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// Example:
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// - high bits: 0b1111 0000 0000 0000
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// - middle bits: 0b0000 1111 0000 0000
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// - low bits: 0b0000 0000 1011 1000
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// --------------------- +
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// 0b1111 1111 1011 1000 <==== full address...
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// if you add all of these together you will get the full address...
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// if the base address is 64bits then go ahead
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// and add the top 32bits onto the address..
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if (!segment_descriptor->descriptor_type)
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segment_info.base_addr += ((u64)segment_descriptor->base_address_upper << SEGMENT__BASE_ADDRESS_SHIFT);
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return segment_info;
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}
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} |