83 lines
2.0 KiB
C++
83 lines
2.0 KiB
C++
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#include "pe_checksum.h"
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#include "pe_structures.h"
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#include "pe_base.h"
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namespace pe_bliss
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{
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using namespace pe_win;
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//Calculate checksum of image
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uint32_t calculate_checksum(std::istream& file)
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{
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//Save istream state
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std::ios_base::iostate state = file.exceptions();
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std::streamoff old_offset = file.tellg();
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//Checksum value
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unsigned long long checksum = 0;
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try
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{
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image_dos_header header;
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file.exceptions(std::ios::goodbit);
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//Read DOS header
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pe_base::read_dos_header(file, header);
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//Calculate PE checksum
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file.seekg(0);
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unsigned long long top = 0xFFFFFFFF;
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top++;
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//"CheckSum" field position in optional PE headers - it's always 64 for PE and PE+
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static const unsigned long checksum_pos_in_optional_headers = 64;
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//Calculate real PE headers "CheckSum" field position
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//Sum is safe here
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unsigned long pe_checksum_pos = header.e_lfanew + sizeof(image_file_header) + sizeof(uint32_t) + checksum_pos_in_optional_headers;
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//Calculate checksum for each byte of file
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std::streamoff filesize = pe_utils::get_file_size(file);
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for(long long i = 0; i < filesize; i += 4)
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{
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unsigned long dw = 0;
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//Read DWORD from file
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file.read(reinterpret_cast<char*>(&dw), sizeof(unsigned long));
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//Skip "CheckSum" DWORD
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if(i == pe_checksum_pos)
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continue;
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//Calculate checksum
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checksum = (checksum & 0xffffffff) + dw + (checksum >> 32);
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if(checksum > top)
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checksum = (checksum & 0xffffffff) + (checksum >> 32);
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}
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//Finish checksum
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checksum = (checksum & 0xffff) + (checksum >> 16);
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checksum = (checksum) + (checksum >> 16);
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checksum = checksum & 0xffff;
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checksum += static_cast<unsigned long>(filesize);
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}
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catch(const std::exception&)
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{
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//If something went wrong, restore istream state
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file.exceptions(state);
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file.seekg(old_offset);
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file.clear();
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//Rethrow
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throw;
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}
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//Restore istream state
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file.exceptions(state);
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file.seekg(old_offset);
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file.clear();
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//Return checksum
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return static_cast<uint32_t>(checksum);
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}
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}
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