checksum.c File Reference

#include "ntrtlp.h"

Go to the source code of this file.

Functions
USHORT	ChkSum (ULONG PartialSum, PUSHORT Source, ULONG Length)
BOOLEAN	LdrVerifyMappedImageMatchesChecksum (IN PVOID BaseAddress, IN ULONG FileLength)

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Function Documentation

USHORT ChkSum (  ULONG  PartialSum, PUSHORT  Source, ULONG  Length )

Definition at line 48 of file checksum.c. References RTL_PAGED_CODE, and USHORT. Referenced by LdrVerifyMappedImageMatchesChecksum(). 00056 : 00057 00058 Compute a partial checksum on a portion of an imagefile. 00059 00060 Arguments: 00061 00062 PartialSum - Supplies the initial checksum value. 00063 00064 Sources - Supplies a pointer to the array of words for which the 00065 checksum is computed. 00066 00067 Length - Supplies the length of the array in words. 00068 00069 Return Value: 00070 00071 The computed checksum value is returned as the function value. 00072 00073 --*/ 00074 00075 { 00076 00077 RTL_PAGED_CODE(); 00078 00079 // 00080 // Compute the word wise checksum allowing carries to occur into the 00081 // high order half of the checksum longword. 00082 // 00083 00084 while (Length--) { 00085 PartialSum += *Source++; 00086 PartialSum = (PartialSum >> 16) + (PartialSum & 0xffff); 00087 } 00088 00089 // 00090 // Fold final carry into a single word result and return the resultant 00091 // value. 00092 // 00093 00094 return (USHORT)(((PartialSum >> 16) + PartialSum) & 0xffff); 00095 } #endif // !defined(_IA64_)

BOOLEAN LdrVerifyMappedImageMatchesChecksum (  IN PVOID  BaseAddress, IN ULONG  FileLength )

Definition at line 99 of file checksum.c. References ChkSum(), NULL, PUSHORT, RTL_PAGED_CODE, RtlImageNtHeader(), TRUE, and USHORT. Referenced by LdrVerifyImageMatchesChecksum(), and MmCheckSystemImage(). 00106 : 00107 00108 This functions computes the checksum of an image mapped as a data file. 00109 00110 Arguments: 00111 00112 BaseAddress - Supplies a pointer to the base of the mapped file. 00113 00114 FileLength - Supplies the length of the file in bytes. 00115 00116 Return Value: 00117 00118 TRUE - The checksum stored in the image matches the checksum of the data. 00119 00120 FALSE - The checksum in the image is not correct. 00121 00122 --*/ 00123 00124 { 00125 00126 PUSHORT AdjustSum; 00127 PIMAGE_NT_HEADERS NtHeaders; 00128 USHORT PartialSum; 00129 ULONG HeaderSum; 00130 ULONG CheckSum; 00131 00132 RTL_PAGED_CODE(); 00133 00134 // 00135 // Compute the checksum of the file and zero the header checksum value. 00136 // 00137 00138 HeaderSum = 0; 00139 PartialSum = ChkSum(0, (PUSHORT)BaseAddress, (FileLength + 1) >> 1); 00140 00141 // 00142 // If the file is an image file, then subtract the two checksum words 00143 // in the optional header from the computed checksum before adding 00144 // the file length, and set the value of the header checksum. 00145 // 00146 00147 NtHeaders = RtlImageNtHeader(BaseAddress); 00148 if (NtHeaders != NULL) { 00149 HeaderSum = NtHeaders->OptionalHeader.CheckSum; 00150 00151 #ifndef NTOS_KERNEL_RUNTIME 00152 // 00153 // On Nt 3.1 and 3.5, we allowed printer drivers with 0 checksums into 00154 // csrss unintentionally. This means that we must allow this forever. 00155 // I don't want to allow this for kernel mode drivers, so I will only 00156 // allow 0 checksums of the high order bit is clear ? 00157 // 00158 00159 00160 if ( HeaderSum == 0 ) { 00161 return TRUE; 00162 } 00163 #endif // NTOS_KERNEL_RUNTIME 00164 00165 AdjustSum = (PUSHORT)(&NtHeaders->OptionalHeader.CheckSum); 00166 PartialSum -= (PartialSum < AdjustSum[0]); 00167 PartialSum -= AdjustSum[0]; 00168 PartialSum -= (PartialSum < AdjustSum[1]); 00169 PartialSum -= AdjustSum[1]; 00170 } else { 00171 PartialSum = 0; 00172 HeaderSum = FileLength; 00173 } 00174 00175 // 00176 // Compute the final checksum value as the sum of the paritial checksum 00177 // and the file length. 00178 // 00179 00180 CheckSum = (ULONG)PartialSum + FileLength; 00181 return (CheckSum == HeaderSum); 00182 } }

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