111 lines
3.5 KiB
C
111 lines
3.5 KiB
C
/*++
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Copyright (c) 1991 Microsoft Corporation
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Module Name:
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imagedir.c
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Abstract:
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The module contains the code to translate an image directory type to the address of the data for that entry.
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Author:
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Steve Wood (stevewo) 18-Aug-1989
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Environment:
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User Mode or Kernel Mode
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--*/
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#include "ntrtlp.h"
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// Define forward referenced prootypes.
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USHORT ChkSum(ULONG PartialSum, PUSHORT Source, ULONG Length);
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#if defined(ALLOC_PRAGMA) && defined(NTOS_KERNEL_RUNTIME)
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#if !defined(_IA64_)
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#pragma alloc_text(PAGE,ChkSum)
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#endif // !defined(_IA64_)
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#pragma alloc_text(PAGE,LdrVerifyMappedImageMatchesChecksum)
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#endif
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#if !defined(_IA64_)
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USHORT ChkSum(ULONG PartialSum, PUSHORT Source, ULONG Length)
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/*++
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Routine Description:
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Compute a partial checksum on a portion of an imagefile.
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Arguments:
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PartialSum - Supplies the initial checksum value.
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Sources - Supplies a pointer to the array of words for which the checksum is computed.
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Length - Supplies the length of the array in words.
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Return Value:
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The computed checksum value is returned as the function value.
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--*/
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{
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RTL_PAGED_CODE();
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// Compute the word wise checksum allowing carries to occur into the high order half of the checksum longword.
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while (Length--) {
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PartialSum += *Source++;
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PartialSum = (PartialSum >> 16) + (PartialSum & 0xffff);
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}
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// Fold final carry into a single word result and return the resultant value.
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return (USHORT)(((PartialSum >> 16) + PartialSum) & 0xffff);
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}
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#endif // !defined(_IA64_)
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BOOLEAN LdrVerifyMappedImageMatchesChecksum (IN PVOID BaseAddress, IN ULONG FileLength)
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/*++
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Routine Description:
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This functions computes the checksum of an image mapped as a data file.
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Arguments:
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BaseAddress - Supplies a pointer to the base of the mapped file.
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FileLength - Supplies the length of the file in bytes.
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Return Value:
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TRUE - The checksum stored in the image matches the checksum of the data.
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FALSE - The checksum in the image is not correct.
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--*/
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{
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PUSHORT AdjustSum;
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PIMAGE_NT_HEADERS NtHeaders;
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USHORT PartialSum;
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ULONG HeaderSum;
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ULONG CheckSum;
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RTL_PAGED_CODE();
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// Compute the checksum of the file and zero the header checksum value.
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HeaderSum = 0;
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PartialSum = ChkSum(0, (PUSHORT)BaseAddress, (FileLength + 1) >> 1);
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// If the file is an image file, then subtract the two checksum words
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// in the optional header from the computed checksum before adding
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// the file length, and set the value of the header checksum.
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NtHeaders = RtlImageNtHeader(BaseAddress);
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if (NtHeaders != NULL) {
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HeaderSum = NtHeaders->OptionalHeader.CheckSum;
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#ifndef NTOS_KERNEL_RUNTIME
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// On Nt 3.1 and 3.5, we allowed printer drivers with 0 checksums into
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// csrss unintentionally. This means that we must allow this forever.
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// I don't want to allow this for kernel mode drivers, so I will only
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// allow 0 checksums of the high order bit is clear ?
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if ( HeaderSum == 0 ) {
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return TRUE;
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}
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#endif // NTOS_KERNEL_RUNTIME
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AdjustSum = (PUSHORT)(&NtHeaders->OptionalHeader.CheckSum);
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PartialSum -= (PartialSum < AdjustSum[0]);
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PartialSum -= AdjustSum[0];
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PartialSum -= (PartialSum < AdjustSum[1]);
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PartialSum -= AdjustSum[1];
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} else {
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PartialSum = 0;
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HeaderSum = FileLength;
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}
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// Compute the final checksum value as the sum of the paritial checksum and the file length.
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CheckSum = (ULONG)PartialSum + FileLength;
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return (CheckSum == HeaderSum);
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} |