probewrt.c File Reference

#include "mi.h"

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Functions
VOID	MmProbeForWrite (IN PVOID Address, IN ULONG Length)

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Function Documentation

VOID MmProbeForWrite (  IN PVOID  Address, IN ULONG  Length )

Definition at line 36 of file probewrt.c. References ExRaiseStatus(), MiGetPteAddress, MmAccessFault(), NT_SUCCESS, PAGE_SIZE, TRUE, _MMPTE::u, and UserMode. 00043 : 00044 00045 This function probes an address for write accessibility on 00046 the Intel 386. 00047 00048 Arguments: 00049 00050 Address - Supplies a pointer to the structure to probe. 00051 00052 Length - Supplies the length of the structure. 00053 00054 Return Value: 00055 00056 None. If the Address cannot be written an exception is raised. 00057 00058 --*/ 00059 00060 { 00061 PMMPTE PointerPte; 00062 PMMPTE LastPte; 00063 MMPTE PteContents; 00064 CCHAR Temp; 00065 00066 // 00067 // Loop on the copy on write case until the page is only 00068 // writable. 00069 // 00070 00071 if (Address >= (PVOID)MM_HIGHEST_USER_ADDRESS) { 00072 ExRaiseStatus(STATUS_ACCESS_VIOLATION); 00073 } 00074 00075 PointerPte = MiGetPteAddress (Address); 00076 LastPte = MiGetPteAddress ((PVOID)((ULONG)Address + Length - 1)); 00077 00078 while (PointerPte <= LastPte) { 00079 00080 for (;;) { 00081 00082 // 00083 // Touch the address as a byte to check for readability and 00084 // get the PTE built. 00085 // 00086 00087 do { 00088 Temp = *(volatile CCHAR *)Address; 00089 PteContents = *(volatile MMPTE *)PointerPte; 00090 } while (PteContents.u.Hard.Valid == 0); 00091 00092 if (PteContents.u.Hard.Write == 1) { 00093 00094 // 00095 // The PTE is writable and not copy on write. 00096 // 00097 00098 break; 00099 } 00100 00101 if (PteContents.u.Hard.CopyOnWrite == 1) { 00102 00103 // 00104 // The PTE is copy on write. Call the pager and let 00105 // it deal with this. Once the page fault is complete, 00106 // this loop will again be repeated and the PTE will 00107 // again be checked for write access and copy-on-write 00108 // access. The PTE could still be copy-on-write even 00109 // after the pager is called if the page table page 00110 // was removed from the working set at this time (unlikely, 00111 // but still possible). 00112 // 00113 00114 if (!NT_SUCCESS (MmAccessFault (TRUE, 00115 Address, 00116 UserMode))) { 00117 00118 // 00119 // Raise an access violation status. 00120 // 00121 00122 ExRaiseStatus(STATUS_ACCESS_VIOLATION); 00123 00124 } 00125 } else { 00126 00127 // 00128 // Raise an access violation status. 00129 // 00130 00131 ExRaiseStatus(STATUS_ACCESS_VIOLATION); 00132 00133 } 00134 } 00135 PointerPte += 1; 00136 Address = (PVOID)((ULONG)Address + PAGE_SIZE); 00137 } 00138 } }

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