aboutsummaryrefslogtreecommitdiff
path: root/winsup/cygwin/hookapi.cc
blob: a58814e6bbd3309ef8569875b421ca9d7c06decb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
#include "winsup.h"
#include "cygerrno.h"
#include "security.h"
#include "path.h"
#include "fhandler.h"
#include "dtable.h"
#include "cygheap.h"
#include <stdlib.h>
#include <imagehlp.h>
#include <alloca.h>

#define rva(coerce, base, addr) (coerce) ((char *) (base) + (addr))
#define rvacyg(coerce, addr) rva (coerce, cygwin_hmodule, addr)

struct function_hook
{
  const char *name;	// Function name, e.g. "DirectDrawCreateEx".
  const void *hookfn;	// Address of your function.
  void *origfn;		// Stored by HookAPICalls, the address of the original function.
};

/* Given an HMODULE, returns a pointer to the PE header */
static PIMAGE_NT_HEADERS
PEHeaderFromHModule (HMODULE hModule)
{
  PIMAGE_NT_HEADERS pNTHeader;

  if (PIMAGE_DOS_HEADER(hModule) ->e_magic != IMAGE_DOS_SIGNATURE)
    pNTHeader = NULL;
  else
    {
      pNTHeader = PIMAGE_NT_HEADERS (PBYTE (hModule)
				     + PIMAGE_DOS_HEADER (hModule) ->e_lfanew);
      if (pNTHeader->Signature != IMAGE_NT_SIGNATURE)
	pNTHeader = NULL;
    }

  return pNTHeader;
}

long
rvadelta (PIMAGE_NT_HEADERS pnt, DWORD import_rva)
{
  PIMAGE_SECTION_HEADER section = (PIMAGE_SECTION_HEADER) (pnt + 1);
  for (int i = 0; i < pnt->FileHeader.NumberOfSections; i++)
    if (section[i].VirtualAddress <= import_rva
	&& (section[i].VirtualAddress + section[i].Misc.VirtualSize) >= import_rva)
    // if (strncasematch ((char *) section[i].Name, ".idata", IMAGE_SIZEOF_SHORT_NAME))
      return section[i].VirtualAddress - section[i].PointerToRawData;
  return -1;
}

void *
putmem (PIMAGE_THUNK_DATA pi, const void *hookfn)
{
  DWORD ofl;
  if (!VirtualProtect (pi, sizeof (PVOID), PAGE_READWRITE, &ofl) )
    return NULL;

  void *origfn = (void *) pi->u1.Function;
  pi->u1.Function = (DWORD) hookfn;

  VirtualProtect (pi, sizeof (PVOID), ofl, &ofl);
  return origfn;
}

/* Builds stubs for and redirects the IAT for one DLL (pImportDesc) */

static bool
RedirectIAT (function_hook& fh, PIMAGE_IMPORT_DESCRIPTOR pImportDesc,
	     HMODULE hm)
{
  // If no import names table, we can't redirect this, so bail
  if (pImportDesc->OriginalFirstThunk == 0)
      return false;

  /* import address table */
  PIMAGE_THUNK_DATA pt = rva (PIMAGE_THUNK_DATA, hm, pImportDesc->FirstThunk);
  /* import names table */
  PIMAGE_THUNK_DATA pn = rva (PIMAGE_THUNK_DATA, hm, pImportDesc->OriginalFirstThunk);

  /* Scan through the IAT, completing the stubs and redirecting the IAT
     entries to point to the stubs. */
  for (PIMAGE_THUNK_DATA pi = pt; pn->u1.Ordinal; pi++, pn++)
    {
      if (IMAGE_SNAP_BY_ORDINAL (pn->u1.Ordinal) )
	continue;

      /* import by name */
      PIMAGE_IMPORT_BY_NAME pimp = rva (PIMAGE_IMPORT_BY_NAME, hm, pn->u1.AddressOfData);

      if (strcmp (fh.name, (char *) pimp->Name) == 0)
	{
	  fh.origfn = putmem (pi, fh.hookfn);
	  if (!fh.origfn)
	    return false;
	  hook_chain *hc;
	  for (hc = &cygheap->hooks; hc->next; hc = hc->next)
	    continue;
	  hc->next = (hook_chain *) cmalloc (HEAP_1_HOOK, sizeof (hook_chain));
	  hc->next->loc = (void **) pi;
	  hc->next->func = fh.hookfn;
	  hc->next->next = NULL;
	  break;
      }
  }

  return true;
}

void
get_export (function_hook& fh)
{
  PIMAGE_DOS_HEADER pdh = (PIMAGE_DOS_HEADER) cygwin_hmodule;
  if (pdh->e_magic != IMAGE_DOS_SIGNATURE)
    return;
  PIMAGE_NT_HEADERS pnt = (PIMAGE_NT_HEADERS) ((char *) pdh + pdh->e_lfanew);
  if (pnt->Signature != IMAGE_NT_SIGNATURE || pnt->FileHeader.SizeOfOptionalHeader == 0)
    return;
  PIMAGE_EXPORT_DIRECTORY pexp =
    rvacyg (PIMAGE_EXPORT_DIRECTORY,
	 pnt->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress);
  if (!pexp)
    return;

  PDWORD pfuncs = rvacyg (PDWORD, pexp->AddressOfFunctions);
  PDWORD pnames = rvacyg (PDWORD, pexp->AddressOfNames);
  for (DWORD i = 0; i < pexp->NumberOfNames; i++)
    if (strcmp (fh.name, rvacyg (char *, pnames[i])) == 0)
      {
	fh.origfn = rvacyg (void *, pfuncs[i]);
	break;
      }
}

static const char *
makename (const char *name, char *&buf, int& i, int inc)
{
  i += inc;
  static const char *testers[] = {"NOTUSED", "64", "32"};
  if (i < 0 || i >= (int) (sizeof (testers) / sizeof (testers[0])))
    return NULL;
  if (i)
    {
      __small_sprintf (buf, "_%s%s", name, testers[i]);
      name = buf;
    }
  return name;
}

// Top level routine to find the EXE's imports, and redirect them
void *
hook_or_detect_cygwin (const char *name, const void *fn, WORD& subsys)
{
  HMODULE hm = fn ? GetModuleHandle (NULL) : (HMODULE) name;
  PIMAGE_NT_HEADERS pExeNTHdr = PEHeaderFromHModule (hm);

  if (!pExeNTHdr)
    return false;

  subsys =  pExeNTHdr->OptionalHeader.Subsystem;

  DWORD importRVA = pExeNTHdr->OptionalHeader.DataDirectory
		      [IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress;
  if (!importRVA)
    return false;

  long delta = fn ? 0 : rvadelta (pExeNTHdr, importRVA);
  if (delta < 0)
    return false;

  // Convert imports RVA to a usable pointer
  PIMAGE_IMPORT_DESCRIPTOR pdfirst = rva (PIMAGE_IMPORT_DESCRIPTOR, hm, importRVA - delta);

  function_hook fh;
  fh.origfn = NULL;
  fh.hookfn = fn;
  char *buf = (char *) alloca (strlen (name) + sizeof ("_64"));
  int i;
  // Iterate through each import descriptor, and redirect if appropriate
  for (PIMAGE_IMPORT_DESCRIPTOR pd = pdfirst; pd->FirstThunk; pd++)
    {
      if (!strcasematch (rva (PSTR, hm, pd->Name - delta), "cygwin1.dll"))
	continue;
      if (!fn)
	return (void *) "found it";	// just checking if executable used cygwin1.dll
      i = -1;
      while (!fh.origfn && (fh.name = makename (name, buf, i, 1)))
	RedirectIAT (fh, pd, hm);
      if (fh.origfn)
	break;
    }

  while (!fh.origfn && (fh.name = makename (name, buf, i, -1)))
    get_export (fh);

  return fh.origfn;
}

void
ld_preload ()
{
  char *p = getenv ("LD_PRELOAD");
  if (!p)
    return;
  char *s = (char *) alloca (strlen (p) + 1);
  strcpy (s, p);
  char *here = NULL;
  for (p = strtok_r (s, ":\t\n", &here); p; p = strtok_r (NULL, ":\t\n", &here))
    {
      path_conv lib (p);
      if (!LoadLibrary (lib))
	{
	  __seterrno ();
	  api_fatal ("error while loading shared libraries: %s: "
		     "cannot open shared object file: %s", p,
		     strerror (get_errno ()));
	}
    }
}

void
fixup_hooks_after_fork ()
{
  for (hook_chain *hc = &cygheap->hooks; (hc = hc->next); )
    putmem ((PIMAGE_THUNK_DATA) hc->loc, hc->func);
}