VirtualProtect bug?

[Robert Reif]

I'm trying to write a test that checks for data overruns
using VirtualAlloc and VirtualProtect and I think
I may have found a bug.  Here is the problem:

DWORD dwPageSize;
BYTE * twoPages, temp;
DWORD flOldProtect;
twoPages = VirtualAlloc(NULL, 2 * dwPageSize, MEM_RESERVE | MEM_COMMIT, 
PAGE_READWRITE);
res = VirtualProtect(twoPages + dwPageSize, dwPageSize, PAGE_NOACCESS, 
&flOldProtect);
temp = twoPages[dwPageSize + 1];    // should cause exception but 
doesn't in wine
twoPages[dwPageSize + 1] = 0;        // does cause exception

I would like to write a test to check the exception handling
but I don't know how to do a __try and __except in C.

Any ideas?

[Robert Reif]

Here is an answer to my own question.

How will this cross compile?

Robert Reif wrote:
> I'm trying to write a test that checks for data overruns
> using VirtualAlloc and VirtualProtect and I think
> I may have found a bug.  Here is the problem:
>
> DWORD dwPageSize;
> BYTE * twoPages, temp;
> DWORD flOldProtect;
> twoPages = VirtualAlloc(NULL, 2 * dwPageSize, MEM_RESERVE | 
> MEM_COMMIT, PAGE_READWRITE);
> res = VirtualProtect(twoPages + dwPageSize, dwPageSize, PAGE_NOACCESS, 
> &flOldProtect);
> temp = twoPages[dwPageSize + 1];    // should cause exception but 
> doesn't in wine
> twoPages[dwPageSize + 1] = 0;        // does cause exception
>
> I would like to write a test to check the exception handling
> but I don't know how to do a __try and __except in C.
>
> Any ideas?

Index: dlls/kernel/tests/virtual.c
===================================================================
RCS file: /home/wine/wine/dlls/kernel/tests/virtual.c,v
retrieving revision 1.2
diff -u -r1.2 virtual.c
--- dlls/kernel/tests/virtual.c	10 Feb 2004 20:07:56 -0000	1.2
+++ dlls/kernel/tests/virtual.c	16 May 2004 01:28:00 -0000
@@ -24,6 +24,54 @@
 #include "winbase.h"
 #include "winerror.h"
 #include "wine/test.h"
+#include "excpt.h"
+#include "wine/exception.h"
+
+static WINE_EXCEPTION_FILTER(page_fault)
+{
+    if (GetExceptionCode() == EXCEPTION_ACCESS_VIOLATION ||
+        GetExceptionCode() == EXCEPTION_PRIV_INSTRUCTION)
+        return EXCEPTION_EXECUTE_HANDLER;
+    return EXCEPTION_CONTINUE_SEARCH;
+}
+
+static void test_VirtualProtect()
+{
+    DWORD dwPageSize;
+    BYTE * twoPages, temp;
+    DWORD old_prot;
+    SYSTEM_INFO sSysInfo;
+    BOOL res;
+
+    GetSystemInfo(&sSysInfo);
+    dwPageSize = sSysInfo.dwPageSize;
+
+    twoPages = VirtualAlloc(0, 2 * dwPageSize, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
+    ok(twoPages!=NULL,"Failed to allocate two pages\n");
+    if (twoPages==NULL)
+        return;
+
+    res = VirtualProtect(twoPages + dwPageSize, dwPageSize, PAGE_NOACCESS, &old_prot);
+    ok(res,"Failed to set protection for second page\n");
+    if (!res)
+        return;
+
+    __TRY {
+        temp = twoPages[dwPageSize];
+        ok(FALSE,"didn't get fault reading from page with PAGE_NOACCESS\n");
+    } __EXCEPT(page_fault) {
+        ok(TRUE,"got fault\n");
+    } __ENDTRY
+
+    __TRY {
+        twoPages[dwPageSize] = 0;
+        ok(FALSE,"didn't get fault writing to page with PAGE_NOACCESS\n");
+    } __EXCEPT(page_fault) {
+        ok(TRUE,"got fault\n");
+    } __ENDTRY
+
+    ok(VirtualFree(twoPages, 0, MEM_RELEASE), "VirtualFree failed\n");
+}

static void test_VirtualAlloc(void)
 {
@@ -110,4 +158,5 @@
 START_TEST(virtual)
 {
     test_VirtualAlloc();
+    test_VirtualProtect();
 }

[Alexandre Julliard]

Robert Reif  writes:
> I'm trying to write a test that checks for data overruns
> using VirtualAlloc and VirtualProtect and I think
> I may have found a bug.  Here is the problem:
>
> DWORD dwPageSize;
> BYTE * twoPages, temp;
> DWORD flOldProtect;
> twoPages = VirtualAlloc(NULL, 2 * dwPageSize, MEM_RESERVE |
> MEM_COMMIT, PAGE_READWRITE);
> res = VirtualProtect(twoPages + dwPageSize, dwPageSize, PAGE_NOACCESS,
> &flOldProtect);
> temp = twoPages[dwPageSize + 1];    // should cause exception but
> doesn't in wine
> twoPages[dwPageSize + 1] = 0;        // does cause exception

Most likely the read access was optimized out. Try doing the access
through a volatile pointer.