Enable large pages in Windows programmatically - c

Question

I want to use large pages in my app like this:
VirtualAlloc(NULL, n_bytes, MEM_RESERVE | MEM_COMMIT | MEM_LARGE_PAGES, PAGE_READWRITE, PAGE_READWRITE);
I plan to enable large pages for the current user during installation, while having elevated admin rights. Does anyone have code for enabling large pages programmatically?

Answer 1

I'm posting what I've gathered.
The general idea:
Enable large pages for the current user account. (Requires admin rights).
Enable large pages for the current process token. (Requires admin rights).
Allocate the memory (granular to large page size, 2Mb, in fact).
If you have UAC properly disabled, you need to execute step 1 only once with admin rights. If you have UAC enabled, you always have to execute it all with admin rights.
#define UNICODE
#define _UNICODE
#include <windows.h>
#include <ntsecapi.h>
#include <ntstatus.h>
#include <Sddl.h>
void InitLsaString(PLSA_UNICODE_STRING LsaString, LPWSTR String)
{
DWORD StringLength;
if (String == NULL) {
LsaString->Buffer = NULL;
LsaString->Length = 0;
LsaString->MaximumLength = 0;
return;
}
StringLength = wcslen(String);
LsaString->Buffer = String;
LsaString->Length = (USHORT)StringLength * sizeof(WCHAR);
LsaString->MaximumLength = (USHORT)(StringLength + 1) * sizeof(WCHAR);
}
NTSTATUS OpenPolicy(LPWSTR ServerName, DWORD DesiredAccess, PLSA_HANDLE PolicyHandle)
{
LSA_OBJECT_ATTRIBUTES ObjectAttributes;
LSA_UNICODE_STRING ServerString;
PLSA_UNICODE_STRING Server = NULL;
//
// Always initialize the object attributes to all zeroes.
//
ZeroMemory(&ObjectAttributes, sizeof(ObjectAttributes));
if (ServerName != NULL) {
//
// Make a LSA_UNICODE_STRING out of the LPWSTR passed in
//
InitLsaString(&ServerString, ServerName);
Server = &ServerString;
}
//
// Attempt to open the policy.
//
return LsaOpenPolicy(
Server,
&ObjectAttributes,
DesiredAccess,
PolicyHandle
);
}
NTSTATUS SetPrivilegeOnAccount(LSA_HANDLE PolicyHandle, PSID AccountSid, LPWSTR PrivilegeName, BOOL bEnable)
{
LSA_UNICODE_STRING PrivilegeString;
//
// Create a LSA_UNICODE_STRING for the privilege name.
//
InitLsaString(&PrivilegeString, PrivilegeName);
//
// grant or revoke the privilege, accordingly
//
if (bEnable) {
return LsaAddAccountRights(
PolicyHandle, // open policy handle
AccountSid, // target SID
&PrivilegeString, // privileges
1 // privilege count
);
}
else {
return LsaRemoveAccountRights(
PolicyHandle, // open policy handle
AccountSid, // target SID
FALSE, // do not disable all rights
&PrivilegeString, // privileges
1 // privilege count
);
}
}
void main()
{
HANDLE hToken = NULL;
if (!OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, &hToken))
{
applog(LOG_INFO, "OpenProcessToken failed. GetLastError returned: %d\n", GetLastError());
return -1;
}
DWORD dwBufferSize = 0;
// Probe the buffer size reqired for PTOKEN_USER structure
if (!GetTokenInformation(hToken, TokenUser, NULL, 0, &dwBufferSize) &&
(GetLastError() != ERROR_INSUFFICIENT_BUFFER))
{
applog(LOG_INFO, "GetTokenInformation failed. GetLastError returned: %d\n", GetLastError());
// Cleanup
CloseHandle(hToken);
hToken = NULL;
return -1;
}
PTOKEN_USER pTokenUser = (PTOKEN_USER) malloc(dwBufferSize);
// Retrieve the token information in a TOKEN_USER structure
if (!GetTokenInformation(
hToken,
TokenUser,
pTokenUser,
dwBufferSize,
&dwBufferSize))
{
applog(LOG_INFO, "GetTokenInformation failed. GetLastError returned: %d\n", GetLastError());
// Cleanup
CloseHandle(hToken);
hToken = NULL;
return -1;
}
// Print SID string
LPWSTR strsid;
ConvertSidToStringSid(pTokenUser->User.Sid, &strsid);
applog(LOG_INFO, "User SID: %S\n", strsid);
// Cleanup
CloseHandle(hToken);
hToken = NULL;
NTSTATUS status;
LSA_HANDLE policyHandle;
if (status = OpenPolicy(NULL, POLICY_CREATE_ACCOUNT | POLICY_LOOKUP_NAMES, &policyHandle))
{
applog(LOG_INFO, "OpenPolicy %d", status);
}
// Add new privelege to the account
if (status = SetPrivilegeOnAccount(policyHandle, pTokenUser->User.Sid, SE_LOCK_MEMORY_NAME, TRUE))
{
applog(LOG_INFO, "OpenPSetPrivilegeOnAccountolicy %d", status);
}
// Enable this priveledge for the current process
hToken = NULL;
TOKEN_PRIVILEGES tp;
if (!OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY | TOKEN_ADJUST_PRIVILEGES, &hToken))
{
applog(LOG_INFO, "OpenProcessToken #2 failed. GetLastError returned: %d\n", GetLastError());
return -1;
}
tp.PrivilegeCount = 1;
tp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
if (!LookupPrivilegeValue(NULL, SE_LOCK_MEMORY_NAME, &tp.Privileges[0].Luid))
{
applog(LOG_INFO, "LookupPrivilegeValue failed. GetLastError returned: %d\n", GetLastError());
return -1;
}
BOOL result = AdjustTokenPrivileges(hToken, FALSE, &tp, 0, (PTOKEN_PRIVILEGES)NULL, 0);
DWORD error = GetLastError();
if (!result || (error != ERROR_SUCCESS))
{
applog(LOG_INFO, "AdjustTokenPrivileges failed. GetLastError returned: %d\n", error);
return -1;
}
// Cleanup
CloseHandle(hToken);
hToken = NULL;
SIZE_T pageSize = GetLargePageMinimum();
// Finally allocate the memory
char *largeBuffer = VirtualAlloc(NULL, pageSize * N_PAGES_TO_ALLOC, MEM_RESERVE | MEM_COMMIT | MEM_LARGE_PAGES, PAGE_READWRITE);
if (largeBuffer)
{
applog(LOG_INFO, "VirtualAlloc failed, error 0x%x", GetLastError());
}
}