Add OS::system_page_size

2 files changed, 25 insertions, 4 deletions

diff --git a/src/lib/utils/os_utils.cpp b/src/lib/utils/os_utils.cpp
index 769615543..f2813b323 100644
--- a/src/lib/utils/os_utils.cpp
+++ b/src/lib/utils/os_utils.cpp
@@ -197,6 +197,24 @@ uint64_t OS::get_system_timestamp_ns()
    return std::chrono::duration_cast<std::chrono::nanoseconds>(now).count();
    }
 
+size_t OS::system_page_size()
+   {
+#if defined(BOTAN_TARGET_OS_HAS_POSIX1)
+   long p = ::sysconf(_SC_PAGESIZE);
+   if(p > 1)
+      return static_cast<size_t>(p);
+   else
+      return 4096;
+#elif defined(BOTAN_TARGET_OS_HAS_VIRTUAL_LOCK)
+   SYSTEM_INFO sys_info;
+   ::GetSystemInfo(&sys_info);
+   return sys_info.dwPageSize;
+#endif
+
+   // default value
+   return 4096;
+   }
+
 size_t OS::get_memory_locking_limit()
    {
 #if defined(BOTAN_TARGET_OS_HAS_POSIX1)
@@ -255,16 +273,13 @@ size_t OS::get_memory_locking_limit()
       return 0;
       }
 
-   SYSTEM_INFO sSysInfo;
-   ::GetSystemInfo(&sSysInfo);
-
    // According to Microsoft MSDN:
    // The maximum number of pages that a process can lock is equal to the number of pages in its minimum working set minus a small overhead
    // In the book "Windows Internals Part 2": the maximum lockable pages are minimum working set size - 8 pages 
    // But the information in the book seems to be inaccurate/outdated
    // I've tested this on Windows 8.1 x64, Windows 10 x64 and Windows 7 x86
    // On all three OS the value is 11 instead of 8
-   size_t overhead = sSysInfo.dwPageSize * 11ULL;
+   size_t overhead = OS::system_page_size() * 11ULL;
    if(working_min > overhead)
       {
       size_t lockable_bytes = working_min - overhead;
diff --git a/src/lib/utils/os_utils.h b/src/lib/utils/os_utils.h
index feccdbe73..5210b2523 100644
--- a/src/lib/utils/os_utils.h
+++ b/src/lib/utils/os_utils.h
@@ -68,6 +68,12 @@ uint64_t BOTAN_TEST_API get_system_timestamp_ns();
 size_t get_memory_locking_limit();
 
 /**
+* Return the size of a memory page, if that can be derived on the
+* current system. Otherwise returns some default value (eg 4096)
+*/
+size_t system_page_size();
+
+/**
 * Request so many bytes of page-aligned RAM locked into memory using
 * mlock, VirtualLock, or similar. Returns null on failure. The memory
 * returned is zeroed. Free it with free_locked_pages.