Add NetBSD PaX MPROTECT support in allocateMappedMemory

[krytarowski]

Summary

A user of the Memory::allocateMappedMemory interface
can allocate memory and request additional permission
bits in future. This breaks PaX MPROTECT model on NetBSD,
as these bits have to be reserved with PROT_MPROTECT().

This has been caught by unittests/Support/MemoryTest
and EnabledWrite tests.

This patch fixes these failures and does not introduce
regressions.

Sponsored by <The NetBSD Foundation>

[joerg]

While more localized, this seems to be an even greater hack than adopting the JIT users to use AllocateRWXMemory.

[krytarowski]

The following code triggers failure specific to NetBSD:

$ cat mprotect.c                                                                                                               
#include <sys/types.h>
#include <sys/mman.h>
#include <errno.h>
#include <stdio.h>

int
main(int argc, char **argv)
{
	void *p = mmap(0, 0x1000, PROT_READ, MAP_PRIVATE | MAP_ANON, -1, 0);
	int ret = mprotect(p, 0x1000, PROT_READ | PROT_WRITE);

	printf("ret=%d errno=%d\n", ret, errno);

	return 0;
}
$ ./a.out                                                                                                                      
ret=-1 errno=13

[krytarowski]

@lhames FYI.

Closing this, this should be solved differently, hopefully by refactoring the interface.

lib/Support/Unix/Memory.inc

#ifdef MAP_ANONYMOUS
   MAP_ANONYMOUS
 #else
   MAP_ANON
 #endif
   ; // Ends statement above
 
   int Protect = getPosixProtectionFlags(PFlags);
 
+#if defined(__NetBSD__) && defined(PROT_MPROTECT)
+  // This is required in order to grant additional protection bits
+  Protect |= PROT_MPROTECT(PROT_READ | PROT_WRITE | PROT_EXEC);
+#endif
+
   // Use any near hint and the page size to set a page-aligned starting address
   uintptr_t Start = NearBlock ? reinterpret_cast<uintptr_t>(NearBlock->base()) +
                                       NearBlock->size() : 0;
   if (Start && Start % PageSize)
     Start += PageSize - Start % PageSize;
 
   void *Addr = ::mmap(reinterpret_cast<void*>(Start), PageSize*NumPages,
                       Protect, MMFlags, fd, 0);