Correct mprotect page boundries to round up end page. Fixes PR30905.

[asbirlea]

Summary

Update the boundries for mprotect.
Patch by Andrew Adams. Fixes PR30905.

[loladiro]

Yes, this is clearly a bug. LGTM. Though looking back at it, perhaps the rounding to page size should happen in the caller of protectMappedMemory rather than in that function itself, but that's independent of the bug fix.

[chandlerc]

Slight tweak here...

lib/Support/Unix/Memory.inc

158–161

Instead of this, I would use alignAddr. It seems much easier to get correct:

void *Start = alignAddr(M.Address - PageSize + 1, PageSize);
void *End = alignAddr(M.Address + M.Size, PageSize);

[asbirlea]

Address comment.

[asbirlea]

Tested. I'll land in a couple of hours if there are no additional comments. Thanks Keno, Chandler and Andrew.

lib/Support/Unix/Memory.inc

Memory::protectMappedMemory(const MemoryBlock &M, unsigned Flags) {
   if (M.Address == nullptr || M.Size == 0)
     return std::error_code();
 
   if (!Flags)
     return std::error_code(EINVAL, std::generic_category());
 
   int Protect = getPosixProtectionFlags(Flags);
 
-  int Result = ::mprotect((void*)((uintptr_t)M.Address & ~(PageSize-1)), PageSize*((M.Size+PageSize-1)/PageSize), Protect);
+  uintptr_t start = (uintptr_t)M.Address;
+  uintptr_t end = start + M.Size;
+  // Round down the start address to a page boundary
+  start = start & ~(PageSize - 1);
+  // Round up the end address to a page boundary
+  end = (end + PageSize - 1) & ~(PageSize - 1);
+  int Result = ::mprotect((void*)start, end - start, Protect);
+
   if (Result != 0)
     return std::error_code(errno, std::generic_category());
 
   if (Flags & MF_EXEC)
     Memory::InvalidateInstructionCache(M.Address, M.Size);
 
   return std::error_code();
 }