[msan] Check for pvalloc overflow

[cryptoad]

Summary

CheckForPvallocOverflow was introduced with D35818 to detect when pvalloc
would wrap when rounding up to the next multiple of the page size.

Add this check to MSan's pvalloc implementation.

[cryptoad]

Correcting Monday morning brain fart.

lib/msan/msan_allocator.cc

 }
 
 void *msan_valloc(uptr size, StackTrace *stack) {
   return SetErrnoOnNull(MsanAllocate(stack, size, GetPageSizeCached(), false));
 }
 
 void *msan_pvalloc(uptr size, StackTrace *stack) {
   uptr PageSize = GetPageSizeCached();
+  if (UNLIKELY(CheckForPvallocOverflow(size, PageSize))) {
+    errno = errno_ENOMEM;
+    return Allocator::FailureHandler::OnBadRequest();
+  }
   // pvalloc(0) should allocate one page.
-  size = size == 0 ? PageSize : RoundUpTo(size, PageSize);
+  size = size ? RoundUpTo(size, PageSize) : PageSize;
   return SetErrnoOnNull(MsanAllocate(stack, size, PageSize, false));
 }
 
 void *msan_aligned_alloc(uptr alignment, uptr size, StackTrace *stack) {
   if (UNLIKELY(!CheckAlignedAllocAlignmentAndSize(alignment, size))) {
     errno = errno_EINVAL;
     return Allocator::FailureHandler::OnBadRequest();
   }

lib/msan/tests/msan_test.cc

TEST(MemorySanitizer, pvalloc) {
   EXPECT_EQ(0U, (uintptr_t)p % PageSize);
   EXPECT_EQ(2 * PageSize, __sanitizer_get_allocated_size(p));
   free(p);
 
   p = pvalloc(0);  // pvalloc(0) should allocate at least one page.
   EXPECT_EQ(0U, (uintptr_t)p % PageSize);
   EXPECT_EQ(PageSize, __sanitizer_get_allocated_size(p));
   free(p);
+
+  // Overflows in pvalloc should be caught.
+  errno = 0;
+  p = pvalloc((uintptr_t)-PageSize);
+  EXPECT_EQ(p, nullptr);
+  EXPECT_EQ(errno, ENOMEM);
+
+  errno = 0;
+  p = pvalloc((uintptr_t)-1);
+  EXPECT_EQ(p, nullptr);
+  EXPECT_EQ(errno, ENOMEM);
 }
 #endif
 
 TEST(MemorySanitizer, inet_pton) {
   const char *s = "1:0:0:0:0:0:0:8";
   unsigned char buf[sizeof(struct in6_addr)];
   int res = inet_pton(AF_INET6, s, buf);
   ASSERT_EQ(1, res);