If mremap() is called without the MREMAP_MAYMOVE flag with a start address
just before the end of memory (reserved_va) where new_size would exceed 
GUEST_ADD_MAX, the assert(end - 1 <= GUEST_ADDR_MAX) in page_set_flags() 
would trigger.

Add an extra guard to the guest_range_valid() checks to prevent this and
avoid asserting binaries when reserved_va is set.

This meant a test case now gives the same behaviour regardless of whether
reserved_va is set or not.

Upstream-Status: Backport [https://github.com/qemu/qemu/commit/ccc5ccc17f8cfbfd87d9aede5d12a2d47c56e712]
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org

Index: qemu-5.2.0/linux-user/mmap.c
===================================================================
--- qemu-5.2.0.orig/linux-user/mmap.c
+++ qemu-5.2.0/linux-user/mmap.c
@@ -727,7 +727,9 @@ abi_long target_mremap(abi_ulong old_add
 
     if (!guest_range_valid(old_addr, old_size) ||
         ((flags & MREMAP_FIXED) &&
-         !guest_range_valid(new_addr, new_size))) {
+         !guest_range_valid(new_addr, new_size)) ||
+        ((flags & MREMAP_MAYMOVE) == 0 &&
+         !guest_range_valid(old_addr, new_size))) {
         errno = ENOMEM;
         return -1;
     }