[PATCH] linux-user/mmap: Avoid asserts for out of range mremap calls

[Richard Purdie <richard.purdie@linuxfoundation.org>]

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 
it (and GUEST_ADDR_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 bug I was seeing locally now gives the same behaviour 
regardless of whether reserved_va is set or not.

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;
     }