[PATCH v2] linux-user: Adjust pgd_find_hole_fallback result with guest_loaddr

[Ivan A. Melnikov]

While pgd_find_hole_fallback returns the beginning of the
hole found, pgb_find_hole returns guest_base, which
is somewhat different as the binary qemu-user is loading
usually have non-zero load address.

Failing to take that into account leads to random crashes
if the hole is "just big enough", but not bigger:
in that case, important mappings (e.g. parts of qemu-user
itself) may be replaced with the binary we are loading
(e.g. guest elf interpreter).

Downstream issue (in Russian): https://bugzilla.altlinux.org/39141
Signed-off-by: Ivan A. Melnikov <iv@altlinux.org>
---
 linux-user/elfload.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index bab4237e90..58281e00f8 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -2259,7 +2259,8 @@ static uintptr_t pgb_find_hole(uintptr_t guest_loaddr, 
uintptr_t guest_size,
     brk = (uintptr_t)sbrk(0);
 
     if (!maps) {
-        return pgd_find_hole_fallback(guest_size, brk, align, offset);
+        ret = pgd_find_hole_fallback(guest_size, brk, align, offset);
+        return (ret == (uintptr_t) -1) ? -1 : (ret - guest_loaddr);
     }
 
     /* The first hole is before the first map entry. */
-- 
2.29.2