linux-user: check valid address in access_ok()

linux-user: check valid address in access_ok()

Fix a crash with LTP testsuite and aarch64:

  tst_test.c:1015: INFO: Timeout per run is 0h 05m 00s
  qemu-aarch64: .../qemu/accel/tcg/translate-all.c:2522: page_check_range: Assertion `start < ((target_ulong)1 << L1_MAP_ADDR_SPACE_BITS)' failed.
  qemu:handle_cpu_signal received signal outside vCPU context @ pc=0x60001554

page_check_range() should never be called with address outside the guest
address space. This patch adds a guest_addr_valid() check in access_ok()
to only call page_check_range() with a valid address.

Fixes: f6768aa1b4c6 ("target/arm: fix AArch64 virtual address space size")
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Message-Id: <20190704084115.24713-1-lvivier@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>