[PATCH] softmmu: Always initialize xlat in address_space_translate_for_iotlb

[Richard Henderson]

The bug is an uninitialized memory read, along the translate_fail
path, which results in garbage being read from iotlb_to_section,
which can lead to a crash in io_readx/io_writex.

The bug may be fixed by writing any value with zero
in ~TARGET_PAGE_MASK, so that the call to iotlb_to_section using
the xlat'ed address returns io_mem_unassigned, as desired by the
translate_fail path.

It is most useful to record the original physical page address,
which will eventually be logged by memory_region_access_valid
when the access is rejected by unassigned_mem_accepts.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1065
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 softmmu/physmem.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 657841eed0..fb0f0709b5 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -681,6 +681,9 @@ address_space_translate_for_iotlb(CPUState *cpu, int asidx, 
hwaddr addr,
     AddressSpaceDispatch *d =
         qatomic_rcu_read(&cpu->cpu_ases[asidx].memory_dispatch);
 
+    /* Record the original phys page for use by the translate_fail path. */
+    *xlat = addr;
+
     for (;;) {
         section = address_space_translate_internal(d, addr, &addr, plen, 
false);
 
-- 
2.34.1