From: Mark Cave-Ayland <[email protected]>
Currently when portio_list MemoryRegions are freed using portio_list_destroy()
the RCU
thread segfaults generating a backtrace similar to that below:
#0 0x5555599a34b6 in phys_section_destroy ../softmmu/physmem.c:996
#1 0x5555599a37a3 in phys_sections_free ../softmmu/physmem.c:1011
#2 0x5555599b24aa in address_space_dispatch_free ../softmmu/physmem.c:2430
#3 0x55555996a283 in flatview_destroy ../softmmu/memory.c:292
#4 0x55555a2cb9fb in call_rcu_thread ../util/rcu.c:284
#5 0x55555a29b71d in qemu_thread_start ../util/qemu-thread-posix.c:541
#6 0x7ffff4a0cea6 in start_thread nptl/pthread_create.c:477
#7 0x7ffff492ca2e in __clone (/lib/x86_64-linux-gnu/libc.so.6+0xfca2e)
The problem here is that portio_list_destroy() unparents the portio_list
MemoryRegions causing them to be freed immediately, however the flatview
still has a reference to the MemoryRegion and so causes a use-after-free
segfault when the RCU thread next updates the flatview.
Solve the lifetime issue by making MemoryRegionPortioList the owner of the
portio_list MemoryRegions, and then reparenting them to the portio_list
owner. This ensures that they can be accessed as QOM children via the
portio_list owner, yet the MemoryRegionPortioList owns the refcount.
Update portio_list_destroy() to unparent the MemoryRegion from the
portio_list owner (while keeping mrpio->mr live until finalization of the
MemoryRegionPortioList), so that the portio_list MemoryRegions remain
allocated until flatview_destroy() removes the final refcount upon the
next flatview update.
Signed-off-by: Mark Cave-Ayland <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
---
softmmu/ioport.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/softmmu/ioport.c b/softmmu/ioport.c
index 33720fe5664a..b66e0a5a8ebc 100644
--- a/softmmu/ioport.c
+++ b/softmmu/ioport.c
@@ -229,6 +229,8 @@ static void portio_list_add_1(PortioList *piolist,
unsigned off_low, unsigned off_high)
{
MemoryRegionPortioList *mrpio;
+ Object *owner;
+ char *name;
unsigned i;
/* Copy the sub-list and null-terminate it. */
@@ -245,8 +247,25 @@ static void portio_list_add_1(PortioList *piolist,
mrpio->ports[i].base = start + off_low;
}
- memory_region_init_io(&mrpio->mr, piolist->owner, &portio_ops, mrpio,
+ /*
+ * The MemoryRegion owner is the MemoryRegionPortioList since that manages
+ * the lifecycle via the refcount
+ */
+ memory_region_init_io(&mrpio->mr, OBJECT(mrpio), &portio_ops, mrpio,
piolist->name, off_high - off_low);
+
+ /* Reparent the MemoryRegion to the piolist owner */
+ object_ref(&mrpio->mr);
+ object_unparent(OBJECT(&mrpio->mr));
+ if (!piolist->owner) {
+ owner = container_get(qdev_get_machine(), "/unattached");
+ } else {
+ owner = piolist->owner;
+ }
+ name = g_strdup_printf("%s[*]", piolist->name);
+ object_property_add_child(owner, name, OBJECT(&mrpio->mr));
+ g_free(name);
+
if (piolist->flush_coalesced_mmio) {
memory_region_set_flush_coalesced(&mrpio->mr);
}
@@ -308,6 +327,7 @@ static void memory_region_portio_list_finalize(Object *obj)
{
MemoryRegionPortioList *mrpio = MEMORY_REGION_PORTIO_LIST(obj);
+ object_unref(&mrpio->mr);
g_free(mrpio->ports);
}
--
2.40.1
