s390x/css: handle cssid 255 correctly
The cssid 255 is reserved but still valid from an architectural
point of view. However, feeding a bogus schid of 0xffffffff into
the virtio hypercall will lead to a crash:
Stack trace of thread 138363:
#0 0x00000000100d168c css_find_subch (qemu-system-s390x)
#1 0x00000000100d3290 virtio_ccw_hcall_notify
#2 0x00000000100cbf60 s390_virtio_hypercall
#3 0x000000001010ff7a handle_hypercall
#4 0x0000000010079ed4 kvm_cpu_exec (qemu-system-s390x)
#5 0x00000000100609b4 qemu_kvm_cpu_thread_fn
#6 0x000003ff8b887bb4 start_thread (libpthread.so.0)
#7 0x000003ff8b78df0a thread_start (libc.so.6)
This is because the css array was only allocated for 0..254
instead of 0..255.
Let's fix this by bumping MAX_CSSID to 255 and fencing off the
reserved cssid of 255 during css image allocation.
Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
(cherry picked from commit 882b3b97697affb36ca3d174f42f846232008979)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index 3a1d919..0eb53f9 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -139,7 +139,8 @@
int css_create_css_image(uint8_t cssid, bool default_image)
{
trace_css_new_image(cssid, default_image ? "(default)" : "");
- if (cssid > MAX_CSSID) {
+ /* 255 is reserved */
+ if (cssid == 255) {
return -EINVAL;
}
if (channel_subsys.css[cssid]) {
@@ -1226,7 +1227,7 @@
uint8_t real_cssid;
real_cssid = (!m && (cssid == 0)) ? channel_subsys.default_cssid : cssid;
- if (real_cssid > MAX_CSSID || ssid > MAX_SSID ||
+ if (ssid > MAX_SSID ||
!channel_subsys.css[real_cssid] ||
!channel_subsys.css[real_cssid]->sch_set[ssid]) {
return true;
@@ -1241,9 +1242,6 @@
CssImage *css;
trace_css_chpid_add(cssid, chpid, type);
- if (cssid > MAX_CSSID) {
- return -EINVAL;
- }
css = channel_subsys.css[cssid];
if (!css) {
return -EINVAL;
diff --git a/hw/s390x/css.h b/hw/s390x/css.h
index a320eea..fdcfa3a 100644
--- a/hw/s390x/css.h
+++ b/hw/s390x/css.h
@@ -19,7 +19,7 @@
/* Channel subsystem constants. */
#define MAX_SCHID 65535
#define MAX_SSID 3
-#define MAX_CSSID 254 /* 255 is reserved */
+#define MAX_CSSID 255
#define MAX_CHPID 255
#define MAX_CIWS 62