xen/hypercall: fix hypercall fallback code for very old hypervisors

While copying the argument structures in HYPERVISOR_event_channel_op()
and HYPERVISOR_physdev_op() into the local variable is sufficiently
safe even if the actual structure is smaller than the container one,
copying back eventual output values the same way isn't: This may
collide with on-stack variables (particularly "rc") which may change
between the first and second memcpy() (i.e. the second memcpy() could
discard that change).

Move the fallback code into out-of-line functions, and handle all of
the operations known by this old a hypervisor individually: Some don't
require copying back anything at all, and for the rest use the
individual argument structures' sizes rather than the container's.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
[v2: Reduce #define/#undef usage in HYPERVISOR_physdev_op_compat().]
[v3: Fix compile errors when modules use said hypercalls]
[v4: Add xen_ prefix to the HYPERCALL_..]
[v5: Alter the name and only EXPORT_SYMBOL_GPL one of them]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 80 insertions, 0 deletions

diff --git a/drivers/xen/fallback.c b/drivers/xen/fallback.c
new file mode 100644
index 000000000000..0ef7c4d40f86
--- /dev/null
+++ b/drivers/xen/fallback.c
@@ -0,0 +1,80 @@
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/bug.h>
+#include <linux/export.h>
+#include <asm/hypervisor.h>
+#include <asm/xen/hypercall.h>
+
+int xen_event_channel_op_compat(int cmd, void *arg)
+{
+        struct evtchn_op op;
+        int rc;
+
+        op.cmd = cmd;
+        memcpy(&op.u, arg, sizeof(op.u));
+        rc = _hypercall1(int, event_channel_op_compat, &op);
+
+        switch (cmd) {
+        case EVTCHNOP_close:
+        case EVTCHNOP_send:
+        case EVTCHNOP_bind_vcpu:
+        case EVTCHNOP_unmask:
+                /* no output */
+                break;
+
+#define COPY_BACK(eop) \
+        case EVTCHNOP_##eop: \
+                memcpy(arg, &op.u.eop, sizeof(op.u.eop)); \
+                break
+
+        COPY_BACK(bind_interdomain);
+        COPY_BACK(bind_virq);
+        COPY_BACK(bind_pirq);
+        COPY_BACK(status);
+        COPY_BACK(alloc_unbound);
+        COPY_BACK(bind_ipi);
+#undef COPY_BACK
+
+        default:
+                WARN_ON(rc != -ENOSYS);
+                break;
+        }
+
+        return rc;
+}
+EXPORT_SYMBOL_GPL(xen_event_channel_op_compat);
+
+int HYPERVISOR_physdev_op_compat(int cmd, void *arg)
+{
+        struct physdev_op op;
+        int rc;
+
+        op.cmd = cmd;
+        memcpy(&op.u, arg, sizeof(op.u));
+        rc = _hypercall1(int, physdev_op_compat, &op);
+
+        switch (cmd) {
+        case PHYSDEVOP_IRQ_UNMASK_NOTIFY:
+        case PHYSDEVOP_set_iopl:
+        case PHYSDEVOP_set_iobitmap:
+        case PHYSDEVOP_apic_write:
+                /* no output */
+                break;
+
+#define COPY_BACK(pop, fld) \
+        case PHYSDEVOP_##pop: \
+                memcpy(arg, &op.u.fld, sizeof(op.u.fld)); \
+                break
+
+        COPY_BACK(irq_status_query, irq_status_query);
+        COPY_BACK(apic_read, apic_op);
+        COPY_BACK(ASSIGN_VECTOR, irq_op);
+#undef COPY_BACK
+
+        default:
+                WARN_ON(rc != -ENOSYS);
+                break;
+        }
+
+        return rc;
+}