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>

diff --git a/arch/x86/include/asm/xen/hypercall.h b/arch/x86/include/asm/xen/hypercall.h
index 59c226d120cdeccb6d8615e396f65b3ff2d4c050..c20d1ce62dc6a0a236280ab51b7ac8386fb1c32b 100644 (file)
--- a/arch/x86/include/asm/xen/hypercall.h
+++ b/arch/x86/include/asm/xen/hypercall.h
@@ -359,18 +359,14 @@ HYPERVISOR_update_va_mapping(unsigned long va, pte_t new_val,
                return _hypercall4(int, update_va_mapping, va,
                                   new_val.pte, new_val.pte >> 32, flags);
 }
+extern int __must_check xen_event_channel_op_compat(int, void *);
 
 static inline int
 HYPERVISOR_event_channel_op(int cmd, void *arg)
 {
        int rc = _hypercall2(int, event_channel_op, cmd, arg);
-       if (unlikely(rc == -ENOSYS)) {
-               struct evtchn_op op;
-               op.cmd = cmd;
-               memcpy(&op.u, arg, sizeof(op.u));
-               rc = _hypercall1(int, event_channel_op_compat, &op);
-               memcpy(arg, &op.u, sizeof(op.u));
-       }
+       if (unlikely(rc == -ENOSYS))
+               rc = xen_event_channel_op_compat(cmd, arg);
        return rc;
 }
 
@@ -386,17 +382,14 @@ HYPERVISOR_console_io(int cmd, int count, char *str)
        return _hypercall3(int, console_io, cmd, count, str);
 }
 
+extern int __must_check HYPERVISOR_physdev_op_compat(int, void *);
+
 static inline int
 HYPERVISOR_physdev_op(int cmd, void *arg)
 {
        int rc = _hypercall2(int, physdev_op, cmd, arg);
-       if (unlikely(rc == -ENOSYS)) {
-               struct physdev_op op;
-               op.cmd = cmd;
-               memcpy(&op.u, arg, sizeof(op.u));
-               rc = _hypercall1(int, physdev_op_compat, &op);
-               memcpy(arg, &op.u, sizeof(op.u));
-       }
+       if (unlikely(rc == -ENOSYS))
+               rc = HYPERVISOR_physdev_op_compat(cmd, arg);
        return rc;
 }
 

diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 0e86370354572ac7d4116eb70cf6e41d1a52cf35..46de6cdfccb35b8560e57a50babce496754d0bd6 100644 (file)
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -2,7 +2,7 @@ ifneq ($(CONFIG_ARM),y)
 obj-y  += manage.o balloon.o
 obj-$(CONFIG_HOTPLUG_CPU)              += cpu_hotplug.o
 endif
-obj-y  += grant-table.o features.o events.o
+obj-y  += grant-table.o features.o events.o fallback.o
 obj-y  += xenbus/
 
 nostackp := $(call cc-option, -fno-stack-protector)

diff --git a/drivers/xen/fallback.c b/drivers/xen/fallback.c
new file mode 100644 (file)
index 0000000..0ef7c4d
--- /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;
+}