[Xen-devel] [PATCH] [v3] xen: remove pre-xen3 fallback handlers

[Arnd Bergmann <arnd@xxxxxxxx>]

The legacy hypercall handlers were originally added with
a comment explaining that "copying the argument structures in
HYPERVISOR_event_channel_op() and HYPERVISOR_physdev_op() into the local
variable is sufficiently safe" and only made sure to not write
past the end of the argument structure, the checks in linux/string.h
disagree with that, when link-time optimizations are used:

In function 'memcpy',
    inlined from 'pirq_query_unmask' at drivers/xen/fallback.c:53:2,
    inlined from '__startup_pirq' at drivers/xen/events/events_base.c:529:2,
    inlined from 'restore_pirqs' at drivers/xen/events/events_base.c:1439:3,
    inlined from 'xen_irq_resume' at drivers/xen/events/events_base.c:1581:2:
include/linux/string.h:350:3: error: call to '__read_overflow2' declared with 
attribute error: detected read beyond size of object passed as 2nd parameter
   __read_overflow2();
   ^

Further research turned out that only Xen 3.0.2 or earlier required the
fallback at all, while all versions in use today don't need it.
As far as I can tell, it is not even possible to run a mainline kernel
on those old Xen releases, at the time when they were in use, only
a patched kernel was supported anyway.

Fixes: cf47a83fb06e ("xen/hypercall: fix hypercall fallback code for very old 
hypervisors")
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
[v2] use a table lookup instead of a switch/case statement, after
multiple suggestions.
[v3] remove that file completely
---
 arch/x86/include/asm/xen/hypercall.h | 13 +-----
 drivers/xen/Makefile                 |  1 -
 drivers/xen/fallback.c               | 81 ------------------------------------
 3 files changed, 2 insertions(+), 93 deletions(-)
 delete mode 100644 drivers/xen/fallback.c

diff --git a/arch/x86/include/asm/xen/hypercall.h 
b/arch/x86/include/asm/xen/hypercall.h
index bfd882617613..dcf9353a662a 100644
--- a/arch/x86/include/asm/xen/hypercall.h
+++ b/arch/x86/include/asm/xen/hypercall.h
@@ -365,15 +365,11 @@ 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))
-               rc = xen_event_channel_op_compat(cmd, arg);
-       return rc;
+       return _hypercall2(int, event_channel_op, cmd, arg);
 }
 
 static inline int
@@ -388,15 +384,10 @@ HYPERVISOR_console_io(int cmd, int count, char *str)
        return _hypercall3(int, console_io, cmd, count, str);
 }
 
-extern int __must_check xen_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))
-               rc = xen_physdev_op_compat(cmd, arg);
-       return rc;
+       return _hypercall2(int, physdev_op, cmd, arg);
 }
 
 static inline int
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 451e833f5931..ea2485069e19 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -1,6 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_HOTPLUG_CPU)              += cpu_hotplug.o
-obj-$(CONFIG_X86)                      += fallback.o
 obj-y  += grant-table.o features.o balloon.o manage.o preempt.o time.o
 obj-y  += events/
 obj-y  += xenbus/
diff --git a/drivers/xen/fallback.c b/drivers/xen/fallback.c
deleted file mode 100644
index b04fb64c5a91..000000000000
--- a/drivers/xen/fallback.c
+++ /dev/null
@@ -1,81 +0,0 @@
-#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 xen_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;
-}
-EXPORT_SYMBOL_GPL(xen_physdev_op_compat);
-- 
2.9.0


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