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Date: Fri, 2 Nov 2012 12:44:09 -0400
From: Konrad Rzeszutek Wilk <konrad@...nel.org>
To: Jan Beulich <JBeulich@...e.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
xen-devel <xen-devel@...ts.xen.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] xen/hypercall: fix hypercall fallback code for very
old hypervisors
On Wed, Oct 31, 2012 at 08:55:54AM +0000, Jan Beulich wrote:
> >>> On 30.10.12 at 16:44, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
> > On Mon, Oct 29, 2012 at 10:08:17AM -0400, Konrad Rzeszutek Wilk wrote:
> >> From: Jan Beulich <jbeulich@...e.com>
> >>
> >> 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@...cle.com>
> >> Signed-off-by: Jan Beulich <jbeulich@...e.com>
> >> [v2: Reduce #define/#undef usage in HYPERVISOR_physdev_op_compat().]
> >> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> >
> > And it looks like I get
> >
> > ERROR: "HYPERVISOR_event_channel_op_compat" [drivers/xen/xen-evtchn.ko]
> > undefined!
> >
> > when I build xen-evtchn as module. Jan did you encounter this issue on
> > 2.6.18?
>
> No - the event channel driver there can't be built as a module, and
> for the forward ported kernels I apparently never tried to build with
> a compat setting of 3.0.2 or less (and I didn't care that much either
> because the oldest we're actually concerned about is 3.0.4 to cover
> some of those very old EC2 systems; I'll add the export at the right
> point nevertheless).
Ok, ended up with this version which I was thinking to for v3.7-rc5:
>From 4ae4c7658a7c0501521c422d618038587c3edeca Mon Sep 17 00:00:00 2001
From: Jan Beulich <jbeulich@...e.com>
Date: Fri, 19 Oct 2012 15:25:37 -0400
Subject: [PATCH] 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@...cle.com>
Signed-off-by: Jan Beulich <jbeulich@...e.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_..]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
---
arch/x86/include/asm/xen/hypercall.h | 21 ++++------
drivers/xen/Makefile | 2 +-
drivers/xen/fallback.c | 81 ++++++++++++++++++++++++++++++++++++
3 files changed, 89 insertions(+), 15 deletions(-)
create 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 59c226d..4055421 100644
--- 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_HYPERVISOR_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_HYPERVISOR_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 xen_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 = xen_HYPERVISOR_physdev_op_compat(cmd, arg);
return rc;
}
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 0e863703..46de6cd 100644
--- 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
index 0000000..b29ce32
--- /dev/null
+++ b/drivers/xen/fallback.c
@@ -0,0 +1,81 @@
+#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_HYPERVISOR_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_HYPERVISOR_event_channel_op_compat);
+
+int xen_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;
+}
+EXPORT_SYMBOL_GPL(xen_HYPERVISOR_physdev_op_compat);
--
1.7.11.7
--
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