[PATCH v1] Bug-fixes for v3.7 back-ported from Jan's postings.

[PATCH v1] Bug-fixes for v3.7 back-ported from Jan's postings.

[Konrad Rzeszutek Wilk]

These are back-ports from the ones that Jan posted. Please
take a look  - I might have missed an email about one of the patches
and I can't find it my mailbox :-(

Either way, was thinking to put these in v3.7.

 arch/x86/include/asm/xen/hypercall.h     |   21 +++-----
 drivers/xen/Makefile                     |    2 +-
 drivers/xen/fallback.c                   |   78 ++++++++++++++++++++++++++++++
 drivers/xen/xenbus/xenbus_dev_frontend.c |    2 +-
 4 files changed, 87 insertions(+), 16 deletions(-)


Jan Beulich (2):
      xen/hypercall: fix hypercall fallback code for very old hypervisors
      xen/xenbus: fix overflow check in xenbus_file_write()

[PATCH 1/2] xen/hypercall: fix hypercall fallback code for very old hypervisors

[Konrad Rzeszutek Wilk]

From: Jan Beulich <jbeulich@suse.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@oracle.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
[v2: Reduce #define/#undef usage in HYPERVISOR_physdev_op_compat().]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 arch/x86/include/asm/xen/hypercall.h |   21 +++------
 drivers/xen/Makefile                 |    2 +-
 drivers/xen/fallback.c               |   78 ++++++++++++++++++++++++++++++++++
 3 files changed, 86 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..c812360 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);
 }
+int __must_check 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 = 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);
 }
 
+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 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..0bdc468
--- /dev/null
+++ b/drivers/xen/fallback.c
@@ -0,0 +1,78 @@
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/bug.h>
+#include <asm/hypervisor.h>
+#include <asm/xen/hypercall.h>
+
+int 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;
+}
+
+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;
+}
-- 
1.7.7.6

Re: [PATCH 1/2] xen/hypercall: fix hypercall fallback code for very old hypervisors

[Konrad Rzeszutek Wilk]

On Mon, Oct 29, 2012 at 10:08:17AM -0400, Konrad Rzeszutek Wilk wrote:
> From: Jan Beulich <jbeulich@suse.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@oracle.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> [v2: Reduce #define/#undef usage in HYPERVISOR_physdev_op_compat().]
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.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?
> ---
>  arch/x86/include/asm/xen/hypercall.h |   21 +++------
>  drivers/xen/Makefile                 |    2 +-
>  drivers/xen/fallback.c               |   78 ++++++++++++++++++++++++++++++++++
>  3 files changed, 86 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..c812360 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);
>  }
> +int __must_check 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 = 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);
>  }
>  
> +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 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..0bdc468
> --- /dev/null
> +++ b/drivers/xen/fallback.c
> @@ -0,0 +1,78 @@
> +#include <linux/kernel.h>
> +#include <linux/string.h>
> +#include <linux/bug.h>
> +#include <asm/hypervisor.h>
> +#include <asm/xen/hypercall.h>
> +
> +int 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;
> +}
> +
> +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;
> +}
> -- 
> 1.7.7.6

Re: [PATCH 1/2] xen/hypercall: fix hypercall fallback code for very old hypervisors

[Jan Beulich]

>>> On 30.10.12 at 16:44, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> On Mon, Oct 29, 2012 at 10:08:17AM -0400, Konrad Rzeszutek Wilk wrote:
>> From: Jan Beulich <jbeulich@suse.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@oracle.com>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> [v2: Reduce #define/#undef usage in HYPERVISOR_physdev_op_compat().]
>> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.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).

Jan

>> ---
>>  arch/x86/include/asm/xen/hypercall.h |   21 +++------
>>  drivers/xen/Makefile                 |    2 +-
>>  drivers/xen/fallback.c               |   78 
> ++++++++++++++++++++++++++++++++++
>>  3 files changed, 86 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..c812360 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);
>>  }
>> +int __must_check 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 = 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);
>>  }
>>  
>> +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 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..0bdc468
>> --- /dev/null
>> +++ b/drivers/xen/fallback.c
>> @@ -0,0 +1,78 @@
>> +#include <linux/kernel.h>
>> +#include <linux/string.h>
>> +#include <linux/bug.h>
>> +#include <asm/hypervisor.h>
>> +#include <asm/xen/hypercall.h>
>> +
>> +int 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;
>> +}
>> +
>> +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;
>> +}
>> -- 
>> 1.7.7.6

Re: [PATCH 1/2] xen/hypercall: fix hypercall fallback code for very old hypervisors

[Konrad Rzeszutek Wilk]

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@oracle.com> wrote:
> > On Mon, Oct 29, 2012 at 10:08:17AM -0400, Konrad Rzeszutek Wilk wrote:
> >> From: Jan Beulich <jbeulich@suse.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@oracle.com>
> >> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> >> [v2: Reduce #define/#undef usage in HYPERVISOR_physdev_op_compat().]
> >> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.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@suse.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@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_..]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.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

Re: [PATCH 1/2] xen/hypercall: fix hypercall fallback code for very old hypervisors

[Jan Beulich]

>>> On 02.11.12 at 17:44, Konrad Rzeszutek Wilk <konrad@kernel.org> wrote:
> --- 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 *);

Why don't you drop the HYPERVISOR_ now that you added the xen_?

>...
> +EXPORT_SYMBOL_GPL(xen_HYPERVISOR_event_channel_op_compat);

While this export is necessary, ...

>...
> +EXPORT_SYMBOL_GPL(xen_HYPERVISOR_physdev_op_compat);

... I would recommend not adding this one without need.

Jan

[PATCH 2/2] xen/xenbus: fix overflow check in xenbus_file_write()

[Konrad Rzeszutek Wilk]

From: Jan Beulich <JBeulich@suse.com>

Acked-by: Ian Campbell <ian.campbell@citrix.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
[v1: Rebased on upstream]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 drivers/xen/xenbus/xenbus_dev_frontend.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c b/drivers/xen/xenbus/xenbus_dev_frontend.c
index 89f7625..ac72702 100644
--- a/drivers/xen/xenbus/xenbus_dev_frontend.c
+++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
@@ -458,7 +458,7 @@ static ssize_t xenbus_file_write(struct file *filp,
 		goto out;
 
 	/* Can't write a xenbus message larger we can buffer */
-	if ((len + u->len) > sizeof(u->u.buffer)) {
+	if (len > sizeof(u->u.buffer) - u->len) {
 		/* On error, dump existing buffer */
 		u->len = 0;
 		rc = -EINVAL;
-- 
1.7.7.6