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 <[email protected]>
---
[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
On 03/13/2018 05:06 PM, Arnd Bergmann wrote:
> 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 <[email protected]>
> ---
> [v2] use a table lookup instead of a switch/case statement, after
> multiple suggestions.
> [v3] remove that file completely
(+Jan who added this file originally)
Reviewed-by: Boris Ostrovsky <[email protected]>
>>> On 14.03.18 at 23:47, <[email protected]> wrote:
> On 03/13/2018 05:06 PM, Arnd Bergmann wrote:
>> 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 <[email protected]>
>> ---
>> [v2] use a table lookup instead of a switch/case statement, after
>> multiple suggestions.
>> [v3] remove that file completely
>
> (+Jan who added this file originally)
Well, if everyone thinks backwards compatibility to those very old
hypervisors is not relevant anymore, then I'm not going to object.
It's really a matter of the consuming distros to know how far back
they want/need to guarantee compatibility.
Jan