[v11,2/2] s390: virtio: PV needs VIRTIO I/O device protection

Commit Message

Pierre Morel Sept. 7, 2020, 9:39 a.m. UTC

If protected virtualization is active on s390, VIRTIO has only retricted
access to the guest memory.
Define CONFIG_ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS and export
arch_has_restricted_virtio_memory_access to advertize VIRTIO if that's
the case, preventing a host error on access attempt.

Signed-off-by: Pierre Morel <[e-mail]>
Reviewed-by: Cornelia Huck <[e-mail]>
---
 arch/s390/Kconfig   |  1 +
 arch/s390/mm/init.c | 10 ++++++++++
 2 files changed, 11 insertions(+)

Comments

Halil Pasic Sept. 7, 2020, 10:37 p.m. UTC | #1

On Mon,  7 Sep 2020 11:39:07 +0200
Pierre Morel <[e-mail]> wrote:

> If protected virtualization is active on s390, VIRTIO has only retricted
> access to the guest memory.
> Define CONFIG_ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS and export
> arch_has_restricted_virtio_memory_access to advertize VIRTIO if that's
> the case, preventing a host error on access attempt.

The description is a little inaccurate, but I don't care hence the r-b.

The function arch_has_restricted_virtio_memory_access() returning true
can not prevent the host from attempting to access memory if it decides
to do so. And as far as I know there was no host error on access attempt.
The page gets exported, and the host will operate on the encrypted
page. But in the end we do run into trouble, which is usually fatal for
the guest (not the host).

What we actually do here is the following. If we detect
an ill configured device we fail it (device status field), because
attempting to drive it is a recipe for disaster.

> 
> Signed-off-by: Pierre Morel <[e-mail]>
> Reviewed-by: Cornelia Huck <[e-mail]>

Reviewed-by: Halil Pasic <[e-mail]>

Patch

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index b29fcc66ec39..938246200d39 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -820,6 +820,7 @@  menu "Virtualization"
 config PROTECTED_VIRTUALIZATION_GUEST
 	def_bool n
 	prompt "Protected virtualization guest support"
+	select ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS
 	help
 	  Select this option, if you want to be able to run this
 	  kernel as a protected virtualization KVM guest.
diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 0d282081dc1f..f40b9b63d3d6 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -160,6 +160,16 @@  bool force_dma_unencrypted(struct device *dev)
 	return is_prot_virt_guest();
 }
 
+#ifdef CONFIG_ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS
+
+int arch_has_restricted_virtio_memory_access(void)
+{
+	return is_prot_virt_guest();
+}
+EXPORT_SYMBOL(arch_has_restricted_virtio_memory_access);
+
+#endif
+
 /* protected virtualization */
 static void pv_init(void)
 {