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authorMichael S. Tsirkin <mst@redhat.com>2020-04-06 15:12:47 +0300
committerMichael S. Tsirkin <mst@redhat.com>2020-04-20 17:19:22 +0300
commitd085eb8ce727e581abf8145244eaa3339021be2f (patch)
treece3b3b41cb4c7a5eec3c0320a315210bfe5d007f /drivers/vhost
parent15064e70909cd8cca092ed6dd888bdbd9fefaae3 (diff)
downloadlinux-d085eb8ce727e581abf8145244eaa3339021be2f.tar.xz
vhost: disable for OABI
vhost is currently broken on the some ARM configs. The reason is that the ring element addresses are passed between components with different alignments assumptions. Thus, if guest selects a pointer and host then gets and dereferences it, then alignment assumed by the host's compiler might be greater than the actual alignment of the pointer. compiler on the host from assuming pointer is aligned. This actually triggers on ARM with -mabi=apcs-gnu - which is a deprecated configuration. With this OABI, compiler assumes that all structures are 4 byte aligned - which is stronger than virtio guarantees for available and used rings, which are merely 2 bytes. Thus a guest without -mabi=apcs-gnu running on top of host with -mabi=apcs-gnu will be broken. The correct fix is to force alignment of structures - however that is an intrusive fix that's best deferred until the next release. We didn't previously support such ancient systems at all - this surfaced after vdpa support prompted removing dependency of vhost on VIRTULIZATION. So for now, let's just add something along the lines of depends on !ARM || AEABI to the virtio Kconfig declaration, and add a comment that it has to do with struct member alignment. Note: we can't make VHOST and VHOST_RING themselves have a dependency since these are selected. Add a new symbol for that. We should be able to drop this dependency down the road. Fixes: 20c384f1ea1a0bc7 ("vhost: refine vhost and vringh kconfig") Suggested-by: Ard Biesheuvel <ardb@kernel.org> Suggested-by: Richard Earnshaw <Richard.Earnshaw@arm.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Diffstat (limited to 'drivers/vhost')
-rw-r--r--drivers/vhost/Kconfig17
1 files changed, 13 insertions, 4 deletions
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 2c75d164b827..c4f273793595 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -13,6 +13,15 @@ config VHOST_RING
This option is selected by any driver which needs to access
the host side of a virtio ring.
+config VHOST_DPN
+ bool
+ depends on !ARM || AEABI
+ default y
+ help
+ Anything selecting VHOST or VHOST_RING must depend on VHOST_DPN.
+ This excludes the deprecated ARM ABI since that forces a 4 byte
+ alignment on all structs - incompatible with virtio spec requirements.
+
config VHOST
tristate
select VHOST_IOTLB
@@ -28,7 +37,7 @@ if VHOST_MENU
config VHOST_NET
tristate "Host kernel accelerator for virtio net"
- depends on NET && EVENTFD && (TUN || !TUN) && (TAP || !TAP)
+ depends on NET && EVENTFD && (TUN || !TUN) && (TAP || !TAP) && VHOST_DPN
select VHOST
---help---
This kernel module can be loaded in host kernel to accelerate
@@ -40,7 +49,7 @@ config VHOST_NET
config VHOST_SCSI
tristate "VHOST_SCSI TCM fabric driver"
- depends on TARGET_CORE && EVENTFD
+ depends on TARGET_CORE && EVENTFD && VHOST_DPN
select VHOST
default n
---help---
@@ -49,7 +58,7 @@ config VHOST_SCSI
config VHOST_VSOCK
tristate "vhost virtio-vsock driver"
- depends on VSOCKETS && EVENTFD
+ depends on VSOCKETS && EVENTFD && VHOST_DPN
select VHOST
select VIRTIO_VSOCKETS_COMMON
default n
@@ -63,7 +72,7 @@ config VHOST_VSOCK
config VHOST_VDPA
tristate "Vhost driver for vDPA-based backend"
- depends on EVENTFD
+ depends on EVENTFD && VHOST_DPN
select VHOST
depends on VDPA
help