[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH v7 12/12] xen: clarify the security-support status of Kconfig options on ARM

On 24/07/18 23:31, Stefano Stabellini wrote:
On Mon, 23 Jul 2018, Julien Grall wrote:

On 07/07/18 00:14, Stefano Stabellini wrote:
Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: George.Dunlap@xxxxxxxxxxxxx
CC: Ian.Jackson@xxxxxxxxxxxxx
CC: jbeulich@xxxxxxxx
CC: andrew.cooper3@xxxxxxxxxx
   SUPPORT.md | 10 ++++++++++
   1 file changed, 10 insertions(+)

diff --git a/SUPPORT.md b/SUPPORT.md
index e3e49e2..151a63d 100644
--- a/SUPPORT.md
+++ b/SUPPORT.md
@@ -22,6 +22,16 @@ EXPERT and DEBUG Kconfig options are not security
supported. Other
   Kconfig options are supported, if the related features are marked as
   supported in this document.
   +On ARM, a wider range of Kconfig configurations is available to enable
+very small lines of code counts in the hypervisor. Not all possible
+combinations of kconfig options are security supported. Instead, a few

NIT: s/kconfig/Kconfig/

+pre-canned configurations have been added to xen/arch/arm/configs: they
+are security suppored. Configurations derived from the pre-canned files


I'll fix

+by adding non-listed options with their default values, or by enabling
+any of the platform options under "Platform Support" (and their
+dependent options) are security supported, unless stated

I am not entirely sure to understand the implications the paragraph.

It is meant to say:

1) xen/arch/arm/configs config files are security supported
2) default values of any kconfig options are security supported
3) if an option is marked as not security supported in SUPPORT.md, then
    it is not security supported, no matter the default value
4) everything else is not security supported
Should I try to clarify it? I guess I should make clear that a .config
with an unsupported option is unsupported as a whole. I can add:

  "A configuration with one or more unsupported options, is not

For instance, if I choose arm64_defconfig, memaccess will be enabled by
default but any use of it is not security supported. What will be the state of
the security support for that .config?

Yes, memaccess will default to enable. However, SUPPORT.md says it is
not security supported, hence, the result is that the .config is not
security supported, according to (3).

We really don't want that. That arm64_defconfig is the default config for Xen. Anyone using it will not be security supported.

Distros will likely use the default config as it enables everything. If I were a package maintainer, I would expect at minimum to security support the .config. This does not mean that using a specific feature will be supported.

There is a catch though. In the specific case of memaccess, SUPPORT.md
only states the following:

### Virtual Machine Introspection

     Status, x86: Supported, not security supported

Which doesn't say anything about ARM. It would be a good idea to do the
same that x86 is doing (Supported, not security supported)?

Memaccess has never been considered to be supported on Arm, yet it is enabled by default as on x86. However, most of the code in that context is gated by "memaccess_enabled". So what is not security supported is the use of memaccess.


Julien Grall

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.