On 24/07/18 23:31, Stefano Stabellini wrote:
On Mon, 23 Jul 2018, Julien Grall wrote:
Hi,
On 07/07/18 00:14, Stefano Stabellini wrote:
Signed-off-by: Stefano Stabellini <sstabell...@kernel.org>
CC: george.dun...@eu.citrix.com
CC: ian.jack...@eu.citrix.com
CC: jbeul...@suse.com
CC: andrew.coop...@citrix.com
---
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
s/suppored/supported/
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
+otherwise.
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
unsupported."
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.
Cheers,
--
Julien Grall
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