[PATCH u-boot v2019.04-aspeed-openbmc v3] aspeed: Disable backdoor interfaces

[Andrew Jeffery]

On Wed, 20 Apr 2022, at 12:36, Ryan Chen wrote:
>> -----Original Message-----
>> From: Zev Weiss <zev at bewilderbeest.net>
>> Sent: Wednesday, April 20, 2022 7:42 AM
>> To: Joel Stanley <joel at jms.id.au>; openbmc at lists.ozlabs.org
>> Cc: Zev Weiss <zev at bewilderbeest.net>; Andrew Jeffery <andrew at aj.id.au>;
>> Ryan Chen <ryan_chen at aspeedtech.com>; Ian Woloschin
>> <ian.woloschin at akamai.com>; Lei Yu <yulei.sh at bytedance.com>
>> Subject: [PATCH u-boot v2019.04-aspeed-openbmc v3] aspeed: Disable
>> backdoor interfaces
>> 
>> On ast2400 and ast2500 we now disable the various hardware backdoor
>> interfaces as is done on ast2600.  Two Kconfig options can selectively
>> re-enable some of these interfaces: CONFIG_ASPEED_ENABLE_SUPERIO leaves
>> the ast2x00 built-in Super I/O device enabled, as it is required for some
>> systems, and CONFIG_ASPEED_ENABLE_DEBUG_UART leaves the hardware
>> debug UART enabled, since it provides a relatively high ratio of utility to
>> security risk during development.
>> 
>> This patch is based on a patch by Andrew Jeffery for an older u-boot branch in
>> the OpenBMC tree for the df-isolate-bmc distro feature flag.
>> 
>> Signed-off-by: Zev Weiss <zev at bewilderbeest.net>
>> ---
>> 
>> Tested on ast2500 and (hostless, BMC-only) ast2400.
>> 
>> Ryan, are you OK with having an option (off by default) to leave the debug
>> UART enabled as in this version of the patch?
>> 
> Thanks your submit.
> Again, my opinion still keep the direct patch to disable it.
> Not have config to enable it.
>

Ideally yes, but as Ian mentioned he has at least one system where the 
SuperIO AHB bridge must be enabled to allow their BIOS to configure the 
UARTs. So we need an option to cater to that.

I don't want people to have to patch the code to allow use of the 
backdoors, that will just lead to other problems (e.g. reverting this 
patch is the simplest thing, and opens up all the backdoors instead of 
a targeted one).

Andrew