Question: how to identify vendor firmware setups conflicting with disk partitions?
steve.mcintyre at linaro.org
Thu Feb 28 17:12:25 UTC 2019
I've just been having a discussion with folks about installing Debian
on an arm64 device. Another developer is booting via U-Boot with UEFI
and things are working OK, except...
The intructions for their board  include writing things raw to both
sector 0 and sector 1 of an SD card, meaning that both MBR and GPT
partitioning schemes are likely to break. Ugh. :-/
So, I have two (related) worries:
1. At the moment in Debian, our installer will default to using GPT
for arm64 machines (where disks are not already formatted). That
was fine when we were expecting server systems booting using edk2,
but it looks like that's now a dangerous assumption, as more and
more U-Boot devices are out there which will be wanting to load
firmware from low-numbered LBAs.
2. I'm just in the middle of adding EFI armhf installer support, and
that is also (currently) defaulting to GPT if you've booted via
EFI. This is fine for VMs booted using a 32-bit Arm build of edk2,
but also it's starting to look like a bad option for real boards
booting using U-Boot's EFI support (for similar reasons).
The "Firmware Storage" section of EBBR v0.6 touches on this and
describes how to store firmware in a safer manner, but obviously
(some/many) vendors are not following the spec thus far. What are
other folks doing in this area? How do you recognise which devices
it's safe to use GPT on, for example?
I'm now looking at updating our logic on armhf/arm64 to do something
if (booted via UEFI); then
if (booted using U-Boot); then
but I'll need to find a sane way to detect U-Boot->UEFI boot. For now
I'm looking at parsing dmesg output to look for something like
[ 0.000000] efi: EFI v2.70 by Das U-Boot
but I'm hoping for a better solution. This is also somewhat assuming
that detecting U-Boot in the boot chain is a valid indicator for
"unsafe location for firmware", but I'm not sure of a better way!
Steve McIntyre steve.mcintyre at linaro.org
<http://www.linaro.org/> Linaro.org | Open source software for ARM SoCs
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