[U-Boot] Unexpected saving of all environment variables during EFI boot

Rob Clark
2017-10-19T21:15:50Z

On Thu, Oct 19, 2017 at 5:05 PM, Alexander Graf <agraf@suse.de> wrote:
>
>
> On 19.10.17 22:40, Heinrich Schuchardt wrote:
>> This was merged as
>> ad644e7c18238026fecc647f62584d87d2c5b0a3
>> efi_loader: efi variable support
>>
>>> diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
>>> index ec40f41bcb..c406ff82ff 100644
>>> --- a/lib/efi_loader/efi_boottime.c
>>> +++ b/lib/efi_loader/efi_boottime.c
>>> @@ -8,6 +8,7 @@
>>>
>>> #include <common.h>
>>> #include <efi_loader.h>
>>> +#include <environment.h>
>>> #include <malloc.h>
>>> #include <asm/global_data.h>
>>> #include <libfdt_env.h>
>>> @@ -942,6 +943,11 @@ static efi_status_t EFIAPI efi_exit_boot_services(void *image_handle,
>>> {
>>> EFI_ENTRY("%p, %ld", image_handle, map_key);
>>>
>>> +#if defined(CONFIG_CMD_SAVEENV) && !defined(CONFIG_ENV_IS_NOWHERE)
>>> + /* save any EFI variables that have been written: */
>>> + env_save();
>>
>> You save all changed variables and not specifically those bound to EFI.
>> This is completely unexpected behavior for the user and not covered by
>> the commit message.
>>
>> Furthermore you call env_save even if no EFI variable has been touched
>> at all.
>>
>> This leads to writing to flash on every boot via EFI. Depending on
>> technology this might ruin the flash after a few hundred reboots.
>
> I agree that overwriting flash on every boot isn't a terribly smart idea.
>
> Also saving random environment variables that are set while we are in a
> distro loop to persistent storage isn't great either.
>
> I agree that we should probably improve this code to only save efi
> variables.
>
> Rob, how bad would it be for Fedora if we remove the persistent variable
> store call (just the env_save() line) for 2017.11 to not kill people's
> storage devices? Then for the next version tackle it for real and only
> save efi variable changes here and only if anything really did change.
>

As I mentioned on #u-boot, I think we can just comment the
env_save().. or perhaps make it a config option. It will be mildly
annoying, since it means every boot is "first boot", ie. falling back
to fallback.efi to populate BootOrder/BootNNNN variables, and never
using bootmgr. But since we can't set EFI variables from userspace
yet, it isn't really a regression (yet).

Longer term, maybe we need to split out EFI variables from u-boot env
vars.. I thought it would be nice to store them together, since it
gives a convenient way to set EFI variables from script or cmdline.
But at least a subset of the EFI vars should be persisted to reach
EBBR, and if that breaks expectations about u-boot env vars, then I
guess we need to split them.

Side note, devices that can't repeatedly save env (even if we split
out the EFI variables to be stored separately) might be problematic
with EFI_LOADER. Maybe we need a build option they can set to have a
more crippled version of EFI_LOADER, so as to not penalize more
capable devices.

BR,
-R