Re: [PATCH 1/2] fs/efivarfs: restrict inode permissions

[Luck, Tony]

On Tue, Feb 20, 2018 at 02:01:51PM -0800, Linus Torvalds wrote:
> And just on general principlies, I don't want to see weasel-wordy
> commit messages like
> 
>  "Reading certain EFI variables trigger SMIs"
> 
> I understand *writing* them causing SMI's due to some flash protection
> scheme. What's the reading thing? And why aren't we calling that
> garbage out?

Too much weasel there.  Should say:

EFI[1] stinks. Reading any file in /sys/firmware/efi/efivars/ generates
4 (yes FOUR!) SMIs.

# rdmsr 0x34
14e2
# cat /sys/firmware/efi/efivars/ConIn-8be4df61-93ca-11d2-aa0d-00e098032b8c > /dev/null
# rdmsr 0x34
14e6

-Tony

[1] I didn't dig through the Linux code to check whether we manage to
get those four SMIs from a single EFI call, or whether we make multiple
EFI calls to open/read/close one file. It is possible that we stink a
bit too if we are doing more EFI calls than required.