On Fri, Feb 16, 2018 at 09:09:30PM +0000, Luck, Tony wrote:
> > That said, I'm not sure how many non-root users run the toolkit to
> > extract their EFI certificates or check on the secure boot status of
> > the system, but I suspect it might be non-zero: I can see the tinfoil
> > hat people wanting at least to check the secure boot status when they
> > log in.
>
> Another fix option might be to rate limit EFI calls for non-root users (on X86
> since only we have the SMI problem). That would:
>
> 1) Avoid using memory to cache all the variables
> 2) Catch any other places where non-root users can call EFI
I could get behind that as well. Currently the things I maintain do
approximately this many normal accesses with invocations you can do as a
user:
"efibootmgr -v" - six files we always try to read, plus one per Boot####
entry.
"fwupdate --info" - one file it always tries to read, one file for each
ESRT entry.
"dbxtool -l" - one file it always reads.
"mokutil --sb-state" - reads the same file twice. I don't maintain
this, but I'll send a patch to Gary to make it
only read it once. AFAICS all of the other
invocations you can currently do as a user
/legitimately/ read two files, though.
Some systems seem to *love* making a pile of Boot#### entries; I think
the most I've seen is something like 16. So on that machine, one
"efibootmgr -v" invocation is ~22 efivars files read. I've never seen a
machine that advertised more than 2 ESRT entries, but maybe we'll get
there some day.
--
Peter
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