Messages in this thread | | | Date | Mon, 8 Apr 2019 21:08:00 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86/mm/mem_encrypt: Disable all instrumentation for SME early boot code |
| |
On Mon, Apr 08, 2019 at 06:41:30PM +0000, Gary R Hook wrote: > Again, not arguing. I completely understand. However, to be fair, this > isn't about SME having trouble with those facilities, this is about > using certain features (e.g. command line option processing) early in > the boot. Any complex feature could have had that requirement, don't you > think?
Sure, but then why do we need that patch at all then? Why do we need to disable instrumentation for SME early code and not for other early code?
I mean, if you grep around the tree you can see a bunch of KASAN_SANITIZE but in lib/ we only have
lib/Makefile:210:KASAN_SANITIZE_stackdepot.o := n
which is special. But the rest of the generic code in lib/ or arch/x86/lib/ isn't.
Now, there's this:
arch/x86/boot/Makefile:12:KASAN_SANITIZE := n arch/x86/boot/compressed/Makefile:20:KASAN_SANITIZE := n
which disables KASAN for all boot code.
And this is what you mean - all early boot code should not be sanitized.
Which also gives the right solution, IMO:
cmdline.o should not be sanitized only when used in the boot code. But that is already the case.
So why do you need to disable KASAN for arch/x86/lib/cmdline.c?
Because for those two:
arch/x86/boot/cmdline.c arch/x86/boot/compressed/cmdline.c
that should already be the case due to the Makefile defines above.
> Right. My goal was to get a conversation started, because folks are > running into this problem when KASAN is enabled.
You say KASAN. Why is there KCOV_INSTRUMENT_cmdline.o too?
> N.B. Here's another facet of this problem: cmdline.c doesn't (today) > contain anything that would trigger the stack protector. However, it's > possible to enable the stack protector globally when building, right? In > which case, a boot would fail, so we have the same issue: early boot > code has special requirements / restrictions.
How so?
This .config boots here in a vm just fine.
$ grep STACKPROT .config CONFIG_CC_HAS_SANE_STACKPROTECTOR=y CONFIG_HAVE_STACKPROTECTOR=y CONFIG_CC_HAS_STACKPROTECTOR_NONE=y CONFIG_STACKPROTECTOR=y CONFIG_STACKPROTECTOR_STRONG=y
-- Regards/Gruss, Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
| |