linux-kernel - Re: BUG and WARN kernel log levels

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Date:	Mon, 15 Aug 2016 13:39:40 -0700
From:	Joe Perches <joe@...ches.com>
To:	Kees Cook <keescook@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: BUG and WARN kernel log levels

On Mon, 2016-08-15 at 13:28 -0700, Kees Cook wrote:
> On Mon, Aug 15, 2016 at 12:00 PM, Joe Perches <joe@...ches.com> wrote:
> > On Mon, 2016-08-15 at 11:53 -0700, Kees Cook wrote:
> > > So, I noticed that asm-gemeric/bug.h defines BUG() without a log level:
> > > 
> > > #ifndef HAVE_ARCH_BUG
> > > #define BUG() do { \
> > >        printk("BUG: failure at %s:%d/%s()!\n", __FILE__, __LINE__, __func__); \
> > > 
> > > Seems like it should have one?
> > > 
> > > Also, I think we might want to examine WARN() a bit... it doesn't have
> > > a log level either, but only a fraction of callers set one:
> > > 
> > > $ git grep -E 'WARN(_TAINT|)(_RATELIMIT|_ONCE|)\([^\)]' | grep -v KERN_ | wc -l
> > > 2735
> > > 
> > > $ git grep -E 'WARN(_TAINT|)(_RATELIMIT|_ONCE|)\([^\)]' | grep KERN_ | wc -l
> > > 77
> > > 
> > > If I'm reading checkpatch.pl correctly, it doesn't warn about missing
> > > log levels on WARN calls, but I think it should.
> > > 
> > > How do you think is best to clean this up?
> > > 
> > > Mainly, I'd like to add a format string to BUG, or introduce a new
> > > BUGish call that takes a format...
> > I once suggested something similar awhile ago.
> > https://lkml.org/lkml/2008/7/8/261
> > 
> > I think it's best to remove any KERN_ from the use of
> > all the WARN variants and add it to the WARN definitions.
> Yeah, that's what I was thinking too. It does mean that the format
> needs to be a const char string, though.

No it doesn't mean that.

Prefixing KERN_WARNING to the const char[] types and using
KERN_WARNING "%pV" could work for the non const char[] types

Or maybe use the same KERN_WARNING "%pV" for simpler code.

> > Same with BUG.
> Yeah, though for full effect, it needs to be plumbed into each
> architecture's BUG handler. Mainly what I don't like is that if I do
> this on x86:
> 
> pr_err("eek, terrible thing\n");
> BUG();
> 
> I get a dmesg that read:
> 
> eek, terrible thing
> === cut here ===
> ...traceback, etc
> 
> I'd like the "eek" part to be inside the "cut here". And I'd like BUGs
> to be able to be more verbose.

Maybe add BUG_MSG/BUG_ON_MSG or some such.