linux-kernel - Re: [PATCH 2/4] x86/dumpstack: remove kernel text addresses from stack dump

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Date:   Mon, 28 Nov 2016 14:49:58 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <alexander.levin@...izon.com>,
        Konstantin Khlebnikov <koct9i@...il.com>
Subject: Re: [PATCH 2/4] x86/dumpstack: remove kernel text addresses from
 stack dump

On Fri, Nov 25, 2016 at 03:26:04PM +0300, Kirill A. Shutemov wrote:
> On Tue, Oct 25, 2016 at 09:51:12AM -0500, Josh Poimboeuf wrote:
> > Printing kernel text addresses in stack dumps is of questionable value,
> > especially now that address randomization is becoming common.
> > 
> > It can be a security issue because it leaks kernel addresses.  It also
> > affects the usefulness of the stack dump.  Linus says:
> > 
> >   "I actually spend time cleaning up commit messages in logs, because
> >   useless data that isn't actually information (random hex numbers) is
> >   actively detrimental.
> > 
> >   It makes commit logs less legible.
> > 
> >   It also makes it harder to parse dumps.
> > 
> >   It's not useful. That makes it actively bad.
> > 
> >   I probably look at more oops reports than most people. I have not
> >   found the hex numbers useful for the last five years, because they are
> >   just randomized crap.
> > 
> >   The stack content thing just makes code scroll off the screen etc, for
> >   example."
> > 
> > The only real downside to removing these addresses is that they can be
> > used to disambiguate duplicate symbol names.  However such cases are
> > rare, and the context of the stack dump should be enough to be able to
> > figure it out.
> > 
> > There's now a 'faddr2line' script which can be used to convert a
> > function address to a file name and line:
> > 
> >   $ ./scripts/faddr2line ~/k/vmlinux write_sysrq_trigger+0x51/0x60
> >   write_sysrq_trigger+0x51/0x60:
> >   write_sysrq_trigger at drivers/tty/sysrq.c:1098
> > 
> > Or gdb can be used:
> > 
> >   $ echo "list *write_sysrq_trigger+0x51" |gdb ~/k/vmlinux |grep "is in"
> >   (gdb) 0xffffffff815b5d83 is in driver_probe_device (/home/jpoimboe/git/linux/drivers/base/dd.c:378).
> > 
> > (But note that when there are duplicate symbol names, gdb will only show
> > the first symbol it finds.  faddr2line is recommended over gdb because
> > it handles duplicates and it also does function size checking.)
> 
> The commit breaks scripts/decode_stacktrace.sh.
> 
> Not sure if it's possible to fix it only on decode_stacktrace.sh side: we
> seems don't have a way to clearly distinguish stack trace line of any
> other.

How about this bash regex?  Seems to work for me with no false
positives.

  [[ $line =~ [^+\ ]+\+0x[0-9a-f]+/0x[0-9a-f]+ ]]

-- 
Josh