From: Mark Brown <broonie@kernel.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: linux-kernel@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
Jiri Kosina <jikos@kernel.org>,
Joe Lawrence <joe.lawrence@redhat.com>,
Jonathan Corbet <corbet@lwn.net>, Miroslav Benes <mbenes@suse.cz>,
Petr Mladek <pmladek@suse.com>,
linux-doc@vger.kernel.org, live-patching@vger.kernel.org
Subject: Re: [PATCH] Documentation: livepatch: document reliable stacktrace
Date: Wed, 13 Jan 2021 20:23:15 +0000 [thread overview]
Message-ID: <20210113202315.GI4641@sirena.org.uk> (raw)
In-Reply-To: <20210113192735.rg2fxwlfrzueinci@treble>
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On Wed, Jan 13, 2021 at 01:33:13PM -0600, Josh Poimboeuf wrote:
> I think it's worth mentioning a little more about objtool. There are a
> few passing mentions of objtool's generation of metadata (i.e. ORC), but
> objtool has another relevant purpose: stack validation. That's
> particularly important when it comes to frame pointers.
> For some architectures like x86_64 and arm64 (but not powerpc/s390),
> it's far too easy for a human to write asm and/or inline asm which
> violates frame pointer protocol, silently causing the violater's callee
> to get skipped in the unwind. Such architectures need objtool
> implemented for CONFIG_STACK_VALIDATION.
This basically boils down to just adding a statement saying "you may
need to depend on objtool" I think?
> > +There are several ways an architecture may identify kernel code which is deemed
> > +unreliable to unwind from, e.g.
> > +* Using metadata created by objtool, with such code annotated with
> > + SYM_CODE_{START,END} or STACKFRAME_NON_STANDARD().
> I'm not sure why SYM_CODE_{START,END} is mentioned here, but it doesn't
> necessarily mean the code is unreliable, and objtool doesn't treat it as
> such. Its mention can probably be removed unless there was some other
> point I'm missing.
I was reading that as being a thing that the architecture could possibly
do, especially as a first step - it does seem like a reasonable thing to
consider using anyway. I guess you could also use it the other way
around and do additional checks for things that are supposed to be
regular functions that you relax for SYM_CODE() sections.
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next prev parent reply other threads:[~2021-01-13 20:24 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-13 16:57 [PATCH] Documentation: livepatch: document reliable stacktrace Mark Brown
2021-01-13 19:33 ` Josh Poimboeuf
2021-01-13 20:23 ` Mark Brown [this message]
2021-01-13 22:25 ` Josh Poimboeuf
2021-01-14 18:10 ` Mark Rutland
2021-01-15 0:03 ` Josh Poimboeuf
2021-01-14 11:54 ` Mark Rutland
2021-01-14 14:36 ` Josh Poimboeuf
2021-01-14 17:49 ` Mark Rutland
2021-01-14 20:03 ` Josh Poimboeuf
-- strict thread matches above, loose matches on Subject: below --
2020-10-23 15:35 Mark Rutland
2020-10-27 11:16 ` Petr Mladek
2020-10-29 10:04 ` Miroslav Benes
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