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From: Mark Brown <>
To: Josh Poimboeuf <>
Cc:, Mark Rutland <>,
	Jiri Kosina <>,
	Joe Lawrence <>,
	Jonathan Corbet <>, Miroslav Benes <>,
	Petr Mladek <>,,
Subject: Re: [PATCH] Documentation: livepatch: document reliable stacktrace
Date: Wed, 13 Jan 2021 20:23:15 +0000	[thread overview]
Message-ID: <> (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

> 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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  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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