From: Miroslav Benes <mbenes@suse.cz>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jessica Yu <jeyu@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Joe Lawrence <joe.lawrence@redhat.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
mhiramat@kernel.org, bristot@redhat.com, jbaron@akamai.com,
torvalds@linux-foundation.org, tglx@linutronix.de,
mingo@kernel.org, namit@vmware.com, hpa@zytor.com,
luto@kernel.org, ard.biesheuvel@linaro.org,
live-patching@vger.kernel.org, pmladek@suse.com
Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()
Date: Wed, 23 Oct 2019 11:04:04 +0200 (CEST) [thread overview]
Message-ID: <alpine.LSU.2.21.1910231057270.4266@pobox.suse.cz> (raw)
In-Reply-To: <20191022143107.xkymboxgcgojc5b5@treble>
On Tue, 22 Oct 2019, Josh Poimboeuf wrote:
> On Tue, Oct 22, 2019 at 10:27:49AM +0200, Miroslav Benes wrote:
> > > Does that sound like what you had in mind or am I totally off?
> >
> > Sort of. What I had in mind was that we could get rid of all special .klp
> > ELF section if module loader guarantees that only sections for loaded
> > modules are processed. Then .klp.rela.$objname is not needed and proper
> > .rela.text.$objname (or whatever its text section is named) should be
> > sufficient. The same for the rest (.klp.arch).
>
> If I understand correctly, using kvm as an example to-be-patched module,
> we'd have:
>
> .text.kvm
> .rela.text.kvm
> .altinstructions.kvm
> .rela.altinstructions.kvm
> __jump_table.kvm
> .rela__jump_table.kvm
>
> etc. i.e. any "special" sections would need to be renamed.
>
> Is that right?
Yes.
> But also I think *any* sections which need relocations would need to be
> renamed, for example:
>
> .rodata.kvm
> .rela.rodata.kvm
> .orc_unwind_ip.kvm
> .rela.orc_unwind_ip.kvm
Correct.
> It's an interesting idea.
>
> We'd have to be careful about ordering issues. For example, there are
> module-specific jump labels stored in mod->jump_entries. Right now
> that's just a pointer to the module's __jump_table section. With late
> module patching, when kvm is loaded we'd have to insert the klp module's
> __jump_table.kvm entries into kvm's mod->jump_entries list somehow.
Yes.
> Presumably we'd also have that issue for other sections. Handling that
> _might_ be as simple as just hacking up find_module_sections() to
> re-allocate sections and append "patched sections" to them.
>
> But then you still have to worry about when to apply the relocations.
> If you apply them before patching the sections, then relative
> relocations would have the wrong values. If you apply them after, then
> you have to figure out where the appended relocations are.
Ah, right. That is a valid remark.
> And if we allow unpatching then we'd presumably have to be able to
> remove entries from the module specific section lists.
Correct.
> So I get the feeling a lot of complexity would creep in. Even just
> thinking about it requires more mental gymnastics than the
> one-patch-per-module idea, so I view that as a bad sign.
Yes, the devil is in the details. It would be better if the approach
helped even someone/something else in the kernel. Without it, it is
probably better to stick to Steven's proposal and handle the complexity
elsewhere.
Thanks
Miroslav
next prev parent reply other threads:[~2019-10-23 9:04 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20191007081945.10951536.8@infradead.org>
[not found] ` <20191008104335.6fcd78c9@gandalf.local.home>
[not found] ` <20191009224135.2dcf7767@oasis.local.home>
[not found] ` <20191010092054.GR2311@hirez.programming.kicks-ass.net>
[not found] ` <20191010091956.48fbcf42@gandalf.local.home>
[not found] ` <20191010140513.GT2311@hirez.programming.kicks-ass.net>
[not found] ` <20191010115449.22044b53@gandalf.local.home>
[not found] ` <20191010172819.GS2328@hirez.programming.kicks-ass.net>
[not found] ` <20191011125903.GN2359@hirez.programming.kicks-ass.net>
[not found] ` <20191015130739.GA23565@linux-8ccs>
[not found] ` <20191015135634.GK2328@hirez.programming.kicks-ass.net>
2019-10-15 14:13 ` [PATCH v3 5/6] x86/ftrace: Use text_poke() Miroslav Benes
2019-10-15 15:06 ` Joe Lawrence
2019-10-15 15:31 ` Jessica Yu
2019-10-15 22:17 ` Joe Lawrence
2019-10-15 22:27 ` Steven Rostedt
2019-10-16 7:42 ` Peter Zijlstra
2019-10-16 10:15 ` Miroslav Benes
2019-10-21 15:05 ` Josh Poimboeuf
2020-01-20 16:50 ` Josh Poimboeuf
2020-01-21 8:35 ` Miroslav Benes
2020-01-21 16:10 ` Josh Poimboeuf
2020-01-22 10:09 ` Miroslav Benes
2020-01-22 21:42 ` Josh Poimboeuf
2020-01-28 9:28 ` Miroslav Benes
2020-01-28 15:00 ` Josh Poimboeuf
2020-01-28 15:40 ` Petr Mladek
2020-01-28 17:02 ` Josh Poimboeuf
2020-01-29 0:46 ` Jiri Kosina
2020-01-29 2:17 ` Josh Poimboeuf
2020-01-29 3:14 ` Jiri Kosina
2020-01-29 12:28 ` Miroslav Benes
2020-01-29 15:59 ` Josh Poimboeuf
2020-01-30 9:53 ` Petr Mladek
2020-01-30 14:17 ` Josh Poimboeuf
2020-01-31 7:17 ` Petr Mladek
2020-01-22 12:15 ` Miroslav Benes
2020-01-22 15:05 ` Miroslav Benes
2020-01-22 22:03 ` Josh Poimboeuf
2020-01-23 10:19 ` Martin Jambor
2019-10-16 7:49 ` Peter Zijlstra
2019-10-16 10:20 ` Miroslav Benes
2019-10-16 13:29 ` Miroslav Benes
2019-10-18 13:03 ` Jessica Yu
2019-10-18 13:40 ` Petr Mladek
2019-10-21 14:14 ` Jessica Yu
2019-10-21 15:31 ` Josh Poimboeuf
2019-10-22 8:27 ` Miroslav Benes
2019-10-22 14:31 ` Josh Poimboeuf
2019-10-23 9:04 ` Miroslav Benes [this message]
2019-10-16 6:51 ` Miroslav Benes
2019-10-16 9:23 ` Peter Zijlstra
2019-10-16 9:36 ` Jessica Yu
2019-10-16 9:51 ` Peter Zijlstra
2019-10-16 12:39 ` Peter Zijlstra
2019-10-22 8:45 ` Miroslav Benes
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