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) 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 index 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 ` 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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