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From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Petr Mladek <pmladek@suse.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	rostedt@goodmis.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,
	jeyu@kernel.org, live-patching@vger.kernel.org,
	Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH v4 15/16] module: Move where we mark modules RO,X
Date: Mon, 28 Oct 2019 11:07:21 +0100	[thread overview]
Message-ID: <20191028100721.GK4131@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20191026011741.xywerjv62vdmz6sp@treble>

On Fri, Oct 25, 2019 at 08:17:41PM -0500, Josh Poimboeuf wrote:

> + *    The following restrictions apply to module-specific relocation sections:
> + *
> + *    a) References to vmlinux symbols are not allowed.  Otherwise there might
> + *       be module init ordering issues, and crashes might occur in some of the
> + *       other kernel patching components like paravirt patching or jump
> + *       labels.  All references to vmlinux symbols should use either normal
> + *       relas (for exported symbols) or vmlinux-specific klp relas (for
> + *       unexported symbols).  This restriction is enforced in
> + *       klp_resolve_symbols().

Right.

> + *    b) Relocations to special sections like __jump_table and .altinstructions
> + *       aren't allowed.  In other words, there should never be a
> + *       .klp.rela.{module}.__jump_table section.  This will definitely cause
> + *       initialization ordering issues, as such special sections are processed
> + *       during the loading of the klp module itself, *not* the to-be-patched
> + *       module.  This means that e.g., it's not currently possible to patch a
> + *       module function which uses a static key jump label, if you want to
> + *       have the replacement function also use the same static key.  In this
> + *       case, a non-static interface like static_key_enabled() can be used in
> + *       the new function instead.

Idem for .static_call_sites I suppose..

Is there any enforcement on this? I'm thinking it should be possible to
detect the presence of these sections and yell a bit.

OTOH, it should be possible to actually handle this, but let's do that
later.

> + *       On the other hand, a .klp.rela.vmlinux.__jump_table section is fine,
> + *       as it can be resolved early enough during the load of the klp module,
> + *       as described above.
> + */

> diff --git a/kernel/module.c b/kernel/module.c
> index fe5bd382759c..ff4347385f05 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2327,11 +2327,9 @@ static int apply_relocations(struct module *mod, const struct load_info *info)
>  		if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC))
>  			continue;
>  
> -		/* Livepatch relocation sections are applied by livepatch */
>  		if (info->sechdrs[i].sh_flags & SHF_RELA_LIVEPATCH)
> -			continue;
> -
> -		if (info->sechdrs[i].sh_type == SHT_REL)
> +			err = klp_write_relocations(mod, NULL);
> +		else if (info->sechdrs[i].sh_type == SHT_REL)
>  			err = apply_relocate(info->sechdrs, info->strtab,
>  					     info->index.sym, i, mod);
>  		else if (info->sechdrs[i].sh_type == SHT_RELA)

Like here, we can yell and error if .klp.rela.{mod}.__jump_table
sections are encountered.


Other than that, this should work I suppose.

  reply	other threads:[~2019-10-28 10:07 UTC|newest]

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-18  7:35 [PATCH v4 00/16] Rewrite x86/ftrace to use text_poke (and more) Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 01/16] x86/alternatives: Teach text_poke_bp() to emulate instructions Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 02/16] x86/alternatives: Update int3_emulate_push() comment Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 03/16] x86/alternatives,jump_label: Provide better text_poke() batching interface Peter Zijlstra
2019-10-21  8:48   ` Ingo Molnar
2019-10-21  9:21     ` Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 04/16] x86/alternatives: Add and use text_gen_insn() helper Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 05/16] x86/ftrace: Use text_poke() Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 06/16] x86/mm: Remove set_kernel_text_r[ow]() Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 07/16] x86/alternative: Add text_opcode_size() Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 08/16] x86/ftrace: Use text_gen_insn() Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 09/16] x86/alternative: Remove text_poke_loc::len Peter Zijlstra
2019-10-21  8:58   ` Ingo Molnar
2019-10-21  9:02     ` Ingo Molnar
2019-10-18  7:35 ` [PATCH v4 10/16] x86/alternative: Shrink text_poke_loc Peter Zijlstra
2019-10-21  9:01   ` Ingo Molnar
2019-10-21  9:25     ` Peter Zijlstra
2019-10-21  9:33       ` Ingo Molnar
2019-10-18  7:35 ` [PATCH v4 11/16] x86/kprobes: Convert to text-patching.h Peter Zijlstra
2019-10-21 14:57   ` Masami Hiramatsu
2019-10-18  7:35 ` [PATCH v4 12/16] x86/kprobes: Fix ordering Peter Zijlstra
2019-10-22  1:35   ` Masami Hiramatsu
2019-10-22 10:31     ` Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 13/16] arm/ftrace: Use __patch_text_real() Peter Zijlstra
2019-10-28 16:25   ` Will Deacon
2019-10-28 16:34     ` Peter Zijlstra
2019-10-28 16:35       ` Peter Zijlstra
2019-10-28 16:47       ` Will Deacon
2019-10-28 16:55         ` Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 14/16] module: Remove set_all_modules_text_*() Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 15/16] module: Move where we mark modules RO,X Peter Zijlstra
2019-10-21 13:53   ` Josh Poimboeuf
2019-10-21 14:14     ` Peter Zijlstra
2019-10-21 15:34       ` Peter Zijlstra
2019-10-21 15:44         ` Peter Zijlstra
2019-10-21 16:11         ` Peter Zijlstra
2019-10-22 11:31           ` Heiko Carstens
2019-10-22 12:31             ` Peter Zijlstra
2019-10-23 11:48       ` Peter Zijlstra
2019-10-23 15:16         ` Peter Zijlstra
2019-10-23 17:15           ` Josh Poimboeuf
2019-10-24 10:59             ` Peter Zijlstra
2019-10-24 18:31               ` Josh Poimboeuf
2019-10-24 20:33                 ` Peter Zijlstra
2019-10-23 17:00         ` Josh Poimboeuf
2019-10-24 13:16           ` Peter Zijlstra
2019-10-25  6:44             ` Petr Mladek
2019-10-25  8:43               ` Peter Zijlstra
2019-10-25 10:06                 ` Peter Zijlstra
2019-10-25 13:50                   ` Josh Poimboeuf
2019-10-26  1:17                   ` Josh Poimboeuf
2019-10-28 10:07                     ` Peter Zijlstra [this message]
2019-10-28 10:43                     ` Peter Zijlstra
2019-10-25  9:16               ` Peter Zijlstra
2019-10-22  2:21   ` Steven Rostedt
2019-10-22 20:24     ` Peter Zijlstra
2019-10-22 20:40       ` Steven Rostedt
2019-10-23  9:07         ` Peter Zijlstra
2019-10-23 18:52       ` Steven Rostedt
2019-10-24 10:16         ` Peter Zijlstra
2019-10-24 10:18           ` Peter Zijlstra
2019-10-24 15:00           ` Steven Rostedt
2019-10-24 16:43             ` Peter Zijlstra
2019-10-24 18:17               ` Steven Rostedt
2019-10-24 20:24                 ` Peter Zijlstra
2019-10-24 20:28                   ` Steven Rostedt
2019-10-18  7:35 ` [PATCH v4 16/16] ftrace: Merge ftrace_module_{init,enable}() Peter Zijlstra
2019-10-18  8:20   ` Peter Zijlstra
2019-10-21  9:09 ` [PATCH v4 00/16] Rewrite x86/ftrace to use text_poke (and more) Ingo Molnar
2019-10-21 13:38   ` Steven Rostedt

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