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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
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 index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20191018073525.768931536@infradead.org>
     [not found] ` <20191018074634.801435443@infradead.org>
     [not found]   ` <20191021135312.jbbxsuipxldocdjk@treble>
     [not found]     ` <20191021141402.GI1817@hirez.programming.kicks-ass.net>
     [not found]       ` <20191023114835.GT1817@hirez.programming.kicks-ass.net>
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

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