linux-kernel - Re: [PATCH 1/7] livepatch: Apply vmlinux-specific KLP relocations early

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Message-ID: <20200414193150.iqw224itgpedpltm@treble>
Date:   Tue, 14 Apr 2020 14:31:50 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jessica Yu <jeyu@...nel.org>
Subject: Re: [PATCH 1/7] livepatch: Apply vmlinux-specific KLP relocations
 early

On Tue, Apr 14, 2020 at 01:01:09PM -0500, Josh Poimboeuf wrote:
> On Tue, Apr 14, 2020 at 07:44:06PM +0200, Peter Zijlstra wrote:
> > On Tue, Apr 14, 2020 at 11:28:37AM -0500, Josh Poimboeuf wrote:
> > > KLP relocations are livepatch-specific relocations which are applied to
> > >   1) vmlinux-specific KLP relocation sections
> > > 
> > >      .klp.rela.vmlinux.{sec}
> > > 
> > >      These are relocations (applied to the KLP module) which reference
> > >      unexported vmlinux symbols.
> > > 
> > >   2) module-specific KLP relocation sections
> > > 
> > >      .klp.rela.{module}.{sec}:
> > > 
> > >      These are relocations (applied to the KLP module) which reference
> > >      unexported or exported module symbols.
> > 
> > Is there something that disallows a module from being called 'vmlinux' ?
> > If not, we might want to enforce this somewhere.
> 
> I'm pretty sure we don't have a check for that anywhere, though the KLP
> module would almost certainly fail during the module load when it
> couldn't find the vmlinux.ko symbols it needed.
> 
> It wouldn't hurt to add a check somewhere though.  Maybe in
> klp_module_coming() since the restriction only applies to
> CONFIG_LIVEPATCH...

From: Josh Poimboeuf <jpoimboe@...hat.com>
Subject: [PATCH] livepatch: Disallow vmlinux.ko

This is purely a theoretical issue, but if there were a module named
vmlinux.ko, the livepatch relocation code wouldn't be able to
distinguish between vmlinux-specific and vmlinux.o-specific KLP
relocations.

If CONFIG_LIVEPATCH is enabled, don't allow a module named vmlinux.ko.

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 kernel/livepatch/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 3a88639b3326..3ff886b911ae 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -1169,6 +1169,11 @@ int klp_module_coming(struct module *mod)
 	if (WARN_ON(mod->state != MODULE_STATE_COMING))
 		return -EINVAL;
 
+	if (!strcmp(mod->name, "vmlinux")) {
+		pr_err("vmlinux.ko: invalid module name");
+		return -EINVAL;
+	}
+
 	mutex_lock(&klp_mutex);
 	/*
 	 * Each module has to know that klp_module_coming()
-- 
2.21.1