Re: [PATCH v4 1/5] livepatch: Fail object initialization on duplicate patched function

[Miroslav Benes]

On Tue, 8 Sep 2026, Petr Mladek wrote:

> On Tue 2026-09-08 12:17:44, sashiko-bot@xxxxxxxxxx wrote:
> > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> > - [High] Atomic replace patches will fail to load if previous patches targeted aliased functions.
> > --
> > 
> > commit e5553650270f93e11fe885d264a3829802223d3a
> > Author: Harry Hsu <x90613@xxxxxxxxx>
> > 
> > livepatch: Fail object initialization on duplicate patched function
> > 
> > This commit introduces a check to prevent patching multiple aliases of a
> > function within a single livepatch. It fails object initialization if aliases
> > resolving to the same address are detected.
> > 
> > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > > index a240d1144e89c..a6762cbe74b70 100644
> > > --- a/kernel/livepatch/core.c
> > > +++ b/kernel/livepatch/core.c
> > [ ... ]
> > > @@ -885,6 +885,21 @@ static int klp_init_object_loaded(struct klp_patch *patch,
> > >  		if (ret)
> > >  			return ret;
> > >  
> > > +		/*
> > > +		 * Aliased symbols share one address, so they would resolve to
> > > +		 * the same klp_ops and stack up on a single ops->func_stack,
> > > +		 * leaving the redirection ambiguous.
> > > +		 */
> > > +		klp_for_each_func(obj, prev_func) {
> > > +			if (prev_func == func)
> > > +				break;
> > > +			if (prev_func->old_func == func->old_func) {
> > > +				pr_err("'%s' and '%s' resolve to the same address, aliased symbols are not supported\n",
> > > +				       prev_func->old_name, func->old_name);
> > > +				return -EINVAL;
> > 
> > [Severity: High]
> > Will this check inadvertently reject nop functions generated by an atomic
> > replace patch when previous patches targeted aliased functions?
> > 
> > If previously loaded livepatches targeted aliased functions (for example, one
> > patch targets __do_sys_fork and another targets __x64_sys_fork), they were
> > permitted since they resided in different patches.
> > 
> > When an atomic replace patch is loaded, klp_add_nops() loops over all
> > previously patched functions and adds nops for them to the new patch. Since
> > nop deduplication is based on old_name, nops for both aliases are added.
> > 
> > Later, this check in klp_init_object_loaded() resolves their addresses and
> > finds duplicate old_func addresses. This causes the initialization to fail
> > with -EINVAL, which prevents the system from atomically replacing existing
> > livepatches and might force a reboot if the old patches cannot be safely
> > disabled manually.
> 
> Wow, this is a nice catch. I would say that it is a corner case but
> the problem seems to exist. Now, the question is how to deal with it.
> 
> I see three possibilities:
> 
> 1. We might detect the aliases in klp_find_func() and create only
>    one "nop" entry or do not create it all.
> 
> 2. The problem might be easier to solve after adding
>    the provides/obsoletes, aka replace set, feature [1].
>    It should prevent loading the other livepatch for the aliased
>    symbol in the 1st place.
> 
> 3. Just document the problem as a limitation. It might be hit only
>    when installing more liveapatches in parallel that current
>    wild way.
> 
> I personally prefer to wait for the provides/requires feature.

Perhaps.

Could we also check prev_func/func->nop in the check in 
klp_init_object_loaded() and have a pass if true?

Miroslav