On Tue 2026-09-08 12:17:44, [email protected] 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 <[email protected]> > > 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. [1] https://lore.kernel.org/all/[email protected]/ Best Regards, Petr > > + } > > + } > > + > > ret = kallsyms_lookup_size_offset((unsigned long)func->old_func, > > -- > Sashiko AI review ยท > https://sashiko.dev/#/patchset/[email protected]?part=1
