Commit d099f594 authored by Jiri Olsa's avatar Jiri Olsa Committed by Andrii Nakryiko
Browse files

kallsyms: Disable preemption for find_kallsyms_symbol_value 



Artem reported suspicious RCU usage [1]. The reason is that verifier
calls find_kallsyms_symbol_value with preemption enabled which will
trigger suspicious RCU usage warning in rcu_dereference_sched call.

Disabling preemption in find_kallsyms_symbol_value and adding
__find_kallsyms_symbol_value function.

Fixes: 31bf1dbc ("bpf: Fix attaching fentry/fexit/fmod_ret/lsm to modules")
Reported-by: default avatarArtem Savkov <asavkov@redhat.com>
Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Tested-by: default avatarArtem Savkov <asavkov@redhat.com>
Reviewed-by: default avatarZhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/bpf/20230403220254.2191240-1-jolsa@kernel.org

[1] https://lore.kernel.org/bpf/ZBrPMkv8YVRiWwCR@samus.usersys.redhat.com/
parent e8f59d84

kernel/module/kallsyms.c

+13 −3
Original line number Diff line number Diff line
@@ -442,7 +442,7 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type, 
}



/* Given a module and name of symbol, find and return the symbol's value */

unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name)

static unsigned long __find_kallsyms_symbol_value(struct module *mod, const char *name)

{

	unsigned int i;

	struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms);
@@ -466,7 +466,7 @@ static unsigned long __module_kallsyms_lookup_name(const char *name) 
	if (colon) {

		mod = find_module_all(name, colon - name, false);

		if (mod)

			return find_kallsyms_symbol_value(mod, colon + 1);

			return __find_kallsyms_symbol_value(mod, colon + 1);

		return 0;

	}
@@ -475,7 +475,7 @@ static unsigned long __module_kallsyms_lookup_name(const char *name) 


		if (mod->state == MODULE_STATE_UNFORMED)

			continue;

		ret = find_kallsyms_symbol_value(mod, name);

		ret = __find_kallsyms_symbol_value(mod, name);

		if (ret)

			return ret;

	}
@@ -494,6 +494,16 @@ unsigned long module_kallsyms_lookup_name(const char *name) 
	return ret;

}



unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name)

{

	unsigned long ret;



	preempt_disable();

	ret = __find_kallsyms_symbol_value(mod, name);

	preempt_enable();

	return ret;

}



int module_kallsyms_on_each_symbol(const char *modname,

				   int (*fn)(void *, const char *,

					     struct module *, unsigned long),