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kallsyms: Disable preemption for find_kallsyms_symbol_value

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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: 31bf1dbccfb0 ("bpf: Fix attaching fentry/fexit/fmod_ret/lsm to modules")
Reported-by: Artem Savkov <asavkov@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Artem Savkov <asavkov@redhat.com>
Reviewed-by: Zhen 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/
This commit is contained in:
Jiri Olsa 2023-04-04 00:02:54 +02:00 committed by Andrii Nakryiko
parent e8f59d84f4
commit d099f594ad
1 changed files with 13 additions and 3 deletions
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16
kernel/module/kallsyms.c
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@ -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),