module: kallsyms: Fix suspicious rcu usage

No functional change.

The purpose of this patch is to address the various Sparse warnings
due to the incorrect dereference/or access of an __rcu pointer.

Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index 1b0780e..a3da068 100644 (file)
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@@ -171,14 +171,17 @@ void add_kallsyms(struct module *mod, const struct load_info *info)
        Elf_Shdr *symsec = &info->sechdrs[info->index.sym];
 
        /* Set up to point into init section. */
-       mod->kallsyms = mod->init_layout.base + info->mod_kallsyms_init_off;
+       mod->kallsyms = (void __rcu *)mod->init_layout.base +
+               info->mod_kallsyms_init_off;
 
+       preempt_disable();
        /* The following is safe since this pointer cannot change */
-       mod->kallsyms->symtab = (void *)symsec->sh_addr;
-       mod->kallsyms->num_symtab = symsec->sh_size / sizeof(Elf_Sym);
+       rcu_dereference_sched(mod->kallsyms)->symtab = (void *)symsec->sh_addr;
+       rcu_dereference_sched(mod->kallsyms)->num_symtab = symsec->sh_size / sizeof(Elf_Sym);
        /* Make sure we get permanent strtab: don't use info->strtab. */
-       mod->kallsyms->strtab = (void *)info->sechdrs[info->index.str].sh_addr;
-       mod->kallsyms->typetab = mod->init_layout.base + info->init_typeoffs;
+       rcu_dereference_sched(mod->kallsyms)->strtab =
+               (void *)info->sechdrs[info->index.str].sh_addr;
+       rcu_dereference_sched(mod->kallsyms)->typetab = mod->init_layout.base + info->init_typeoffs;
 
        /*
         * Now populate the cut down core kallsyms for after init
@@ -187,20 +190,22 @@ void add_kallsyms(struct module *mod, const struct load_info *info)
        mod->core_kallsyms.symtab = dst = mod->core_layout.base + info->symoffs;
        mod->core_kallsyms.strtab = s = mod->core_layout.base + info->stroffs;
        mod->core_kallsyms.typetab = mod->core_layout.base + info->core_typeoffs;
-       src = mod->kallsyms->symtab;
-       for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) {
-               mod->kallsyms->typetab[i] = elf_type(src + i, info);
+       src = rcu_dereference_sched(mod->kallsyms)->symtab;
+       for (ndst = i = 0; i < rcu_dereference_sched(mod->kallsyms)->num_symtab; i++) {
+               rcu_dereference_sched(mod->kallsyms)->typetab[i] = elf_type(src + i, info);
                if (i == 0 || is_livepatch_module(mod) ||
                    is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum,
                                   info->index.pcpu)) {
                        mod->core_kallsyms.typetab[ndst] =
-                           mod->kallsyms->typetab[i];
+                           rcu_dereference_sched(mod->kallsyms)->typetab[i];
                        dst[ndst] = src[i];
                        dst[ndst++].st_name = s - mod->core_kallsyms.strtab;
-                       s += strscpy(s, &mod->kallsyms->strtab[src[i].st_name],
+                       s += strscpy(s,
+                                    &rcu_dereference_sched(mod->kallsyms)->strtab[src[i].st_name],
                                     KSYM_NAME_LEN) + 1;
                }
        }
+       preempt_enable();
        mod->core_kallsyms.num_symtab = ndst;
 }
 
@@ -478,11 +483,16 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
 
        mutex_lock(&module_mutex);
        list_for_each_entry(mod, &modules, list) {
-               /* We hold module_mutex: no need for rcu_dereference_sched */
-               struct mod_kallsyms *kallsyms = mod->kallsyms;
+               struct mod_kallsyms *kallsyms;
 
                if (mod->state == MODULE_STATE_UNFORMED)
                        continue;
+
+               /* Use rcu_dereference_sched() to remain compliant with the sparse tool */
+               preempt_disable();
+               kallsyms = rcu_dereference_sched(mod->kallsyms);
+               preempt_enable();
+
                for (i = 0; i < kallsyms->num_symtab; i++) {
                        const Elf_Sym *sym = &kallsyms->symtab[i];