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Subject[PATCH v10 10/14] module: kallsyms: Fix suspicious rcu usage
Date
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>
---
kernel/module/kallsyms.c | 34 ++++++++++++++++++++++------------
1 file changed, 22 insertions(+), 12 deletions(-)

diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index 1b0780e20aab..a3da0686a2a6 100644
--- 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];

--
2.34.1
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