Re: [PATCH v5 4/6] livepatch: reuse module loader code to write relocations

Miroslav Benes
2016-03-21T13:55:55Z

On Wed, 16 Mar 2016, Jessica Yu wrote:

[...]

> +struct klp_buf {
> + char symname[KSYM_SYMBOL_LEN];

I think it is better to make this KSYM_NAME_LEN. KSYM_SYMBOL_LEN looks
like something different and KSYM_NAME_LEN is 128 which you reference
below.

> + char objname[MODULE_NAME_LEN];
> +};

[...]

> +static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod)
> +{
> + int i, cnt, vmlinux, ret;
> + struct klp_buf bufs = {0};
> + Elf_Rela *relas;
> + Elf_Sym *sym;
> + char *symname;
> + unsigned long sympos;
> +
> + relas = (Elf_Rela *) relasec->sh_addr;
> + /* For each rela in this klp relocation section */
> + for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
> + sym = pmod->core_kallsyms.symtab + ELF_R_SYM(relas[i].r_info);
> + if (sym->st_shndx != SHN_LIVEPATCH)
> + return -EINVAL;
> +
> + klp_clear_buf(&bufs);
> +
> + /* Format: .klp.sym.objname.symbol_name,sympos */
> + symname = pmod->core_kallsyms.strtab + sym->st_name;
> + cnt = sscanf(symname, ".klp.sym.%64[^.].%128[^,],%lu",
> + bufs.objname, bufs.symname, &sympos);

It would be really nice to change actual values for their macro
definitions, but this would be a mess which is not worth it. Anyway
shouldn't those width modifiers be %63 and %127 to make a room for \0?

> + if (cnt != 3)
> + return -EINVAL;
> +
> + /* klp_find_object_symbol() treats a NULL objname as vmlinux */
> + vmlinux = !strcmp(bufs.objname, "vmlinux");
> + ret = klp_find_object_symbol(vmlinux ? NULL : bufs.objname,
> + bufs.symname, sympos,
> + (unsigned long *) &sym->st_value);
> + if (ret)
> + return ret;
> }
> - preempt_enable();
>
> - /*
> - * Check if it's in another .o within the patch module. This also
> - * checks that the external symbol is unique.
> - */
> - return klp_find_object_symbol(pmod->name, name, 0, addr);
> + return 0;
> }
>
> static int klp_write_object_relocations(struct module *pmod,
> struct klp_object *obj)
> {
> - int ret = 0;
> - unsigned long val;
> - struct klp_reloc *reloc;
> + int i, cnt, ret = 0;
> + const char *objname, *secname;
> + struct klp_buf bufs = {0};
> + Elf_Shdr *sec;
>
> if (WARN_ON(!klp_is_object_loaded(obj)))
> return -EINVAL;
>
> - if (WARN_ON(!obj->relocs))
> - return -EINVAL;
> + objname = klp_is_module(obj) ? obj->name : "vmlinux";
>
> module_disable_ro(pmod);
> + /* For each klp relocation section */
> + for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
> + sec = pmod->klp_info->sechdrs + i;
> + if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
> + continue;
>
> - for (reloc = obj->relocs; reloc->name; reloc++) {
> - /* discover the address of the referenced symbol */
> - if (reloc->external) {
> - if (reloc->sympos > 0) {
> - pr_err("non-zero sympos for external reloc symbol '%s' is not supported\n",
> - reloc->name);
> - ret = -EINVAL;
> - goto out;
> - }
> - ret = klp_find_external_symbol(pmod, reloc->name, &val);
> - } else
> - ret = klp_find_object_symbol(obj->name,
> - reloc->name,
> - reloc->sympos,
> - &val);
> - if (ret)
> - goto out;
> + klp_clear_buf(&bufs);
>
> - ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
> - val + reloc->addend);
> - if (ret) {
> - pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
> - reloc->name, val, ret);
> - goto out;
> + /* Check if this klp relocation section belongs to obj */
> + secname = pmod->klp_info->secstrings + sec->sh_name;
> + cnt = sscanf(secname, ".klp.rela.%64[^.]", bufs.objname);

Same here.

Otherwise it looks really good (which applies for the whole series), so
after fixing these nits you can add my

Reviewed-by: Miroslav Benes <mbenes@suse.cz>

Cheers,
Miroslav