On Wed, 2 Oct 2019, Petr Mladek wrote:
> On Thu 2019-09-05 14:45:12, Miroslav Benes wrote:
> > We thus decided to reverse the relocation patching (clear all relocation
> > targets on x86_64, or return back nops on powerpc). The solution is not
> > universal and is too much arch-specific, but it may prove to be simpler
> > in the end.
> >
> > diff --git a/arch/powerpc/kernel/module_64.c
> > b/arch/powerpc/kernel/module_64.c
> > index a93b10c48000..e461d456e447 100644
> > --- a/arch/powerpc/kernel/module_64.c
> > +++ b/arch/powerpc/kernel/module_64.c
> > @@ -741,6 +741,51 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> > return 0;
> > }
> >
> > +#ifdef CONFIG_LIVEPATCH
> > +void clear_relocate_add(Elf64_Shdr *sechdrs,
> > + const char *strtab,
> > + unsigned int symindex,
> > + unsigned int relsec,
> > + struct module *me)
> > +{
> > + unsigned int i;
> > + Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr;
> > + Elf64_Sym *sym;
> > + unsigned long *location;
> > + const char *symname;
> > + u32 *instruction;
> > +
> > + pr_debug("Applying ADD relocate section %u to %u\n", relsec,
>
> s/Applying/Clearing/
Ugh. Thanks for noticing.
> > + sechdrs[relsec].sh_info);
> > +
> > + for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rela); i++) {
> > + location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
> > + + rela[i].r_offset;
> > + sym = (Elf64_Sym *)sechdrs[symindex].sh_addr
> > + + ELF64_R_SYM(rela[i].r_info);
> > + symname = me->core_kallsyms.strtab
> > + + sym->st_name;
> > +
> > + if (ELF64_R_TYPE(rela[i].r_info) != R_PPC_REL24)
> > + continue;
>
> I expected that the code below would reverse the operations
> in apply_relocate_add() for case R_PPC_REL24. But it is not
> obvious for me.
It should, but it is not obvious. See restore_r2(). We only need to
replace PPC_INST_LD_TOC instruction with PPC_INST_NOP and that's it.
> It might be because I am not familiar with the code. Or would
> it deserve some comments?
Maybe.
> > +
> > + if (sym->st_shndx != SHN_UNDEF &&
> > + sym->st_shndx != SHN_LIVEPATCH)
> > + continue;
> > +
> > + instruction = (u32 *)location;
> > + if (is_mprofile_mcount_callsite(symname, instruction))
> > + continue;
> > +
> > + if (!instr_is_relative_link_branch(*instruction))
> > + continue;
> > +
> > + instruction += 1;
> > + *instruction = PPC_INST_NOP;
> > + }
> > +}
> > +#endif
> > +
> > #ifdef CONFIG_DYNAMIC_FTRACE
> >
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index ab4a4606d19b..f0b380d2a17a 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> > @@ -295,6 +295,45 @@ static int klp_write_object_relocations(struct module
> > *pmod,
> > return ret;
> > }
> >
> > +static void klp_clear_object_relocations(struct module *pmod,
> > + struct klp_object *obj)
> > +{
> > + int i, cnt;
> > + const char *objname, *secname;
> > + char sec_objname[MODULE_NAME_LEN];
> > + Elf_Shdr *sec;
> > +
> > + objname = klp_is_module(obj) ? obj->name : "vmlinux";
> > +
> > + /* For each klp relocation section */
> > + for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
> > + sec = pmod->klp_info->sechdrs + i;
> > + secname = pmod->klp_info->secstrings + sec->sh_name;
> > + if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
> > + continue;
> > +
> > + /*
> > + * Format: .klp.rela.sec_objname.section_name
> > + * See comment in klp_resolve_symbols() for an explanation
> > + * of the selected field width value.
> > + */
> > + secname = pmod->klp_info->secstrings + sec->sh_name;
> > + cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
> > + if (cnt != 1) {
> > + pr_err("section %s has an incorrectly formatted name\n",
> > + secname);
> > + continue;
> > + }
> > +
> > + if (strcmp(objname, sec_objname))
> > + continue;
> > +
>
> It would make the review easier when the order of 1st and 2nd
> patch was swaped. I mean that I would not need to check twice
> that the two functions actually share the same code.
Ok.
> > + clear_relocate_add(pmod->klp_info->sechdrs,
> > + pmod->core_kallsyms.strtab,
> > + pmod->klp_info->symndx, i, pmod);
> > + }
> > +}
> > +
> > /*
> > * Sysfs Interface
> > *
>
> I was not able to check correctness of the ppc and s390 parts.
> Otherwise, it looks good to me.
Thanks
Miroslav
