Messages in this thread Patch in this message | | | Date | Wed, 23 Oct 2019 17:16:54 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4 15/16] module: Move where we mark modules RO,X |
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On Wed, Oct 23, 2019 at 01:48:35PM +0200, Peter Zijlstra wrote: > On Mon, Oct 21, 2019 at 04:14:02PM +0200, Peter Zijlstra wrote: > > On Mon, Oct 21, 2019 at 08:53:12AM -0500, Josh Poimboeuf wrote: > > > > Doesn't livepatch code also need to be modified? We have: > > > > Urgh bah.. I was too focussed on the other klp borkage :/ But yes, > > arm64/ftrace and klp are the only two users of that function (outside of > > module.c) and Mark was already writing a patch for arm64. > > > > Means these last two patches need to wait a little until we've fixed > > those. > > So the other KLP issue: > > <mbenes> peterz: ad klp, apply_relocate_add() and text_poke()... what > about apply_alternatives() and apply_paravirt()? They call > text_poke_early(), which was ok with module_disable/enable_ro(), but > now it is not, I suppose. See arch_klp_init_object_loaded() in > arch/x86/kernel/livepatch.c. > > <peterz> mbenes: hurm, I don't see why we would need to do > apply_alternatives() / apply_paravirt() later, why can't we do that > the moment we load the module > > <peterz> mbenes: that is, those things _never_ change after boot > > <mbenes> peterz: as jpoimboe explained. See commit > d4c3e6e1b193497da3a2ce495fb1db0243e41e37 for detailed explanation. > > Now sadly that commit missed all the useful information, luckily I could > find the patch in my LKML folder, more sad, that thread still didn't > contain the actual useful information, for that I was directed to > github: > > https://github.com/dynup/kpatch/issues/580 > > Now, someone is owning me a beer for having to look at github for this. > > That finally explained that what happens is that the RELA was trying to > fix up the paravirt indirect call to 'local_irq_disable', which > apply_paravirt() will have overwritten with 'CLI; NOP'. This then > obviously goes *bang*. > > This then raises a number of questions: > > 1) why is that RELA (that obviously does not depend on any module) > applied so late? > > 2) why can't we unconditionally skip RELA's to paravirt sites? > > 3) Is there ever a possible module-dependent RELA to a paravirt / > alternative site? > > > Now, for 1), I would propose '.klp.rela.${mod}' sections only contain > RELAs that depend on symbols in ${mod} (or modules in general). We can > fix up RELAs that depend on core kernel early without problems. Let them > be in the normal .rela sections and be fixed up on loading the > patch-module as per usual. > > This should also deal with 2, paravirt should always have RELAs into the > core kernel. > > Then for 3) we only have alternatives left, and I _think_ it unlikely to > be the case, but I'll have to have a hard look at that. > > Hmmm ?
Something like so on top, I suppose.
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--- a/arch/x86/kernel/module.c +++ b/arch/x86/kernel/module.c @@ -131,7 +131,8 @@ static int __apply_relocate_add(Elf64_Sh unsigned int symindex, unsigned int relsec, struct module *me, - void *(*write)(void *addr, const void *val, size_t size)) + void *(*write)(void *addr, const void *val, size_t size), + bool klp) { unsigned int i; Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr; @@ -157,6 +158,14 @@ static int __apply_relocate_add(Elf64_Sh val = sym->st_value + rel[i].r_addend; + /* + * .klp.rela.* sections should only contain module + * related RELAs. All core-kernel RELAs should be in + * normal .rela.* sections and be applied when loading + * the patch module itself. + */ + WARN_ON_ONCE(klp && core_kernel_text(val)); + switch (ELF64_R_TYPE(rel[i].r_info)) { case R_X86_64_NONE: break; @@ -223,7 +232,7 @@ int apply_relocate_add(Elf64_Shdr *sechd unsigned int relsec, struct module *me) { - return __apply_relocate_add(sechdrs, strtab, symindex, relsec, me, memcpy); + return __apply_relocate_add(sechdrs, strtab, symindex, relsec, me, memcpy, false); } int klp_apply_relocate_add(Elf64_Shdr *sechdrs, @@ -234,7 +243,7 @@ int klp_apply_relocate_add(Elf64_Shdr *s { int ret; - ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me, text_poke); + ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me, text_poke, true); if (!ret) text_poke_sync();
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