Messages in this thread | | | From | Arnd Bergmann <> | Date | Fri, 30 Aug 2019 12:44:24 +0200 | Subject | Re: objtool warning "uses BP as a scratch register" with clang-9 |
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On Fri, Aug 30, 2019 at 1:24 AM Josh Poimboeuf <jpoimboe@redhat.com> wrote: > On Wed, Aug 28, 2019 at 05:40:01PM +0200, Arnd Bergmann wrote: > > diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c > > index 8eb7193e158d..fd49d28abbc5 100644 > > --- a/arch/x86/kernel/signal.c > > +++ b/arch/x86/kernel/signal.c > > @@ -414,6 +414,9 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig, > > */ > > put_user_ex(*((u64 *)&rt_retcode), (u64 *)frame->retcode); > > } put_user_catch(err); > > + > > + if (current->sas_ss_flags & SS_AUTODISARM) > > + sas_ss_reset(current); > > > > err |= copy_siginfo_to_user(&frame->info, &ksig->info); > > err |= setup_sigcontext(&frame->uc.uc_mcontext, fpstate,
> > diff --git a/include/linux/signal.h b/include/linux/signal.h > > index 67ceb6d7c869..9056239787f7 100644 > > --- a/include/linux/signal.h > > +++ b/include/linux/signal.h > > @@ -435,8 +435,6 @@ int __save_altstack(stack_t __user *, unsigned long); > > put_user_ex((void __user *)t->sas_ss_sp, &__uss->ss_sp); \ > > put_user_ex(t->sas_ss_flags, &__uss->ss_flags); \ > > put_user_ex(t->sas_ss_size, &__uss->ss_size); \ > > - if (t->sas_ss_flags & SS_AUTODISARM) \ > > - sas_ss_reset(t); \ > > } while (0); > > > > #ifdef CONFIG_PROC_FS > > Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Thanks! Before I submit this version for inclusion, let's make sure this is the best variant. I noticed later that save_altstack_ex() is meant to behave the same as __save_altstack(), but my patch breaks that assumption.
Two other alternatives I can think of are
- completely open-code save_altstack_ex() in its only call site on x86, in addition to the change above
- explicitly mark memset() as an exception in objtool in uaccess_safe_builtin[], assuming that is actually safe.
Arnd
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