Messages in this thread |  | | From | Nick Desaulniers <> | Date | Mon, 13 Apr 2020 12:12:58 -0700 | Subject | Re: [PATCH v2] x86: signal: move save_altstack_ex out of generic headers |
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On Sat, Apr 4, 2020 at 10:06 AM Al Viro <viro@zeniv.linux.org.uk> wrote: > > On Sat, Apr 04, 2020 at 06:01:00PM +0200, Oleg Nesterov wrote: > > On 04/03, Nick Desaulniers wrote: > > > > > > --- a/arch/x86/kernel/signal.c > > > +++ b/arch/x86/kernel/signal.c > > > @@ -416,6 +416,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig, > > > return 0; > > > Efault: > > > user_access_end(); > > > + reset_altstack(); > > > return -EFAULT; > > > } > > > #else /* !CONFIG_X86_32 */ > > > @@ -507,6 +508,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig, > > > > > > Efault: > > > user_access_end(); > > > + reset_altstack(); > > > return -EFAULT; > > > } > > > > I must have missed something, but this looks just wrong. > > > > reset_altstack() should be called when __setup_rt_frame() (and > > unsafe_save_altstack() in particular) succeeds, not when it fails. > > > > Nevermind, Al has already suggested to use signal_delivered()... > > FWIW, I propose to do is the patch below (against the current mainline); > objections? > > Don't do sas_ss_reset() until we are certain that sigframe won't be abandoned > > Currently we handle SS_AUTODISARM as soon as we have stored the > altstack settings into sigframe - that's the point when we have > set the things up for eventual sigreturn to restore the old settings. > And if we manage to set the sigframe up (we are not done with that > yet), everything's fine. However, in case of failure we end up > with sigframe-to-be abandoned and SIGSEGV force-delivered. And > in that case we end up with inconsistent rules - late failures > have altstack reset, early ones do not. > > It's trivial to get consistent behaviour - just handle SS_AUTODISARM > once we have set the sigframe up and are committed to entering > the handler, i.e. in signal_delivered(). > > Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Nick Desaulniers <ndesaulniers@google.com> I'll follow up on our KASAN implementation turning two consecutive longs into memset, which is odd. Some of the recent changes to unsafe_put_user to pass a label are triggering new error: inline assembly requires more registers than available in arch/x86/ia32/ia32_signal.c for me, but they're unrelated to this patch.
> --- > diff --git a/include/linux/compat.h b/include/linux/compat.h > index 0480ba4db592..f614967374f5 100644 > --- a/include/linux/compat.h > +++ b/include/linux/compat.h > @@ -461,8 +461,6 @@ int __compat_save_altstack(compat_stack_t __user *, unsigned long); > &__uss->ss_sp, label); \ > unsafe_put_user(t->sas_ss_flags, &__uss->ss_flags, label); \ > unsafe_put_user(t->sas_ss_size, &__uss->ss_size, label); \ > - if (t->sas_ss_flags & SS_AUTODISARM) \ > - sas_ss_reset(t); \ > } while (0); > > /* > diff --git a/include/linux/signal.h b/include/linux/signal.h > index 05bacd2ab135..28fe9cc134f7 100644 > --- a/include/linux/signal.h > +++ b/include/linux/signal.h > @@ -450,8 +450,6 @@ int __save_altstack(stack_t __user *, unsigned long); > unsafe_put_user((void __user *)t->sas_ss_sp, &__uss->ss_sp, label); \ > unsafe_put_user(t->sas_ss_flags, &__uss->ss_flags, label); \ > unsafe_put_user(t->sas_ss_size, &__uss->ss_size, label); \ > - if (t->sas_ss_flags & SS_AUTODISARM) \ > - sas_ss_reset(t); \ > } while (0); > > #ifdef CONFIG_PROC_FS > diff --git a/kernel/signal.c b/kernel/signal.c > index e58a6c619824..4cfe0b9af588 100644 > --- a/kernel/signal.c > +++ b/kernel/signal.c > @@ -2769,6 +2769,8 @@ static void signal_delivered(struct ksignal *ksig, int stepping) > if (!(ksig->ka.sa.sa_flags & SA_NODEFER)) > sigaddset(&blocked, ksig->sig); > set_current_blocked(&blocked); > + if (current->sas_ss_flags & SS_AUTODISARM) > + sas_ss_reset(current); > tracehook_signal_handler(stepping); > } > > @@ -4070,11 +4072,7 @@ int __save_altstack(stack_t __user *uss, unsigned long sp) > int err = __put_user((void __user *)t->sas_ss_sp, &uss->ss_sp) | > __put_user(t->sas_ss_flags, &uss->ss_flags) | > __put_user(t->sas_ss_size, &uss->ss_size); > - if (err) > - return err; > - if (t->sas_ss_flags & SS_AUTODISARM) > - sas_ss_reset(t); > - return 0; > + return err; > } > > #ifdef CONFIG_COMPAT > @@ -4129,11 +4127,7 @@ int __compat_save_altstack(compat_stack_t __user *uss, unsigned long sp) > &uss->ss_sp) | > __put_user(t->sas_ss_flags, &uss->ss_flags) | > __put_user(t->sas_ss_size, &uss->ss_size); > - if (err) > - return err; > - if (t->sas_ss_flags & SS_AUTODISARM) > - sas_ss_reset(t); > - return 0; > + return err; > } > #endif >
-- Thanks, ~Nick Desaulniers
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