From: Al Viro Date: Wed, 2 Jun 2021 03:53:14 +0000 (+1000) Subject: x86: signal: don't do sas_ss_reset() until we are certain that sigframe won't be... X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=3d21a4046b1cda00fbfc386ee9dfd292c2e075b8;p=users%2Fjedix%2Flinux-maple.git x86: signal: 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(). Link: https://lore.kernel.org/lkml/20200404170604.GN23230@ZenIV.linux.org.uk/ Link: https://github.com/ClangBuiltLinux/linux/issues/876 Link: https://lkml.kernel.org/r/20210422230846.1756380-1-ndesaulniers@google.com Signed-off-by: Al Viro Signed-off-by: Nick Desaulniers Acked-by: Oleg Nesterov Tested-by: Nathan Chancellor Signed-off-by: Andrew Morton Signed-off-by: Stephen Rothwell --- diff --git a/include/linux/compat.h b/include/linux/compat.h index 8855b1b702b2a..c270124e44020 100644 --- a/include/linux/compat.h +++ b/include/linux/compat.h @@ -532,8 +532,6 @@ 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 201f88e3738b2..2b22da56c5f95 100644 --- a/include/linux/signal.h +++ b/include/linux/signal.h @@ -463,8 +463,6 @@ 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 f7c6ffcbd0440..56b6e96343165 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2869,6 +2869,8 @@ 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); } @@ -4187,11 +4189,7 @@ 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 @@ -4246,11 +4244,7 @@ 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