From 97c885d585c53d3f1ad4545b0ee10f0bdfaa1a4d Mon Sep 17 00:00:00 2001 From: Al Viro Date: Wed, 30 Jun 2021 18:56:43 -0700 Subject: 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: Linus Torvalds --- kernel/signal.c | 14 ++++---------- 1 file changed, 4 insertions(+), 10 deletions(-) (limited to 'kernel/signal.c') diff --git a/kernel/signal.c b/kernel/signal.c index 30a0bee5ff9b..6b4df88cc630 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2829,6 +2829,8 @@ 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); } @@ -4147,11 +4149,7 @@ 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 @@ -4206,11 +4204,7 @@ 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 -- cgit v1.2.3