Messages in this thread Patch in this message | | | Date | Thu, 22 Apr 2021 16:08:37 -0700 | Subject | [PATCH] x86: signal: Don't do sas_ss_reset() until we are certain that sigframe won't be abandoned | From | Nick Desaulniers <> |
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From: Al Viro <viro@zeniv.linux.org.uk>
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 Acked-by: Oleg Nesterov <oleg@redhat.com> Tested-by: Nathan Chancellor <natechancellor@gmail.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> --- include/linux/compat.h | 2 -- include/linux/signal.h | 2 -- kernel/signal.c | 14 ++++---------- 3 files changed, 4 insertions(+), 14 deletions(-)
diff --git a/include/linux/compat.h b/include/linux/compat.h index 6e65be753603..40ad060deb82 100644 --- a/include/linux/compat.h +++ b/include/linux/compat.h @@ -494,8 +494,6 @@ 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 205526c4003a..20887ff4c27a 100644 --- a/include/linux/signal.h +++ b/include/linux/signal.h @@ -460,8 +460,6 @@ 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 f2718350bf4b..384030909daf 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2815,6 +2815,8 @@ 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); } @@ -4133,11 +4135,7 @@ 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 @@ -4192,11 +4190,7 @@ 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 base-commit: 16fc44d6387e260f4932e9248b985837324705d8 -- 2.31.1.498.g6c1eba8ee3d-goog
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