diff mbox series

[181/192] x86: signal: don't do sas_ss_reset() until we are certain that sigframe won't be abandoned

Message ID 20210701015643.SBUjrzC2l%akpm@linux-foundation.org (mailing list archive)
State New
Headers show
Series [001/192] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c | expand

Commit Message

Andrew Morton July 1, 2021, 1:56 a.m. UTC 
From: Al Viro <viro@zeniv.linux.org.uk>
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 <viro@zeniv.linux.org.uk>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/compat.h |    2 --
 include/linux/signal.h |    2 --
 kernel/signal.c        |   14 ++++----------
 3 files changed, 4 insertions(+), 14 deletions(-)
diff mbox series

Patch

--- a/include/linux/compat.h~x86-signal-dont-do-sas_ss_reset-until-we-are-certain-that-sigframe-wont-be-abandoned
+++ a/include/linux/compat.h
@@ -532,8 +532,6 @@  int __compat_save_altstack(compat_stack_
 			&__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);
 
 /*
--- a/include/linux/signal.h~x86-signal-dont-do-sas_ss_reset-until-we-are-certain-that-sigframe-wont-be-abandoned
+++ a/include/linux/signal.h
@@ -462,8 +462,6 @@  int __save_altstack(stack_t __user *, un
 	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
--- a/kernel/signal.c~x86-signal-dont-do-sas_ss_reset-until-we-are-certain-that-sigframe-wont-be-abandoned
+++ a/kernel/signal.c
@@ -2829,6 +2829,8 @@  static void signal_delivered(struct ksig
 	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,
 	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_
 			 &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