signals/sigaltstack, x86/signals: Unify the x86 sigaltstack check with other architectures

Currently x86's get_sigframe() checks for "current->sas_ss_size"
to determine whether there is a need to switch to sigaltstack.
The common practice used by all other arches is to check for
sas_ss_flags(sp) == 0

This patch makes the code consistent with other architectures.

The slight complexity of the patch is added by the optimization on
!sigstack check that was requested by Andy Lutomirski: sas_ss_flags(sp)==0
already implies that we are not on a sigstack, so the code is shuffled
to avoid the duplicate checking.

This patch should have no user-visible impact.

Signed-off-by: Stas Sergeev <stsp@list.ru>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-api@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1460665206-13646-2-git-send-email-stsp@list.ru
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 11 insertions, 12 deletions

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 548ddf7d6fd2..3e84ef16f657 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -248,18 +248,17 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size,
         if (config_enabled(CONFIG_X86_64))
                 sp -= 128;
 
-        if (!onsigstack) {
-                /* This is the X/Open sanctioned signal stack switching.  */
-                if (ka->sa.sa_flags & SA_ONSTACK) {
-                        if (current->sas_ss_size)
-                                sp = current->sas_ss_sp + current->sas_ss_size;
-                } else if (config_enabled(CONFIG_X86_32) &&
-                           (regs->ss & 0xffff) != __USER_DS &&
-                           !(ka->sa.sa_flags & SA_RESTORER) &&
-                           ka->sa.sa_restorer) {
-                                /* This is the legacy signal stack switching. */
-                                sp = (unsigned long) ka->sa.sa_restorer;
-                }
+        /* This is the X/Open sanctioned signal stack switching.  */
+        if (ka->sa.sa_flags & SA_ONSTACK) {
+                if (sas_ss_flags(sp) == 0)
+                        sp = current->sas_ss_sp + current->sas_ss_size;
+        } else if (config_enabled(CONFIG_X86_32) &&
+                   !onsigstack &&
+                   (regs->ss & 0xffff) != __USER_DS &&
+                   !(ka->sa.sa_flags & SA_RESTORER) &&
+                   ka->sa.sa_restorer) {
+                /* This is the legacy signal stack switching. */
+                sp = (unsigned long) ka->sa.sa_restorer;
         }
 
         if (fpu->fpstate_active) {