[PATCH 3/4] x86: signal: unify the sigaltstack check with other arches

[Stas Sergeev]

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 arches and also
allows for the further sigaltstack improvements within this patch serie.

CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
CC: linux-kernel@xxxxxxxxxxxxxxx
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
CC: x86@xxxxxxxxxx
CC: Borislav Petkov <bp@xxxxxxx>
CC: Brian Gerst <brgerst@xxxxxxxxx>
CC: Oleg Nesterov <oleg@xxxxxxxxxx>
CC: Richard Weinberger <richard@xxxxxx>

Signed-off-by: Stas Sergeev <stsp@xxxxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kernel/signal.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index cb6282c..3955259 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -216,7 +216,7 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs 
*regs, size_t frame_size,
     if (!onsigstack) {
         /* This is the X/Open sanctioned signal stack switching. */
         if (ka->sa.sa_flags & SA_ONSTACK) {
-            if (current->sas_ss_size)
+            if (sas_ss_flags(sp) == 0)
                 sp = current->sas_ss_sp + current->sas_ss_size;
         } else if (config_enabled(CONFIG_X86_32) &&
                (regs->ss & 0xffff) != __USER_DS &&
--
2.5.0