Introduce [compat_]save_altstack_ex() to unbreak x86 SMAP

commit bd1c149aa9915b9abb6d83d0f01dfd2ace0680b5 upstream.

For performance reasons, when SMAP is in use, SMAP is left open for an
entire put_user_try { ... } put_user_catch(); block, however, calling
__put_user() in the middle of that block will close SMAP as the
STAC..CLAC constructs intentionally do not nest.

Furthermore, using __put_user() rather than put_user_ex() here is bad
for performance.

Thus, introduce new [compat_]save_altstack_ex() helpers that replace
__[compat_]save_altstack() for x86, being currently the only
architecture which supports put_user_try { ... } put_user_catch().

Reported-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/n/tip-es5p6y64if71k8p5u08agv9n@git.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 69562992e457..087ab2af381a 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -364,7 +364,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
                 else
                         put_user_ex(0, &frame->uc.uc_flags);
                 put_user_ex(0, &frame->uc.uc_link);
-                err |= __save_altstack(&frame->uc.uc_stack, regs->sp);
+                save_altstack_ex(&frame->uc.uc_stack, regs->sp);
 
                 /* Set up to return from userspace.  */
                 restorer = VDSO32_SYMBOL(current->mm->context.vdso, rt_sigreturn);
@@ -429,7 +429,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
                 else
                         put_user_ex(0, &frame->uc.uc_flags);
                 put_user_ex(0, &frame->uc.uc_link);
-                err |= __save_altstack(&frame->uc.uc_stack, regs->sp);
+                save_altstack_ex(&frame->uc.uc_stack, regs->sp);
 
                 /* Set up to return from userspace.  If provided, use a stub
                    already in userspace.  */
@@ -496,7 +496,7 @@ static int x32_setup_rt_frame(struct ksignal *ksig,
                 else
                         put_user_ex(0, &frame->uc.uc_flags);
                 put_user_ex(0, &frame->uc.uc_link);
-                err |= __compat_save_altstack(&frame->uc.uc_stack, regs->sp);
+                compat_save_altstack_ex(&frame->uc.uc_stack, regs->sp);
                 put_user_ex(0, &frame->uc.uc__pad0);
 
                 if (ksig->ka.sa.sa_flags & SA_RESTORER) {