x86, smap: Reduce the SMAP overhead for signal handling

Signal handling contains a bunch of accesses to individual user space
items, which causes an excessive number of STAC and CLAC
instructions.  Instead, let get/put_user_try ... get/put_user_catch()
contain the STAC and CLAC instructions.

This means that get/put_user_try no longer nests, and furthermore that
it is no longer legal to use user space access functions other than
__get/put_user_ex() inside those blocks.  However, these macros are
x86-specific anyway and are only used in the signal-handling paths; a
simple reordering of moving the larger subroutine calls out of the
try...catch blocks resolves that problem.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1348256595-29119-12-git-send-email-hpa@linux.intel.com

1 files changed, 14 insertions, 10 deletions

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index b280908a376e..932612887e92 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -114,11 +114,12 @@ int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc,
                 regs->orig_ax = -1;             /* disable syscall checks */
 
                 get_user_ex(buf, &sc->fpstate);
-                err |= restore_i387_xstate(buf);
 
                 get_user_ex(*pax, &sc->ax);
         } get_user_catch(err);
 
+        err |= restore_i387_xstate(buf);
+
         return err;
 }
 
@@ -357,7 +358,6 @@ static int __setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                 put_user_ex(sig, &frame->sig);
                 put_user_ex(&frame->info, &frame->pinfo);
                 put_user_ex(&frame->uc, &frame->puc);
-                err |= copy_siginfo_to_user(&frame->info, info);
 
                 /* Create the ucontext.  */
                 if (cpu_has_xsave)
@@ -369,9 +369,6 @@ static int __setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                 put_user_ex(sas_ss_flags(regs->sp),
                             &frame->uc.uc_stack.ss_flags);
                 put_user_ex(current->sas_ss_size, &frame->uc.uc_stack.ss_size);
-                err |= setup_sigcontext(&frame->uc.uc_mcontext, fpstate,
-                                        regs, set->sig[0]);
-                err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
 
                 /* Set up to return from userspace.  */
                 restorer = VDSO32_SYMBOL(current->mm->context.vdso, rt_sigreturn);
@@ -389,6 +386,11 @@ static int __setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                 put_user_ex(*((u64 *)&rt_retcode), (u64 *)frame->retcode);
         } put_user_catch(err);
 
+        err |= copy_siginfo_to_user(&frame->info, info);
+        err |= setup_sigcontext(&frame->uc.uc_mcontext, fpstate,
+                                regs, set->sig[0]);
+        err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
+
         if (err)
                 return -EFAULT;
 
@@ -436,8 +438,6 @@ static int __setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                 put_user_ex(sas_ss_flags(regs->sp),
                             &frame->uc.uc_stack.ss_flags);
                 put_user_ex(me->sas_ss_size, &frame->uc.uc_stack.ss_size);
-                err |= setup_sigcontext(&frame->uc.uc_mcontext, fp, regs, set->sig[0]);
-                err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
 
                 /* Set up to return from userspace.  If provided, use a stub
                    already in userspace.  */
@@ -450,6 +450,9 @@ static int __setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                 }
         } put_user_catch(err);
 
+        err |= setup_sigcontext(&frame->uc.uc_mcontext, fp, regs, set->sig[0]);
+        err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
+
         if (err)
                 return -EFAULT;
 
@@ -855,9 +858,6 @@ static int x32_setup_rt_frame(int sig, struct k_sigaction *ka,
                             &frame->uc.uc_stack.ss_flags);
                 put_user_ex(current->sas_ss_size, &frame->uc.uc_stack.ss_size);
                 put_user_ex(0, &frame->uc.uc__pad0);
-                err |= setup_sigcontext(&frame->uc.uc_mcontext, fpstate,
-                                        regs, set->sig[0]);
-                err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
 
                 if (ka->sa.sa_flags & SA_RESTORER) {
                         restorer = ka->sa.sa_restorer;
@@ -869,6 +869,10 @@ static int x32_setup_rt_frame(int sig, struct k_sigaction *ka,
                 put_user_ex(restorer, &frame->pretcode);
         } put_user_catch(err);
 
+        err |= setup_sigcontext(&frame->uc.uc_mcontext, fpstate,
+                                regs, set->sig[0]);
+        err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
+
         if (err)
                 return -EFAULT;