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

diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 673ac9b63d6bf51ca36e2a0f18c4ca0d125d4fde..05e62a312bd9d371677dd3af2f28dee9d9e7b02d 100644 (file)
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -250,11 +250,12 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,
 
                get_user_ex(tmp, &sc->fpstate);
                buf = compat_ptr(tmp);
-               err |= restore_i387_xstate_ia32(buf);
 
                get_user_ex(*pax, &sc->ax);
        } get_user_catch(err);
 
+       err |= restore_i387_xstate_ia32(buf);
+
        return err;
 }
 
@@ -502,7 +503,6 @@ int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                put_user_ex(sig, &frame->sig);
                put_user_ex(ptr_to_compat(&frame->info), &frame->pinfo);
                put_user_ex(ptr_to_compat(&frame->uc), &frame->puc);
-               err |= copy_siginfo_to_user32(&frame->info, info);
 
                /* Create the ucontext.  */
                if (cpu_has_xsave)
@@ -514,9 +514,6 @@ int ia32_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 |= ia32_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;
@@ -532,6 +529,11 @@ int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                put_user_ex(*((u64 *)&code), (u64 *)frame->retcode);
        } put_user_catch(err);
 
+       err |= copy_siginfo_to_user32(&frame->info, info);
+       err |= ia32_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;
 

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index b92ece13c238eda0257cf6c0633031ac0294b3b5..a91acfbb1a98a7e2e6542c63ac840ff358c5e0d2 100644 (file)
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -416,9 +416,8 @@ do {                                                                        \
 } while (0)
 
 #define __get_user_asm_ex(x, addr, itype, rtype, ltype)                        \
-       asm volatile(ASM_STAC "\n"                                      \
-                    "1:        mov"itype" %1,%"rtype"0\n"              \
-                    "2: " ASM_CLAC "\n"                                \
+       asm volatile("1:        mov"itype" %1,%"rtype"0\n"              \
+                    "2:\n"                                             \
                     _ASM_EXTABLE_EX(1b, 2b)                            \
                     : ltype(x) : "m" (__m(addr)))
 
@@ -460,9 +459,8 @@ struct __large_struct { unsigned long buf[100]; };
                     : ltype(x), "m" (__m(addr)), "i" (errret), "0" (err))
 
 #define __put_user_asm_ex(x, addr, itype, rtype, ltype)                        \
-       asm volatile(ASM_STAC "\n"                                      \
-                    "1:        mov"itype" %"rtype"0,%1\n"              \
-                    "2: " ASM_CLAC "\n"                                \
+       asm volatile("1:        mov"itype" %"rtype"0,%1\n"              \
+                    "2:\n"                                             \
                     _ASM_EXTABLE_EX(1b, 2b)                            \
                     : : ltype(x), "m" (__m(addr)))
 
@@ -470,13 +468,13 @@ struct __large_struct { unsigned long buf[100]; };
  * uaccess_try and catch
  */
 #define uaccess_try    do {                                            \
-       int prev_err = current_thread_info()->uaccess_err;              \
        current_thread_info()->uaccess_err = 0;                         \
+       stac();                                                         \
        barrier();
 
 #define uaccess_catch(err)                                             \
+       clac();                                                         \
        (err) |= (current_thread_info()->uaccess_err ? -EFAULT : 0);    \
-       current_thread_info()->uaccess_err = prev_err;                  \
 } while (0)
 
 /**

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index b280908a376e20efc6773b76c6e80353ef8680f4..932612887e92ebb241e2e6e0cdcadf9695960fa6 100644 (file)
--- 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;