Commit 5e88353d authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

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: default avatarH. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1348256595-29119-12-git-send-email-hpa@linux.intel.com
parent 40d3cd66

arch/x86/ia32/ia32_signal.c

+7 −5
Original line number Diff line number Diff line
@@ -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;

arch/x86/include/asm/uaccess.h

+6 −8
Original line number Diff line number Diff line
@@ -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)



/**

arch/x86/kernel/signal.c

+14 −10
Original line number Diff line number Diff line
@@ -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;

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