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x86, smap: Reduce the SMAP overhead for signal handling

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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
This commit is contained in:
H. Peter Anvin
2012-09-21 12:43:15 -07:00
parent 40d3cd6695
commit 5e88353d8b
3 changed files with 27 additions and 23 deletions
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24
arch/x86/kernel/signal.c
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@@ -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;