Commit 7d503feb authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

exec: In setup_new_exec cache current in the local variable me 



At least gcc 8.3 when generating code for x86_64 has a hard time
consolidating multiple calls to current aka get_current(), and winds
up unnecessarily rereading %gs:current_task several times in
setup_new_exec.

Caching the value of current in the local variable of me generates
slightly better and shorter assembly.

Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarGreg Ungerer <gerg@linux-m68k.org>
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent 96ecee29

fs/exec.c

+12 −11
Original line number Diff line number Diff line
@@ -1391,6 +1391,7 @@ EXPORT_SYMBOL(would_dump); 


void setup_new_exec(struct linux_binprm * bprm)

{

	struct task_struct *me = current;

	/*

	 * Once here, prepare_binrpm() will not be called any more, so

	 * the final state of setuid/setgid/fscaps can be merged into the
@@ -1400,7 +1401,7 @@ void setup_new_exec(struct linux_binprm * bprm) 


	if (bprm->secureexec) {

		/* Make sure parent cannot signal privileged process. */

		current->pdeath_signal = 0;

		me->pdeath_signal = 0;



		/*

		 * For secureexec, reset the stack limit to sane default to
@@ -1413,9 +1414,9 @@ void setup_new_exec(struct linux_binprm * bprm) 
			bprm->rlim_stack.rlim_cur = _STK_LIM;

	}



	arch_pick_mmap_layout(current->mm, &bprm->rlim_stack);

	arch_pick_mmap_layout(me->mm, &bprm->rlim_stack);



	current->sas_ss_sp = current->sas_ss_size = 0;

	me->sas_ss_sp = me->sas_ss_size = 0;



	/*

	 * Figure out dumpability. Note that this checking only of current
@@ -1431,18 +1432,18 @@ void setup_new_exec(struct linux_binprm * bprm) 


	arch_setup_new_exec();

	perf_event_exec();

	__set_task_comm(current, kbasename(bprm->filename), true);

	__set_task_comm(me, kbasename(bprm->filename), true);



	/* Set the new mm task size. We have to do that late because it may

	 * depend on TIF_32BIT which is only updated in flush_thread() on

	 * some architectures like powerpc

	 */

	current->mm->task_size = TASK_SIZE;

	me->mm->task_size = TASK_SIZE;



	/* An exec changes our domain. We are no longer part of the thread

	   group */

	WRITE_ONCE(current->self_exec_id, current->self_exec_id + 1);

	flush_signal_handlers(current, 0);

	WRITE_ONCE(me->self_exec_id, me->self_exec_id + 1);

	flush_signal_handlers(me, 0);



	/*

	 * install the new credentials for this executable
@@ -1458,16 +1459,16 @@ void setup_new_exec(struct linux_binprm * bprm) 
	 * wait until new credentials are committed

	 * by commit_creds() above

	 */

	if (get_dumpable(current->mm) != SUID_DUMP_USER)

		perf_event_exit_task(current);

	if (get_dumpable(me->mm) != SUID_DUMP_USER)

		perf_event_exit_task(me);

	/*

	 * cred_guard_mutex must be held at least to this point to prevent

	 * ptrace_attach() from altering our determination of the task's

	 * credentials; any time after this it may be unlocked.

	 */

	security_bprm_committed_creds(bprm);

	mutex_unlock(&current->signal->exec_update_mutex);

	mutex_unlock(&current->signal->cred_guard_mutex);

	mutex_unlock(&me->signal->exec_update_mutex);

	mutex_unlock(&me->signal->cred_guard_mutex);

}

EXPORT_SYMBOL(setup_new_exec);

CRA Git | Maintained and supported by SUSTech CRA and CCSE