lkml.org 
[lkml]   [2020]   [May]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Date
    Subject[PATCH 5/7] 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.

    Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
    ---
    fs/exec.c | 23 ++++++++++++-----------
    1 file changed, 12 insertions(+), 11 deletions(-)

    diff --git a/fs/exec.c b/fs/exec.c
    index 93e40f865523..8c3abafb9bb1 100644
    --- a/fs/exec.c
    +++ b/fs/exec.c
    @@ -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);

    --
    2.20.1
    \
     
     \ /
      Last update: 2020-05-05 21:48    [W:5.550 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site