On Wed, 17 Feb 2016 12:09:08 -0800 Kees Cook <keesc...@chromium.org> wrote:
> On Wed, Feb 17, 2016 at 11:35 AM, Andrew Morton > <a...@linux-foundation.org> wrote: > > On Tue, 16 Feb 2016 17:06:31 -0800 John Stultz <john.stu...@linaro.org> > > wrote: > > > >> This patch provides a proc/PID/timerslack_ns interface which > >> exposes a task's timerslack value in nanoseconds and allows it > >> to be changed. > >> > >> This allows power/performance management software to set timer > >> slack for other threads according to its policy for the thread > >> (such as when the thread is designated foreground vs. background > >> activity) > >> > >> If the value written is non-zero, slack is set to that value. > >> Otherwise sets it to the default for the thread. > >> > >> This interface checks that the calling task has permissions to > >> to use PTRACE_MODE_ATTACH_FSCREDS on the target task, so that we > >> can ensure arbitrary apps do not change the timer slack for other > >> apps. > > > > hm. What the heck is PTRACE_MODE_ATTACH_FSCREDS and why was it chosen? > > This says the writer needs to have ptrace "attach" level of access, > and that it should be checked with fscreds, as is the standard for > most /proc things like that. The only place where PTRACE_MODE_ATTACH_FSCREDS is used in all of Linux is /prc/pid/stack. Makes me curious! > > The procfs file's permissions are 0644, yes? So a process's > > timer_slack is world-readable? hm. > > This should be 600, IMO. Sounds safer.
