On Wed, Feb 17, 2016 at 12:18 PM, Andrew Morton <a...@linux-foundation.org> wrote: > 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!
Other uses may be using a combination PTRACE_MODE_ATTACH|PTRACE_MODE_FSCREDS. >> > 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. Ok. Reworking the patch to use that as well. Andrew: I saw you added these to -mm already. Would you prefer a fixup patch ontop, or should I just send out a folded down v3 of the patchset? thanks -john
