On Mon, Feb 1, 2021 at 9:34 PM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > On Thu, Jan 28, 2021 at 11:08 PM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > > > On Thu, Jan 28, 2021 at 11:51 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > > > > > On Tue, Jan 26, 2021 at 5:52 AM 'Michal Hocko' via kernel-team > > > <kernel-team@xxxxxxxxxxx> wrote: > > > > > > > > On Wed 20-01-21 14:17:39, Jann Horn wrote: > > > > > On Wed, Jan 13, 2021 at 3:22 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > > > On Tue 12-01-21 09:51:24, Suren Baghdasaryan wrote: > > > > > > > On Tue, Jan 12, 2021 at 9:45 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > On 01/12, Michal Hocko wrote: > > > > > > > > > > > > > > > > > > On Mon 11-01-21 09:06:22, Suren Baghdasaryan wrote: > > > > > > > > > > > > > > > > > > > What we want is the ability for one process to influence another process > > > > > > > > > > in order to optimize performance across the entire system while leaving > > > > > > > > > > the security boundary intact. > > > > > > > > > > Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ > > > > > > > > > > and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata > > > > > > > > > > and CAP_SYS_NICE for influencing process performance. > > > > > > > > > > > > > > > > > > I have to say that ptrace modes are rather obscure to me. So I cannot > > > > > > > > > really judge whether MODE_READ is sufficient. My understanding has > > > > > > > > > always been that this is requred to RO access to the address space. But > > > > > > > > > this operation clearly has a visible side effect. Do we have any actual > > > > > > > > > documentation for the existing modes? > > > > > > > > > > > > > > > > > > I would be really curious to hear from Jann and Oleg (now Cced). > > > > > > > > > > > > > > > > Can't comment, sorry. I never understood these security checks and never tried. > > > > > > > > IIUC only selinux/etc can treat ATTACH/READ differently and I have no idea what > > > > > > > > is the difference. > > > > > > > > > > Yama in particular only does its checks on ATTACH and ignores READ, > > > > > that's the difference you're probably most likely to encounter on a > > > > > normal desktop system, since some distros turn Yama on by default. > > > > > Basically the idea there is that running "gdb -p $pid" or "strace -p > > > > > $pid" as a normal user will usually fail, but reading /proc/$pid/maps > > > > > still works; so you can see things like detailed memory usage > > > > > information and such, but you're not supposed to be able to directly > > > > > peek into a running SSH client and inject data into the existing SSH > > > > > connection, or steal the cryptographic keys for the current > > > > > connection, or something like that. > > > > > > > > > > > > I haven't seen a written explanation on ptrace modes but when I > > > > > > > consulted Jann his explanation was: > > > > > > > > > > > > > > PTRACE_MODE_READ means you can inspect metadata about processes with > > > > > > > the specified domain, across UID boundaries. > > > > > > > PTRACE_MODE_ATTACH means you can fully impersonate processes with the > > > > > > > specified domain, across UID boundaries. > > > > > > > > > > > > Maybe this would be a good start to document expectations. Some more > > > > > > practical examples where the difference is visible would be great as > > > > > > well. > > > > > > > > > > Before documenting the behavior, it would be a good idea to figure out > > > > > what to do with perf_event_open(). That one's weird in that it only > > > > > requires PTRACE_MODE_READ, but actually allows you to sample stuff > > > > > like userspace stack and register contents (if perf_event_paranoid is > > > > > 1 or 2). Maybe for SELinux things (and maybe also for Yama), there > > > > > should be a level in between that allows fully inspecting the process > > > > > (for purposes like profiling) but without the ability to corrupt its > > > > > memory or registers or things like that. Or maybe perf_event_open() > > > > > should just use the ATTACH mode. > > > > > > > > Thanks for the clarification. I still cannot say I would have a good > > > > mental picture. Having something in Documentation/core-api/ sounds > > > > really needed. Wrt to perf_event_open it sounds really odd it can do > > > > more than other places restrict indeed. Something for the respective > > > > maintainer but I strongly suspect people simply copy the pattern from > > > > other places because the expected semantic is not really clear. > > > > > > > > > > Sorry, back to the matters of this patch. Are there any actionable > > > items for me to take care of before it can be accepted? The only > > > request from Andrew to write a man page is being worked on at > > > https://lore.kernel.org/linux-mm/20210120202337.1481402-1-surenb@xxxxxxxxxx/ > > > and I'll follow up with the next version. I also CC'ed stable@ for > > > this to be included into 5.10 per Andrew's request. That CC was lost > > > at some point, so CC'ing again. > > > > > > I do not see anything else on this patch to fix. Please chime in if > > > there are any more concerns, otherwise I would ask Andrew to take it > > > into mm-tree and stable@ to apply it to 5.10. > > > Thanks! > > > > process_madvise man page V2 is posted at: > > https://lore.kernel.org/linux-mm/20210129070340.566340-1-surenb@xxxxxxxxxx/ > > process_madvise man page V3 is posted at: > https://lore.kernel.org/linux-mm/20210202053046.1653012-1-surenb@xxxxxxxxxx/ > Hi Andrew, A friendly reminder to please include this patch into mm tree. There seem to be no more questions or objections. The man page you requested is accepted here: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f458bad476a3358e3a45023789cb7bb9f993 stable is CC'ed and this patch should go into 5.10 and later kernels The patch has been: Acked-by: Minchan Kim <minchan@xxxxxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> If you want me to resend it, please let me know. Thanks, Suren. > > > > > > > > > > > > -- > > > > Michal Hocko > > > > SUSE Labs > > > > > > > > -- > > > > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@xxxxxxxxxxx. > > > >
