On Tue, Dec 08, 2020 at 10:07:17AM -0800, Andy Lutomirski wrote: > On Thu, Nov 19, 2020 at 10:05 AM Topi Miettinen <toiwoton@xxxxxxxxx> wrote: > > > > On 19.11.2020 18.32, Zbigniew Jędrzejewski-Szmek wrote: > > > On Thu, Nov 19, 2020 at 08:17:08AM -0800, Andy Lutomirski wrote: > > >> Hi udev people- > > >> > > >> The upcoming Linux SGX driver has a device node /dev/sgx. User code > > >> opens it, does various setup things, mmaps it, and needs to be able to > > >> create PROT_EXEC mappings. This gets quite awkward if /dev is mounted > > >> noexec. > > >> > > >> Can udev arrange to make a device node executable on distros that make > > >> /dev noexec? This could be done by bind-mounting from an exec tmpfs. > > >> Alternatively, the kernel could probably learn to ignore noexec on > > >> /dev/sgx, but that seems a little bit evil. > > > > > > I'd be inclined to simply drop noexec from /dev by default. > > > We don't do noexec on either /tmp or /dev/shm (because that causes immediate > > > problems with stuff like Java and cffi). And if you have those two at your > > > disposal anyway, having noexec on /dev doesn't seem important. > > > > I'd propose to not enable exec globally, but if a service needs SGX, it > > could use something like MountOptions=/dev:exec only in those cases > > where it's needed. That way it's possible to disallow writable and > > executable file systems for most services (which typically don't need > > /tmp or /dev/shm either). Of course the opposite > > (MountOptions=/dev:noexec) would be also possible, but I'd expect that > > this would be needed to be used more often. > > > > I imagine the opposite would be more sensible. It seems odd to me > that we would want any SGX-using service to require both special mount > options and regular ACL permissions. > > As a further argument, I just did this on a Fedora system: > > $ find /dev -perm /ugo+x -a \! -type d -a \! -type l > > No results. So making /dev noexec doesn't seem to have any benefit. Neither does my Ubuntu installation with '-xdev' added (because of /dev/shm mount). find /dev -xdev -perm /ugo+x -a \! -type d -a \! -type l /Jarkko
