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.
-Topi
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