I'm implementing the memory protection key interfaces for glibc and
noticed that the pkey_alloc manpage in particular is a bit removed from
reality.
Here's what I found:
The flags argument is reserved and currently must be zero.
The access_rights argument instructs the kernel to set the access rights
for the new key for the current thread only (!). It's a bitmask with
bits PKEY_DISABLE_ACCESS and PKEY_DISABLE_WRITE.
So in essence, both arguments are not needed right now because the
access rights of the current thread for the new key could easily be
changed in user space.
To repeat, pkey_alloc affects the access rights of the current thread.
Other threads retain their existing access rights. The default rights
for the process apparently can be set with the init_pkru parameter on
recent kernels (I have not tried that).
The manpage mentions only the key leak related to pkey_mprotect
(pkey_free while a page still is still associated with that key). There
is another one which affects a pkey_alloc/pthread_create/pkey_free
sequence, where any created threads retain their access rights. I
raised this issue of key reuse in a recent thread (MPK: pkey_free and
key reuse), so perhaps there will be a way
Anyway, the important manpage fix for now would be to fix the
description of the flags and access_rights parameters.
Thanks,
Florian
--
To unsubscribe from this list: send the line "unsubscribe linux-man" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
