[GSOC] capsicum week4 report (and question)

[Joris GIOVANNANGELI <joris@xxxxxxxxxxxxxxxx>]

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Hi,

this week i've been fixing the bugs I introduced at the end of last week
in the capability mode. I wrote some test programs to verify that the
comportment of the new syscalls is correct. The capability mode is
mostly done, i've been groking the kernel to see where
holdfp/holdvnode/holdsock are used and understand what capability is
needed in each case for the operation. This is not finished and i'll be
doing that the whole next week.

I also need to add a filter in the syscall path to check if the syscall
is allowed in capability mode. FreeBSD has a different sysent table than
dragonfly. They have added a a flag field for each syscall. A new flag
SYF_CAPENABLED can be set for each syscall, and the syscall path checks
if the flag is set before calling the syscall if the process is in
capability mode
(https://gitweb.dragonflybsd.org/freebsd.git/blob/HEAD:/sys/kern/subr_syscall.c#l106).
I need a mechanism to achieve a similar goal in dragonfly. I see two
possibilities :

 * Adding a flag field in the sysent like freebsd
 * If i'm correct, the sysent vector is only accessed via the p_sysent
field of the proc structure. The syscall is lookup in trac.c (machine
dependent code) using this pointer. The sysent vector could be context
dependent, with two statically alloced sysent vectors : one for normal
processes, and one for processes in capability mode. Switching a process
in capability mode would hence only have to switch the p_sysent pointer
to the other sysent vector.
 * Other suggestions welcome !

Thanks,
Joris
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