Re: [RFC] x86: restrict pid namespaces to 32 or 64 bit syscalls

From: H. Peter Anvin
Date: Mon Aug 15 2011 - 15:00:39 EST

On 08/15/2011 11:51 AM, Solar Designer wrote:
> I agree with you that i386 vs x86-64 vs x32 is one axis and syscall
> number is another axis.


> Per-syscall restrictions are also useful, but primarily at a different
> level - I'd expect them to be used in specific programs, such as Chrome
> and vsftpd. Those programs may also want to limit themselves to a
> certain type of syscalls (that is, on the i386 vs x86-64 vs x32 axis),
> thereby making use of both features at once. Or they might even have to
> do that, depending on how we implement the syscall restrictions.
> Per your suggestion, if I understand correctly, any task that wants to
> restrict itself on the i386 vs x86-64 vs x32 axis will have TIF_SECCOMP
> set and will incur calls into __secure_computing(). This is unnecessary
> overhead for the case when we have a restriction over this axis only,
> without per-syscall restrictions. Vasiliy's patch avoids such overhead.

There is really no bloody difference between i386 vs x86-64 and, say,
sys_oldstat versus sys_stat, or anything else along those lines.
Putting in a bunch of ad hoc facilities because of semi-plausible
performance wins rather than building a sane filtering facility which
can be optimized as a single path is ridiculous.

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