Implementing a System Call for OpenBSD

https://poolp.org/drafts/2020-05-28-015100-copy/

by soheilpro • 6 years ago

96 30 6 years ago

snvzz3• 6 years ago

Just keep in mind that adding syscalls increases the attack surface of the kernel, and complexity needs justification in general.

Linux's syscall list is out of control. The many BSDs have managed to keep it more reasonable.

saagarjha• 6 years ago

Yup, these examples are just toys but they have some issues. One is mentioned in the post itself; see if you can find more :)

twic• 6 years ago

Hey, at least Linux has now added eBPF and io_uring, both of which are ways of feeding the kernel an increasingly wide range of instructions without needing a syscall for each one!

EdSchouten3• 6 years ago

There is nothing specific about system calls that increases the attack surface. Individual sysctls, files in procfs, sysfs, ioctls, etc. are all separate attack vectors.

The last time I checked, FreeBSD's list of system calls was larger than Linux's. This is because Linux tends to expose more functionality through sysfs, procfs, ioctl, while FreeBSD uses dedicated system calls.

https://filippo.io/linux-syscall-table/ <- max = 313

https://github.com/freebsd/freebsd/blob/master/sys/kern/sysc... <- max = 576, 356 marked 'STD'

vertex-four• 6 years ago

There's an argument that files can generally just, not be visible for specific processes using the same tooling that protects other files, but none of the kernels make this particularly easy as far as I can tell.

pjmlp• 6 years ago

Have you also counted the syscalls masked as ioctls or eBPF scripts?

cyphar2• 6 years ago

That Linux table is quite a bit out-of-date -- it's at least older than Linux 3.14 (2014) based on sched_setattr's absence from the list. [1] is a much more modern table (and is updated more frequently), but it's probably simpler to just look at the actual syscall table[2]. On x86_64, there are currently 401 syscalls (syscall numbers 387 through 423 are reserved and 436 is used by a syscall not-yet-merged).

[1] https://fedora.juszkiewicz.com.pl/syscalls.html [2]: https://elixir.bootlin.com/linux/latest/source/arch/x86/entr...

panpanna• 6 years ago

Yes, but Linux also have a number of security mechanisms to limit access to syscalls (e.g. seccomp).

lewis10282823• 6 years ago

The font on that site is awful and too small. I’m on a MacBook Pro Retina 2015

anthk• 6 years ago

Use the reader mode in your browser.

zwirbl• 6 years ago

Still a weird choice of font for a website. It looks somehow ok in firefox, but unreadably thin in chromium

Enginerrrd• 6 years ago

Or just zoom in. This site works fine. It's when web developers break zoom that the sin becomes unforgiveable.

0xdeadb00f• 6 years ago

Isn't this the default LaTeX font?

lewis10282823• 6 years ago

Probably but reading something online is different to print

messe2• 6 years ago

It is, but it doesn't look good in that size on a screen. Increasing the font size would help enormously.

masklinn2• 6 years ago

Indeed the font size is way too small, both for the font and in general.

lewis10282823• 6 years ago

Yep I just changed the font size to 18px in my dev tools and it looks better. Still don't think serif fonts are the best for a blog but guess that's just my opinion.

poolpOrg• 6 years ago

Sorry, removed the article because it was a draft not meant to be published yet, I didn't think someone would spot my drafts directory... :-)

Will finish and republish in a few days.

Implementing a System Call for OpenBSD

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