linux-kernel - Re: Chromium sandbox on LoongArch and statx -- seccomp deep argument inspection again?

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Date: Mon, 26 Feb 2024 16:40:25 +0100
From: Christian Brauner <brauner@...nel.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: Xi Ruoyao <xry111@...111.site>, Icenowy Zheng <uwu@...nowy.me>, 
	Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>, linux-api@...r.kernel.org, 
	Kees Cook <keescook@...omium.org>, Xuefeng Li <lixuefeng@...ngson.cn>, 
	Jianmin Lv <lvjianmin@...ngson.cn>, Xiaotian Wu <wuxiaotian@...ngson.cn>, 
	WANG Rui <wangrui@...ngson.cn>, Miao Wang <shankerwangmiao@...il.com>, 
	"loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>, Linux-Arch <linux-arch@...r.kernel.org>, 
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Chromium sandbox on LoongArch and statx -- seccomp deep argument
 inspection again?

On Mon, Feb 26, 2024 at 02:46:49PM +0100, Arnd Bergmann wrote:
> On Mon, Feb 26, 2024, at 14:32, Christian Brauner wrote:
> > On Mon, Feb 26, 2024 at 10:20:23AM +0100, Arnd Bergmann wrote:
> >> On Mon, Feb 26, 2024, at 08:09, Xi Ruoyao wrote:
> >
> > What this tells me without knowing the exact reason is that they thought
> > "Oh, if we just return ENOSYS then the workload or glibc will just
> > always be able to fallback to fstat() or fstatat()". Which ultimately is
> > the exact same thing that containers often assume.
> >
> > So really, just skipping on various system calls isn't going to work.
> > You can't just implement new system calls and forget about the rest
> > unless you know exactly what workloads your architecure will run on.
> >
> > Please implement fstat() or fstatat() and stop inventing hacks for
> > statx() to make weird sandboxing rules work, please.
> 
> Do you mean we should add fstat64_time64() for all architectures
> then? Would use use the same structure layout as statx for this,
> the 64-bit version of the 'struct stat' layout from
> include/uapi/asm-generic/stat.h, or something new that solves
> the same problems?
> 
> I definitely don't want to see a new time32 API added to
> mips64 and the 32-bit architectures, so the existing stat64
> interface won't work as a statx replacement.

I don't specifically care but the same way you don't want to see newer
time32 apis added to architectures I don't want to have hacks in our
system calls that aren't even a clear solution to the problem outlined
in this thread.

Short of adding fstatx() the problem isn't solved by a new flag to
statx() as explained in my other mails. But I'm probably missing
something here because I find this notion of "design system calls for
seccomp and the Chromium sandbox" to be an absurd notion and it makes me
a bit impatient.

And fwiw, once mseal() lands seccomp should be a lot easier to get deep
argument inspection.