linux-kernel - Re: [PATCH] LoongArch: Define __ARCH_WANT_NEW

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Date: Sat, 11 May 2024 22:28:37 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: Huacai Chen <chenhuacai@...ngson.cn>, loongarch@...ts.linux.dev, 
	Linux-Arch <linux-arch@...r.kernel.org>, Xuefeng Li <lixuefeng@...ngson.cn>, 
	guoren <guoren@...nel.org>, WANG Xuerui <kernel@...0n.name>, 
	Jiaxun Yang <jiaxun.yang@...goat.com>, linux-kernel@...r.kernel.org, 
	loongson-kernel@...ts.loongnix.cn, stable@...r.kernel.org
Subject: Re: [PATCH] LoongArch: Define __ARCH_WANT_NEW_STAT in unistd.h

Hi, Arnd,

On Sat, May 11, 2024 at 8:17 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Sat, May 11, 2024, at 12:01, Huacai Chen wrote:
> > Chromium sandbox apparently wants to deny statx [1] so it could properly
> > inspect arguments after the sandboxed process later falls back to fstat.
> > Because there's currently not a "fd-only" version of statx, so that the
> > sandbox has no way to ensure the path argument is empty without being
> > able to peek into the sandboxed process's memory. For architectures able
> > to do newfstatat though, glibc falls back to newfstatat after getting
> > -ENOSYS for statx, then the respective SIGSYS handler [2] takes care of
> > inspecting the path argument, transforming allowed newfstatat's into
> > fstat instead which is allowed and has the same type of return value.
> >
> > But, as LoongArch is the first architecture to not have fstat nor
> > newfstatat, the LoongArch glibc does not attempt falling back at all
> > when it gets -ENOSYS for statx -- and you see the problem there!
>
> My main objection here is that this is inconsistent with 32-bit
> architectures: we normally have newfstatat() on 64-bit
> architectures but fstatat64() on 32-bit ones. While loongarch64
> is the first 64-bit one that is missing newfstatat(), we have
> riscv32 already without fstatat64().
Then how to move forward? Xuerui said that he wants to improve
seccomp, but a long time has already passed. And I think we should
solve this problem before Debian loong64 ports become usable.

>
> Importantly, we can't just add fstatat64() on riscv32 because
> there is no time64 version for it other than statx(), and I don't
> want the architectures to diverge more than necessary.
> I would not mind adding a variant of statx() that works for
> both riscv32 and loongarch64 though, if it gets added to all
> architectures.
As far as I know, Ren Guo is trying to implement riscv64 kernel +
riscv32 userspace, so I think riscv32 kernel won't be widely used?

Huacai
>
>       Arnd
>