linux-kernel - Re: [PATCH v7 3/7] LoongArch: KVM: Add cpucfg area for kvm hypervisor

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Date: Tue, 02 Apr 2024 13:34:21 +0800
From: Xi Ruoyao <xry111@...111.site>
To: maobibo <maobibo@...ngson.cn>, WANG Xuerui <kernel@...0n.name>, Huacai
 Chen <chenhuacai@...nel.org>, Tianrui Zhao <zhaotianrui@...ngson.cn>,
 Juergen Gross <jgross@...e.com>, Paolo Bonzini <pbonzini@...hat.com>,
 Jonathan Corbet <corbet@....net>
Cc: loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	virtualization@...ts.linux.dev, kvm@...r.kernel.org
Subject: Re: [PATCH v7 3/7] LoongArch: KVM: Add cpucfg area for kvm
 hypervisor

On Tue, 2024-04-02 at 11:34 +0800, maobibo wrote:

> Are you sure that it's impossible to read some data used by the kernel
> internally?

Yes.

> There is another issue, since kernel restore T0-T7 registers and user
> space save T0-T7. Why T0-T7 is scratch registers rather than preserve
> registers like other architecture? What is the advantage if it is
> scratch registers?

I'd say "MIPS legacy."  Note that MIPS also does not preserve temp
registers, and MIPS does not have the "info leak" issue as well (or it
should have been assigned a CVE, in all these years).

I do agree maybe it's the time to move away from MIPS legacy and be more
similar to RISC-V etc now...

In Glibc we can condition __SYSCALL_CLOBBERS with #if
__LINUX_KERNEL_VERSION > xxxxxxx to take the advantage.

Huacai, Xuerui, how do you think?

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University