linux-kernel - Re: [PATCH] x86/retpoline/entry: Disable the entire SYSCALL64 fast path with retpolines on

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Message-ID: <CA+55aFydRUyNWz5M2nWWMsLk5dW5JjRRNcFjP62yecAJ_bSDpQ@mail.gmail.com>
Date:   Fri, 26 Jan 2018 10:13:38 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Andy Lutomirski <luto@...nel.org>, Alan Cox <alan@...ux.intel.com>,
        David Laight <David.Laight@...lab.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jann Horn <jannh@...gle.com>,
        Samuel Neves <samuel.c.p.neves@...il.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86/retpoline/entry: Disable the entire SYSCALL64 fast
 path with retpolines on

On Fri, Jan 26, 2018 at 10:07 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> Umm...  What about other architectures?  Or do you want SYSCALL_DEFINE...
> to be per-arch?  I wonder how much would that "go through pt_regs" hurt
> on something like sparc...

No, but I just talked to Will Deacon about register clearing on entry,
and so I suspect that arm64 might want something similar too.

So I think some opt-in for letting architectures add their own
function would be good. Because it wouldn't be all architectures, but
it probably _would_ be more than just x86.

You need to add architecture-specific "load argX from ptregs" macros anyway.

             Linus