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Message-ID: <CA+55aFwgWqNAyZ3hVYhn_s2JgdVDeyMSRKFxaU=R3jq7GRs6Bg@mail.gmail.com>
Date: Thu, 25 Jan 2018 13:53:53 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Dan Williams <dan.j.williams@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>, "the arch/x86 maintainers" <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Alan Cox <alan@...ux.intel.com>,
Jann Horn <jannh@...gle.com>, Samuel Neves <samuel.c.p.neves@...il.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 Thu, Jan 25, 2018 at 1:39 PM, Dan Williams <dan.j.williams@...el.com> wrote:
>
> If you're rejiggering, can we also put in a mechanism for detecting
> which registers to clear so that userspace can't inject useful values
> into speculation paths?
That actually becomes trivial with just the "no fastpath" patch I sent
out. You can just clear all of them.
Sure, then do_syscall_64() will reload the six first ones, but since
those are the argument registers anyway, and since they are
caller-clobbered, they have very short lifetimes. So it would
effectively not really be an issue.
But yes, SYSCALL_DEFINEx() rejiggery would close even that tiny hole.
Linus
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