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Date: Wed, 17 Jan 2018 11:16:50 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Dan Williams <dan.j.williams@...el.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org,
Andi Kleen <ak@...ux.intel.com>, Kees Cook <keescook@...omium.org>,
kernel-hardening@...ts.openwall.com,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "the arch/x86 maintainers" <x86@...nel.org>,
Ingo Molnar <mingo@...hat.com>, Al Viro <viro@...iv.linux.org.uk>,
"H. Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>,
Andrew Morton <akpm@...ux-foundation.org>, Alan Cox <alan@...ux.intel.com>
Subject: Re: [PATCH v3 8/9] x86: use __uaccess_begin_nospec and ASM_IFENCE in
get_user paths
On Tue, Jan 16, 2018 at 8:30 PM, Dan Williams <dan.j.williams@...el.com> wrote:
>
> I think the access_ok() conversion to return a speculation sanitized
> pointer or NULL is the way to go unless I'm missing something simpler.
No, that's way too big of a conversion.
Just make get_user() and friends (that currently use ASM_STAC) use the
address masking.
The people who use uaccess_begin() can use the lfence there.
Basically, the rule is trivial: find all 'stac' users, and use address
masking if those users already integrate the limit check, and lfence
they don't.
Linus
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