From: Ingo Molnar <mingo@kernel.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: tglx@linutronix.de, linux-arch@vger.kernel.org,
Tom Lendacky <thomas.lendacky@amd.com>,
Andi Kleen <ak@linux.intel.com>,
Kees Cook <keescook@chromium.org>,
kernel-hardening@lists.openwall.com, gregkh@linuxfoundation.org,
x86@kernel.org, Ingo Molnar <mingo@redhat.com>,
Al Viro <viro@zeniv.linux.org.uk>,
"H. Peter Anvin" <hpa@zytor.com>,
torvalds@linux-foundation.org, alan@linux.intel.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 04/12] x86: introduce __uaccess_begin_nospec and ifence
Date: Sun, 28 Jan 2018 10:14:37 +0100 [thread overview]
Message-ID: <20180128091437.4lbll5bev7mgdpug@gmail.com> (raw)
In-Reply-To: <151703973427.26578.15693075353773519333.stgit@dwillia2-desk3.amr.corp.intel.com>
* Dan Williams <dan.j.williams@intel.com> wrote:
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -124,6 +124,11 @@ extern int __get_user_bad(void);
>
> #define __uaccess_begin() stac()
> #define __uaccess_end() clac()
> +#define __uaccess_begin_nospec() \
> +({ \
> + stac(); \
> + ifence(); \
> +})
BTW., wouldn't it be better to switch the barrier order here, i.e. to do:
ifence(); \
stac(); \
?
The reason is that stac()/clac() is usually paired, so there's a chance with short
sequences that it would resolve with 'no externally visible changes to flags'.
Also, there's many cases where flags are modified _inside_ the STAC/CLAC section,
so grouping them together inside a speculation atom could be beneficial.
The flip side is that if the MFENCE stalls the STAC that is ahead of it could be
processed for 'free' - while it's always post barrier with my suggestion.
But in any case it would be nice to see a discussion of this aspect in the
changelog, even if the patch does not change.
Thanks,
Ingo
next prev parent reply other threads:[~2018-01-28 9:14 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-27 7:55 [PATCH v5 00/12] spectre variant1 mitigations for tip/x86/pti Dan Williams
2018-01-27 7:55 ` Dan Williams
2018-01-27 7:55 ` [PATCH v5 01/12] Documentation: document array_idx Dan Williams
2018-01-27 7:55 ` [PATCH v5 02/12] array_idx: sanitize speculative array de-references Dan Williams
2018-01-27 7:55 ` Dan Williams
2018-01-28 8:55 ` Ingo Molnar
2018-01-28 11:36 ` Thomas Gleixner
2018-01-28 11:36 ` Thomas Gleixner
2018-01-28 16:28 ` Dan Williams
2018-01-28 18:33 ` Ingo Molnar
2018-01-29 16:45 ` Dan Williams
2018-01-29 16:45 ` Dan Williams
2018-01-28 18:36 ` Thomas Gleixner
2018-01-28 18:36 ` Thomas Gleixner
2018-01-30 6:29 ` Dan Williams
2018-01-30 6:29 ` Dan Williams
2018-01-30 19:38 ` Linus Torvalds
2018-01-30 20:13 ` Dan Williams
2018-01-30 20:27 ` Van De Ven, Arjan
2018-01-31 8:03 ` Ingo Molnar
2018-01-31 14:13 ` Van De Ven, Arjan
2018-01-31 14:21 ` Greg KH
2018-01-27 7:55 ` [PATCH v5 03/12] x86: implement array_idx_mask Dan Williams
2018-01-28 9:02 ` Ingo Molnar
2018-01-27 7:55 ` [PATCH v5 04/12] x86: introduce __uaccess_begin_nospec and ifence Dan Williams
2018-01-28 9:06 ` Ingo Molnar
2018-01-28 9:14 ` Ingo Molnar [this message]
2018-01-29 20:41 ` Dan Williams
2018-01-29 20:41 ` Dan Williams
2018-01-30 6:56 ` Ingo Molnar
2018-01-27 7:55 ` [PATCH v5 05/12] x86, __get_user: use __uaccess_begin_nospec Dan Williams
2018-01-28 9:19 ` Ingo Molnar
2018-01-28 9:19 ` Ingo Molnar
2018-01-27 7:55 ` [PATCH v5 06/12] x86, get_user: use pointer masking to limit speculation Dan Williams
2018-01-27 7:55 ` Dan Williams
2018-01-28 9:25 ` Ingo Molnar
2018-01-28 9:25 ` Ingo Molnar
2018-01-27 7:55 ` [PATCH v5 07/12] x86: remove the syscall_64 fast-path Dan Williams
2018-01-28 9:29 ` Ingo Molnar
2018-01-28 9:29 ` Ingo Molnar
2018-01-28 15:22 ` Andy Lutomirski
2018-01-28 15:22 ` Andy Lutomirski
2018-01-27 7:55 ` [PATCH v5 08/12] x86: sanitize sycall table de-references under speculation Dan Williams
2018-01-28 9:36 ` Ingo Molnar
2018-01-27 7:56 ` [PATCH v5 09/12] vfs, fdtable: prevent bounds-check bypass via speculative execution Dan Williams
2018-01-27 7:56 ` [PATCH v5 10/12] kvm, x86: update spectre-v1 mitigation Dan Williams
[not found] ` <151703971300.26578.1185595719337719486.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2018-01-27 7:56 ` [PATCH v5 11/12] nl80211: sanitize array index in parse_txq_params Dan Williams
2018-01-27 7:56 ` Dan Williams
2018-01-27 7:56 ` [PATCH v5 12/12] x86/spectre: report get_user mitigation for spectre_v1 Dan Williams
2018-01-28 9:50 ` Ingo Molnar
2018-01-29 22:05 ` Dan Williams
2018-01-31 8:07 ` Ingo Molnar
2018-02-01 20:23 ` Dan Williams
2018-02-01 20:23 ` Dan Williams
2018-01-27 18:52 ` [PATCH v5 00/12] spectre variant1 mitigations for tip/x86/pti Linus Torvalds
2018-01-27 18:52 ` Linus Torvalds
2018-01-27 19:26 ` Dan Williams
2018-01-27 19:26 ` Dan Williams
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