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From: Dave Hansen <dave.hansen@linux.intel.com>
To: Willy Tarreau <w@1wt.eu>, linux-kernel@vger.kernel.org, x86@kernel.org
Cc: Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
	Brian Gerst <brgerst@gmail.com>, Ingo Molnar <mingo@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	David Woodhouse <dwmw@amazon.co.uk>,
	Kees Cook <keescook@chromium.org>
Subject: Re: [RFC PATCH v3 6/8] x86/pti: don't mark the user PGD with _PAGE_NX.
Date: Wed, 10 Jan 2018 12:20:05 -0800	[thread overview]
Message-ID: <d81c4410-6c7f-6f99-577a-30fc92eafc6d@linux.intel.com> (raw)
In-Reply-To: <1515612500-14505-7-git-send-email-w@1wt.eu>

On 01/10/2018 11:28 AM, Willy Tarreau wrote:
> Since we're going to keep running on the same PGD when returning to
> userspace for certain performance-critical tasks, we'll need the user
> pages to be executable. So this code disables the extra protection
> that was added consisting in marking user pages _PAGE_NX so that this
> pgd remains usable for userspace.

If you are going to keep pushing this patch, or anything like it, the
least you can do is to describe the downsides.  Describe the SMEP-like
semantics that PTI gives you and describe how this shoots them in the
head for the entire process.

Also describe the reason PTI put this mechanism in place, and how this
shoots _that_ in the head for the entire process.

Granted, you have an RFC on this, but please, for the love of everything
that is good the world, please stop sending this patch set until you
have a halfway reasonable method of dealing with NX that doesn't involve
#ifdefs.  Please.

  parent reply	other threads:[~2018-01-10 20:20 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-10 19:28 [RFC PATCH v3 0/8] Per process PTI activation Willy Tarreau
2018-01-10 19:28 ` [RFC PATCH v3 1/8] x86/thread_info: add TIF_DISABLE_PTI_{NOW,NEXT} to disable PTI per task Willy Tarreau
2018-01-10 19:28 ` [RFC PATCH v3 2/8] x86/pti: add new config option PER_PROCESS_PTI Willy Tarreau
2018-01-10 19:28 ` [RFC PATCH v3 3/8] x86/pti: create the pti_adjust sysctl Willy Tarreau
2018-01-10 19:28 ` [RFC PATCH v3 4/8] x86/arch_prctl: add ARCH_DISABLE_PTI_{NOW,NEXT} to enable/disable PTI Willy Tarreau
2018-01-10 19:28 ` [RFC PATCH v3 5/8] exec: take care of disabling PTI upon execve() Willy Tarreau
2018-01-10 19:28 ` [RFC PATCH v3 6/8] x86/pti: don't mark the user PGD with _PAGE_NX Willy Tarreau
2018-01-10 19:54   ` Linus Torvalds
2018-01-10 19:59     ` Andy Lutomirski
2018-01-10 20:28       ` Woodhouse, David
2018-01-10 20:28         ` Woodhouse, David
2018-01-11  6:23         ` Willy Tarreau
2018-02-23 17:58         ` Konrad Rzeszutek Wilk
2018-02-23 19:30           ` Dave Hansen
2018-01-10 20:20   ` Dave Hansen [this message]
2018-01-11  6:27     ` Willy Tarreau
2018-01-10 19:28 ` [RFC PATCH v3 7/8] x86/entry/pti: avoid setting CR3 when it's already correct Willy Tarreau
2018-01-10 19:28 ` [RFC PATCH v3 8/8] x86/entry/pti: don't switch PGD when TIF_DISABLE_PTI_NOW is set Willy Tarreau
2018-01-10 19:35 ` [RFC PATCH v3 0/8] Per process PTI activation Linus Torvalds

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