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Message-ID: <bf8a6390-97a6-1ab6-90ef-6399437ed38c@intel.com>
Date: Wed, 14 Aug 2019 09:48:08 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Yu-cheng Yu <yu-cheng.yu@...el.com>,
Andy Lutomirski <luto@...nel.org>
Cc: X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>,
linux-arch <linux-arch@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>,
Arnd Bergmann <arnd@...db.de>,
Balbir Singh <bsingharora@...il.com>,
Borislav Petkov <bp@...en8.de>,
Cyrill Gorcunov <gorcunov@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Eugene Syromiatnikov <esyr@...hat.com>,
Florian Weimer <fweimer@...hat.com>,
"H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>,
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Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
Peter Zijlstra <peterz@...radead.org>,
Randy Dunlap <rdunlap@...radead.org>,
"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
Dave Martin <Dave.Martin@....com>
Subject: Re: [PATCH v8 15/27] mm: Handle shadow stack page fault
On 8/14/19 9:27 AM, Yu-cheng Yu wrote:
> On Tue, 2019-08-13 at 15:55 -0700, Andy Lutomirski wrote:
>> On Tue, Aug 13, 2019 at 2:02 PM Yu-cheng Yu <yu-cheng.yu@...el.com> wrote:
>>> When a task does fork(), its shadow stack (SHSTK) must be duplicated
>>> for the child. This patch implements a flow similar to copy-on-write
>>> of an anonymous page, but for SHSTK.
>>>
>>> A SHSTK PTE must be RO and dirty. This dirty bit requirement is used
>>> to effect the copying. In copy_one_pte(), clear the dirty bit from a
>>> SHSTK PTE to cause a page fault upon the next SHSTK access. At that
>>> time, fix the PTE and copy/re-use the page.
>> Is using VM_SHSTK and special-casing all of this really better than
>> using a special mapping or other pseudo-file-backed VMA and putting
>> all the magic in the vm_operations?
> A special mapping is cleaner. However, we also need to exclude normal [RO +
> dirty] pages from shadow stack.
I don't understand what you are saying.
Are you saying that we need this VM_SHSTK flag in order to exclude
RO+HW-Dirty pages from being created in non-shadow-stack VMAs?
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