From: David Laight <David.Laight@ACULAB.COM>
To: "'Yu, Yu-cheng'" <yu-cheng.yu@intel.com>, Borislav Petkov <bp@alien8.de>
Cc: "x86@kernel.org" <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
Arnd Bergmann <arnd@arndb.de>, Andy Lutomirski <luto@kernel.org>,
Balbir Singh <bsingharora@gmail.com>,
Cyrill Gorcunov <gorcunov@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
"Eugene Syromiatnikov" <esyr@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Nadav Amit <nadav.amit@gmail.com>,
Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
Peter Zijlstra <peterz@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
Dave Martin <Dave.Martin@arm.com>,
"Weijiang Yang" <weijiang.yang@intel.com>,
Pengfei Xu <pengfei.xu@intel.com>
Subject: RE: [PATCH v17 08/26] x86/mm: Introduce _PAGE_COW
Date: Thu, 21 Jan 2021 22:16:08 +0000 [thread overview]
Message-ID: <cd9d04ab66d144b7942b5030d9813115@AcuMS.aculab.com> (raw)
In-Reply-To: <b4d4bec7-504e-2443-4cf3-0801b179000f@intel.com>
From: Yu, Yu-cheng
>
> On 1/21/2021 10:44 AM, Borislav Petkov wrote:
> > On Tue, Dec 29, 2020 at 01:30:35PM -0800, Yu-cheng Yu wrote:
> [...]
> >> @@ -343,6 +349,16 @@ static inline pte_t pte_mkold(pte_t pte)
> >>
> >> static inline pte_t pte_wrprotect(pte_t pte)
> >> {
> >> + /*
> >> + * Blindly clearing _PAGE_RW might accidentally create
> >> + * a shadow stack PTE (RW=0, Dirty=1). Move the hardware
> >> + * dirty value to the software bit.
> >> + */
> >> + if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
> >> + pte.pte |= (pte.pte & _PAGE_DIRTY) >> _PAGE_BIT_DIRTY << _PAGE_BIT_COW;
> >
> > Why the unreadable shifting when you can simply do:
> >
> > if (pte.pte & _PAGE_DIRTY)
> > pte.pte |= _PAGE_COW;
> >
> > ?
>
> It clears _PAGE_DIRTY and sets _PAGE_COW. That is,
>
> if (pte.pte & _PAGE_DIRTY) {
> pte.pte &= ~_PAGE_DIRTY;
> pte.pte |= _PAGE_COW;
> }
>
> So, shifting makes resulting code more efficient.
Does the compiler manage to do one shift?
How can it clear anything?
There is only an |= against the target.
Something horrid with ^= might set and clear.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-01-21 22:16 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-29 21:30 [PATCH v17 00/26] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 01/26] Documentation/x86: Add CET description Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 02/26] x86/cet/shstk: Add Kconfig option for user-mode control-flow protection Yu-cheng Yu
2021-01-19 11:06 ` Borislav Petkov
2021-01-19 18:10 ` Yu, Yu-cheng
2020-12-29 21:30 ` [PATCH v17 03/26] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 04/26] x86/cpufeatures: Introduce X86_FEATURE_CET and setup functions Yu-cheng Yu
2021-01-11 17:56 ` Borislav Petkov
2021-01-11 20:25 ` Yu, Yu-cheng
2021-01-11 23:09 ` Yu-cheng Yu
2021-01-12 0:09 ` Yu, Yu-cheng
2021-01-12 12:38 ` Borislav Petkov
2021-01-12 23:02 ` Yu, Yu-cheng
2021-01-13 10:04 ` Borislav Petkov
2020-12-29 21:30 ` [PATCH v17 05/26] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 06/26] x86/cet: Add control-protection fault handler Yu-cheng Yu
2021-01-19 12:04 ` Borislav Petkov
2021-01-19 19:36 ` Yu, Yu-cheng
2020-12-29 21:30 ` [PATCH v17 07/26] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 08/26] x86/mm: Introduce _PAGE_COW Yu-cheng Yu
2021-01-21 18:44 ` Borislav Petkov
2021-01-21 20:16 ` Yu, Yu-cheng
2021-01-21 20:20 ` Dave Hansen
2021-01-21 20:26 ` Dave Hansen
2021-01-21 20:44 ` Yu, Yu-cheng
2021-01-21 20:41 ` Borislav Petkov
2021-01-21 21:40 ` Yu, Yu-cheng
2021-01-21 22:16 ` David Laight [this message]
2021-01-21 22:19 ` Randy Dunlap
2021-01-21 22:32 ` David Laight
2021-01-22 21:54 ` Yu, Yu-cheng
2020-12-29 21:30 ` [PATCH v17 09/26] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 10/26] x86/mm: Update pte_modify for _PAGE_COW Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 11/26] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW Yu-cheng Yu
2021-01-25 18:27 ` Borislav Petkov
2021-01-25 21:27 ` Yu, Yu-cheng
2021-01-25 21:55 ` Borislav Petkov
2021-01-25 22:18 ` Yu, Yu-cheng
2021-01-26 10:24 ` Borislav Petkov
2021-01-26 16:45 ` Yu, Yu-cheng
2021-01-26 8:46 ` Peter Zijlstra
2021-01-26 9:40 ` Peter Zijlstra
2021-01-26 16:43 ` Yu, Yu-cheng
2020-12-29 21:30 ` [PATCH v17 12/26] mm: Introduce VM_SHSTK for shadow stack memory Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 13/26] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 14/26] x86/mm: Update maybe_mkwrite() for shadow stack Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 15/26] mm: Fixup places that call pte_mkwrite() directly Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 16/26] mm: Add guard pages around a shadow stack Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 17/26] mm/mmap: Add shadow stack pages to memory accounting Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 18/26] mm: Update can_follow_write_pte() for shadow stack Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 19/26] mm: Re-introduce vm_flags to do_mmap() Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 20/26] x86/cet/shstk: User-mode shadow stack support Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 21/26] x86/cet/shstk: Handle signals for shadow stack Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 22/26] binfmt_elf: Define GNU_PROPERTY_X86_FEATURE_1_AND properties Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 23/26] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 24/26] x86/cet/shstk: Handle thread shadow stack Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 25/26] x86/cet/shstk: Add arch_prctl functions for " Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 26/26] mm: Introduce PROT_SHSTK " Yu-cheng Yu
2021-01-04 20:08 ` [PATCH v17 00/26] Control-flow Enforcement: Shadow Stack Yu, Yu-cheng
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=cd9d04ab66d144b7942b5030d9813115@AcuMS.aculab.com \
--to=david.laight@aculab.com \
--cc=Dave.Martin@arm.com \
--cc=arnd@arndb.de \
--cc=bp@alien8.de \
--cc=bsingharora@gmail.com \
--cc=corbet@lwn.net \
--cc=dave.hansen@linux.intel.com \
--cc=esyr@redhat.com \
--cc=fweimer@redhat.com \
--cc=gorcunov@gmail.com \
--cc=hjl.tools@gmail.com \
--cc=hpa@zytor.com \
--cc=jannh@google.com \
--cc=keescook@chromium.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=luto@kernel.org \
--cc=mike.kravetz@oracle.com \
--cc=mingo@redhat.com \
--cc=nadav.amit@gmail.com \
--cc=oleg@redhat.com \
--cc=pavel@ucw.cz \
--cc=pengfei.xu@intel.com \
--cc=peterz@infradead.org \
--cc=ravi.v.shankar@intel.com \
--cc=rdunlap@infradead.org \
--cc=tglx@linutronix.de \
--cc=vedvyas.shanbhogue@intel.com \
--cc=weijiang.yang@intel.com \
--cc=x86@kernel.org \
--cc=yu-cheng.yu@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).