From: Andrew Cooper <andrew.cooper3@citrix.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
Yu-cheng Yu <yu-cheng.yu@intel.com>,
the arch/x86 maintainers <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
linux-arch <linux-arch@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
"Arnd Bergmann" <arnd@arndb.de>,
Andy Lutomirski <luto@kernel.org>,
Balbir Singh <bsingharora@gmail.com>,
Borislav Petkov <bp@alien8.de>,
Cyrill Gorcunov <gorcunov@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
"Eugene Syromiatnikov" <esyr@redhat.com>,
Florian Weimer <fweimer@redhat.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>
Subject: Re: [PATCH v10 01/26] Documentation/x86: Add CET description
Date: Sat, 16 May 2020 15:09:22 +0100 [thread overview]
Message-ID: <f8ce9863-6ada-2bc4-5141-122f64292aba@citrix.com> (raw)
In-Reply-To: <CAMe9rOqwbxis1xEWbOsftMB9Roxdb3=dp=_MgK8z2pwPP36uRw@mail.gmail.com>
On 16/05/2020 03:37, H.J. Lu wrote:
> On Fri, May 15, 2020 at 5:13 PM Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>> Finally seeing as the question was asked but not answered, it is
>> actually quite easy to figure out whether shadow stacks are enabled in
>> the current thread.
>>
>> mov $1, %eax
>> rdsspd %eax
> This is for 32-bit mode.
It actually works for both, if all you need is a shstk yes/no check.
Usually, you also want SSP in the yes case, so substitute rdsspq %rax as
appropriate.
(On a tangent - binutils mandating the D/Q suffixes is very irritating
with mixed 32/64bit code because you have to #ifdef your instructions
despite the register operands being totally unambiguous. Also, D is the
wrong suffix for AT&T syntax, and should be L. Frankly - the Intel
manuals are wrong and should not have the operand size suffix included
in the opcode name, as they are consistent with all the other
instructions in this regard.)
> I use
>
> /* Check if shadow stack is in use. */
> xorl %esi, %esi
> rdsspq %rsi
> testq %rsi, %rsi
> /* Normal return if shadow stack isn't in use. */
> je L(no_shstk)
This is probably fine for user code, as I don't think it would be
legitimate for shstk to be enabled, with SSP being 0.
Sadly, the same is not true for kernel shadow stacks.
SSP is 0 after SYSCALL, SYSENTER and CLRSSBSY, and you've got to be
careful to re-establish the shadow stack before a CALL, interrupt or
exception tries pushing a word onto the shadow stack at 0xfffffffffffffff8.
It is a very good (lucky?) thing that frame is unmapped for other
reasons, because this corner case does not protect against multiple
threads/cores using the same shadow stack concurrently.
~Andrew
next prev parent reply other threads:[~2020-05-16 14:09 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-29 22:07 [PATCH v10 00/26] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 01/26] Documentation/x86: Add CET description Yu-cheng Yu
2020-04-29 22:53 ` Dave Hansen
2020-04-29 23:02 ` Yu-cheng Yu
2020-05-12 23:20 ` Yu-cheng Yu
2020-05-15 18:39 ` Dave Hansen
2020-05-15 21:33 ` Yu-cheng Yu
2020-05-15 22:43 ` Dave Hansen
2020-05-15 23:29 ` Yu-cheng Yu
2020-05-15 23:56 ` Dave Hansen
2020-05-16 2:51 ` H.J. Lu
2020-05-17 23:09 ` Dave Hansen
2020-05-16 2:53 ` Yu-cheng Yu
2020-05-18 13:41 ` Dave Hansen
2020-05-18 14:01 ` H.J. Lu
2020-05-18 14:26 ` Dave Hansen
2020-05-18 14:21 ` Yu-cheng Yu
2020-05-18 23:47 ` Yu-cheng Yu
2020-05-19 0:38 ` Dave Hansen
2020-05-19 1:35 ` Andy Lutomirski
2020-05-20 1:04 ` Andy Lutomirski
2020-05-29 2:08 ` Yu-cheng Yu
2020-05-16 0:13 ` Andrew Cooper
2020-05-16 2:37 ` H.J. Lu
2020-05-16 14:09 ` Andrew Cooper [this message]
2020-05-22 16:49 ` Peter Zijlstra
2020-05-22 17:48 ` Andrew Cooper
2020-04-29 22:07 ` [PATCH v10 02/26] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 03/26] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states Yu-cheng Yu
2020-07-23 16:10 ` Sean Christopherson
2020-07-23 16:21 ` Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 04/26] x86/cet: Add control-protection fault handler Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 05/26] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack Yu-cheng Yu
2020-05-07 15:55 ` Dave Hansen
2020-05-07 16:59 ` Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 06/26] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 07/26] x86/mm: Remove _PAGE_DIRTY_HW from kernel RO pages Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 08/26] x86/mm: Introduce _PAGE_COW Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 09/26] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 10/26] x86/mm: Update pte_modify for _PAGE_COW Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 11/26] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY_HW to _PAGE_COW Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 12/26] mm: Introduce VM_SHSTK for shadow stack memory Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 13/26] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 14/26] x86/mm: Update maybe_mkwrite() for shadow stack Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 15/26] mm: Fixup places that call pte_mkwrite() directly Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 16/26] mm: Add guard pages around a shadow stack Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 17/26] mm/mmap: Add shadow stack pages to memory accounting Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 18/26] mm: Update can_follow_write_pte() for shadow stack Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 19/26] x86/cet/shstk: User-mode shadow stack support Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 20/26] x86/cet/shstk: Handle signals for shadow stack Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 21/26] ELF: UAPI and Kconfig additions for ELF program properties Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 22/26] ELF: Add ELF program property parsing support Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 23/26] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 24/26] x86/cet/shstk: ELF header parsing for shadow stack Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 25/26] x86/cet/shstk: Handle thread " Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 26/26] x86/cet/shstk: Add arch_prctl functions for " Yu-cheng Yu
2020-05-21 22:42 ` Kees Cook
2020-05-22 17:17 ` Yu-cheng Yu
2020-05-22 17:29 ` Eugene Syromiatnikov
2020-05-22 18:13 ` Yu-cheng Yu
2020-05-21 15:15 ` [PATCH v10 00/26] Control-flow Enforcement: Shadow Stack Josh Poimboeuf
2020-05-21 15:57 ` Yu-cheng Yu
2020-05-21 18:50 ` Josh Poimboeuf
2020-05-21 19:08 ` Yu-cheng Yu
2020-07-23 16:25 ` Sean Christopherson
2020-07-23 16:41 ` Dave Hansen
2020-07-23 16:56 ` Sean Christopherson
2020-07-23 18:41 ` Dave Hansen
2020-07-24 3:40 ` Yu-cheng Yu
2020-07-24 4:50 ` Sean Christopherson
2020-07-24 4:59 ` Sean Christopherson
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