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From: "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
To: Dave Hansen <dave.hansen@intel.com>,
	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-doc@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	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>,
	"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>,
	Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v18 05/25] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states
Date: Mon, 1 Feb 2021 15:14:20 -0800	[thread overview]
Message-ID: <ea573956-a739-aef6-6073-3216eb3158c6@intel.com> (raw)
In-Reply-To: <834ac0ae-b03c-dfa0-3e91-72587226613f@intel.com>

On 2/1/2021 3:12 PM, Dave Hansen wrote:
> On 2/1/21 3:05 PM, Yu, Yu-cheng wrote:
>>>>
>>>
>>> Wait a sec...  What about *THIS* series?  Will *THIS* series give us
>>> oopses when userspace blasts a new XSAVE buffer in with NT_X86_XSTATE?
>>>
>>
>> Fortunately, CET states are supervisor states.  NT_x86_XSTATE has only
>> user states.
> 
> Ahhh, good point.  You did mention this in the changelog:
> 
>> Control-flow Enforcement Technology (CET) introduces these MSRs:
>>
>>      MSR_IA32_U_CET (user-mode CET settings),
>>      MSR_IA32_PL3_SSP (user-mode shadow stack pointer),
>>
>>      MSR_IA32_PL0_SSP (kernel-mode shadow stack pointer),
>>      MSR_IA32_PL1_SSP (Privilege Level 1 shadow stack pointer),
>>      MSR_IA32_PL2_SSP (Privilege Level 2 shadow stack pointer),
>>      MSR_IA32_S_CET (kernel-mode CET settings),
>>      MSR_IA32_INT_SSP_TAB (exception shadow stack table).
>>
>> The two user-mode MSRs belong to XFEATURE_CET_USER.  The first three of
>> kernel-mode MSRs belong to XFEATURE_CET_KERNEL.  Both XSAVES states are
>> supervisor states.
> 
> This is another great place to add some information about the feature.
> 
> "Both XSAVES states are supervisor states." ...  This means that there
> is no direct, unprivileged access to this state, making it harder for an
> attacker to subvert CET.
> 
> You could also allude to the future ptrace() support here.
> 

I will add that.

  reply	other threads:[~2021-02-01 23:15 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-27 21:24 [PATCH v18 00/25] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 01/25] Documentation/x86: Add CET description Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 02/25] x86/cet/shstk: Add Kconfig option for user-mode control-flow protection Yu-cheng Yu
2021-01-29 19:42   ` Dave Hansen
2021-01-29 19:58     ` Andy Lutomirski
2021-01-29 20:33       ` Dave Hansen
2021-01-29 20:46         ` Borislav Petkov
2021-01-29 21:13           ` Yu, Yu-cheng
2021-01-29 20:00     ` Yu, Yu-cheng
2021-01-27 21:25 ` [PATCH v18 03/25] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 04/25] x86/cpufeatures: Introduce X86_FEATURE_CET and setup functions Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 05/25] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Yu-cheng Yu
2021-01-29 21:00   ` [NEEDS-REVIEW] " Dave Hansen
2021-01-29 22:35     ` Yu, Yu-cheng
2021-01-29 22:53       ` Dave Hansen
2021-02-01 22:43         ` Yu, Yu-cheng
2021-02-01 22:59           ` Dave Hansen
2021-02-01 23:05             ` Yu, Yu-cheng
2021-02-01 23:12               ` Dave Hansen
2021-02-01 23:14                 ` Yu, Yu-cheng [this message]
2021-01-27 21:25 ` [PATCH v18 06/25] x86/cet: Add control-protection fault handler Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 07/25] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 08/25] x86/mm: Introduce _PAGE_COW Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 09/25] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 10/25] x86/mm: Update pte_modify for _PAGE_COW Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 11/25] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 12/25] mm: Introduce VM_SHSTK for shadow stack memory Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 13/25] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 14/25] x86/mm: Update maybe_mkwrite() for shadow stack Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 15/25] mm: Fixup places that call pte_mkwrite() directly Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 16/25] mm: Add guard pages around a shadow stack Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 17/25] mm/mmap: Add shadow stack pages to memory accounting Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 18/25] mm: Update can_follow_write_pte() for shadow stack Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 19/25] mm: Re-introduce vm_flags to do_mmap() Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 20/25] x86/cet/shstk: User-mode shadow stack support Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 21/25] x86/cet/shstk: Handle signals for shadow stack Yu-cheng Yu
2021-02-01 22:53   ` Dave Hansen
2021-02-01 22:58     ` Yu, Yu-cheng
2021-01-27 21:25 ` [PATCH v18 22/25] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 23/25] x86/cet/shstk: Handle thread shadow stack Yu-cheng Yu
2021-01-27 21:25 ` [PATCH v18 24/25] x86/cet/shstk: Add arch_prctl functions for " Yu-cheng Yu
2021-01-29 17:07   ` Dave Hansen
2021-01-29 18:56     ` Yu, Yu-cheng
2021-01-29 19:15       ` Dave Hansen
2021-01-29 19:53         ` Yu, Yu-cheng
2021-02-03 21:54       ` Yu, Yu-cheng
2021-02-03 22:11         ` Dave Hansen
2021-02-03 22:28           ` Yu, Yu-cheng
2021-01-27 21:25 ` [PATCH v18 25/25] mm: Introduce PROT_SHSTK " Yu-cheng Yu

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