Re: [PATCH v12 1/8] x86/cet/ibt: Add Kconfig option for user-mode Indirect Branch Tracking - Yu, Yu-cheng

From: "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
To: Pavel Machek <pavel@ucw.cz>, Randy Dunlap <rdunlap@infradead.org>
Cc: 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>,
	Peter Zijlstra <peterz@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 v12 1/8] x86/cet/ibt: Add Kconfig option for user-mode Indirect Branch Tracking
Date: Fri, 18 Sep 2020 14:25:12 -0700	[thread overview]
Message-ID: <019b5e45-b116-7f3d-f1f2-3680afbd676c@intel.com> (raw)
In-Reply-To: <20200918205933.GB4304@duo.ucw.cz>

On 9/18/2020 1:59 PM, Pavel Machek wrote:
> On Fri 2020-09-18 13:24:13, Randy Dunlap wrote:
>> Hi,
>>
>> If you do another version of this:
>>
>> On 9/18/20 12:23 PM, Yu-cheng Yu wrote:
>>> Introduce Kconfig option X86_INTEL_BRANCH_TRACKING_USER.
>>>
>>> Indirect Branch Tracking (IBT) provides protection against CALL-/JMP-
>>> oriented programming attacks.  It is active when the kernel has this
>>> feature enabled, and the processor and the application support it.
>>> When this feature is enabled, legacy non-IBT applications continue to
>>> work, but without IBT protection.
>>>
>>> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
>>> ---
>>> v10:
>>> - Change build-time CET check to config depends on.
>>>
>>>   arch/x86/Kconfig | 16 ++++++++++++++++
>>>   1 file changed, 16 insertions(+)
>>>
>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>>> index 6b6dad011763..b047e0a8d1c2 100644
>>> --- a/arch/x86/Kconfig
>>> +++ b/arch/x86/Kconfig
>>> @@ -1963,6 +1963,22 @@ config X86_INTEL_SHADOW_STACK_USER
>>>   
>>>   	  If unsure, say y.
>>>   
>>> +config X86_INTEL_BRANCH_TRACKING_USER
>>> +	prompt "Intel Indirect Branch Tracking for user-mode"
>>> +	def_bool n
>>> +	depends on CPU_SUP_INTEL && X86_64
>>> +	depends on $(cc-option,-fcf-protection)
>>> +	select X86_INTEL_CET
>>> +	help
>>> +	  Indirect Branch Tracking (IBT) provides protection against
>>> +	  CALL-/JMP-oriented programming attacks.  It is active when
>>> +	  the kernel has this feature enabled, and the processor and
>>> +	  the application support it.  When this feature is enabled,
>>> +	  legacy non-IBT applications continue to work, but without
>>> +	  IBT protection.
>>> +
>>> +	  If unsure, say y
>>
>> 	  If unsure, say y.
> 
> Actually, it would be "If unsure, say Y.", to be consistent with the
> rest of the Kconfig.
> 
> But I wonder if Yes by default is good idea. Only very new CPUs will
> support this, right? Are they even available at the market? Should the
> help text say "if your CPU is Whatever Lake or newer, ...." :-) ?

I will revise the wording if there is another version.  But a 
CET-capable kernel can run on legacy systems.  We have been testing that 
combination.

Yu-cheng