From: "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
To: Dave Hansen <dave.hansen@intel.com>, Jarkko Sakkinen <jarkko@kernel.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>, 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>,
Haitao Huang <haitao.huang@intel.com>
Subject: Re: [PATCH v22 8/8] x86/vdso: Add ENDBR64 to __vdso_sgx_enter_enclave
Date: Wed, 10 Mar 2021 15:22:41 -0800 [thread overview]
Message-ID: <727fed3a-f7da-a947-4221-56ab39deefe4@intel.com> (raw)
In-Reply-To: <c2bfe707-2ef6-213a-f02c-4689726a473a@intel.com>
On 3/10/2021 3:20 PM, Dave Hansen wrote:
> On 3/10/21 2:55 PM, Yu, Yu-cheng wrote:
>> On 3/10/2021 2:39 PM, Jarkko Sakkinen wrote:
>>> On Wed, Mar 10, 2021 at 02:05:19PM -0800, Yu-cheng Yu wrote:
>>>> When CET is enabled, __vdso_sgx_enter_enclave() needs an endbr64
>>>> in the beginning of the function.
>>>
>>> OK.
>>>
>>> What you should do is to explain what it does and why it's needed.
>>>
>>
>> The endbr marks a branch target. Without the "no-track" prefix, if an
>> indirect call/jmp reaches a non-endbr opcode, a control-protection fault
>> is raised. Usually endbr's are inserted by the compiler. For assembly,
>> these have to be put in manually. I will add this in the commit log if
>> there is another revision. Thanks!
>
> This is close, but it's missing a detail or two that I think is
> important for someone like Jarkko trying to figure out what it means for
> his subsystem or driver.
>
> I'd probably say:
>
> ENDBR is a special new instruction for the Indirect Branch Tracking
> (IBR) component of CET. IBT prevents attacks by ensuring that (most)
> indirect branches and function calls may only land at ENDBR
> instructions. Branches that don't follow the rules will result in
> control flow (#CF) exceptions.
>
> ENDBR is a noop when IBT is unsupported or disabled. Most ENDBR
> instructions are inserted automatically by the compiler, but branch
> targets written in assembly must have ENDBR added manually, like this one.
>
Ok, I will update. Thanks!
--
Yu-cheng
next prev parent reply other threads:[~2021-03-10 23:23 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-10 22:05 [PATCH v22 0/8] Control-flow Enforcement: Indirect Branch Tracking Yu-cheng Yu
2021-03-10 22:05 ` [PATCH v22 1/8] x86/cet/ibt: Update Kconfig for user-mode " Yu-cheng Yu
2021-03-10 22:05 ` [PATCH v22 2/8] x86/cet/ibt: User-mode Indirect Branch Tracking support Yu-cheng Yu
2021-03-10 22:05 ` [PATCH v22 3/8] x86/cet/ibt: Handle signals for Indirect Branch Tracking Yu-cheng Yu
2021-03-10 22:05 ` [PATCH v22 4/8] x86/cet/ibt: Update ELF header parsing " Yu-cheng Yu
2021-03-10 22:05 ` [PATCH v22 5/8] x86/cet/ibt: Update arch_prctl functions " Yu-cheng Yu
2021-03-10 22:05 ` [PATCH v22 6/8] x86/vdso/32: Add ENDBR32 to __kernel_vsyscall entry point Yu-cheng Yu
2021-03-10 22:05 ` [PATCH v22 7/8] x86/vdso: Insert endbr32/endbr64 to vDSO Yu-cheng Yu
2021-03-10 22:05 ` [PATCH v22 8/8] x86/vdso: Add ENDBR64 to __vdso_sgx_enter_enclave Yu-cheng Yu
2021-03-10 22:39 ` Jarkko Sakkinen
2021-03-10 22:55 ` Yu, Yu-cheng
2021-03-10 23:17 ` Borislav Petkov
2021-03-10 23:20 ` Dave Hansen
2021-03-10 23:22 ` Yu, Yu-cheng [this message]
2021-03-12 16:55 ` Jarkko Sakkinen
2021-03-12 16:57 ` Jarkko Sakkinen
2021-03-12 16:59 ` Dave Hansen
2021-03-11 3:36 ` Jarkko Sakkinen
2021-03-11 8:42 ` Peter Zijlstra
2021-03-11 15:44 ` Yu, Yu-cheng
2021-03-12 16:56 ` Jarkko Sakkinen
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