Re: [PATCH v18 21/25] x86/cet/shstk: Handle signals for shadow stack - Yu, Yu-cheng

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>
Subject: Re: [PATCH v18 21/25] x86/cet/shstk: Handle signals for shadow stack
Date: Mon, 1 Feb 2021 14:58:19 -0800	[thread overview]
Message-ID: <21462baa-8924-f005-33e1-f5fa36ed9942@intel.com> (raw)
In-Reply-To: <09da02c5-c6fb-878e-ad34-222f3a152460@intel.com>

On 2/1/2021 2:53 PM, Dave Hansen wrote:
> On 1/27/21 1:25 PM, Yu-cheng Yu wrote:
>> To deliver a signal, create a shadow stack restore token and put a restore
>> token and the signal restorer address on the shadow stack.  For sigreturn,
>> verify the token and restore the shadow stack pointer.
>>
>> Introduce WRUSS, which is a kernel-mode instruction but writes directly to
>> user shadow stack.  It is used to construct the user signal stack as
>> described above.
>>
>> Introduce a signal context extension struct 'sc_ext', which is used to save
>> shadow stack restore token address and WAIT_ENDBR status.  WAIT_ENDBR will
>> be introduced later in the Indirect Branch Tracking (IBT) series, but add
>> that into sc_ext now to keep the struct stable in case the IBT series is
>> applied later.
> 
> This changelog needs some work.  It's got a lot of "what" and not enough
> "why".
> 
> Why do we need a token?
> What function does it serve?
> What does it protect against?
> Why do we need a signal context extension?
> 

I will update it.

--
Yu-cheng