Re: [PATCH v27 24/31] x86/cet/shstk: Handle thread shadow stack - Yu, Yu-cheng

From: "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
To: Florian Weimer <fweimer@redhat.com>, John Allen <john.allen@amd.com>
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>,
	"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>,
	"Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Subject: Re: [PATCH v27 24/31] x86/cet/shstk: Handle thread shadow stack
Date: Wed, 21 Jul 2021 11:34:53 -0700	[thread overview]
Message-ID: <ee98275e-cd1d-ad94-73cd-470bf89ca344@intel.com> (raw)
In-Reply-To: <87h7gnldx4.fsf@oldenburg.str.redhat.com>

On 7/21/2021 11:28 AM, Florian Weimer wrote:
> * John Allen:
> 
>> At the very least, it would seem that on some systems, it isn't valid to
>> rely on the stack_size passed from clone3, though I'm unsure what the
>> correct behavior should be here. If the passed stack_size == 0 and sp ==
>> 0, is this a case where we want to alloc a shadow stack for this thread
>> with some capped size? Alternatively, is this a case that isn't valid to
>> alloc a shadow stack and we should simply return 0 instead of -EINVAL?
>>
>> I'm running Fedora 34 which satisfies the required versions of gcc,
>> binutils, and glibc.
> 
> Fedora 34 doesn't use clone3 yet.  You can upgrade to a rawhide build,
> e.g. glibc-2.33.9000-46.fc35:
> 
>    <https://koji.fedoraproject.org/koji/buildinfo?buildID=1782678>
> 
> It's currently not in main rawhide because the Firefox sandbox breaks
> clone3.  The “fix” is that clone3 will fail with ENOSYS under the
> sandbox.
> 
> I expect that container runtimes turn clone3 into clone in the same way
> (via ENOSYS), at least for the medium term.  So it would make sense to
> allocate some sort of shadow stack for clone as well, if that's possible
> to implement in some way.
> 
> Thanks,
> Florian
> 

Thanks Florian!  And because of that reason, we will put back clone2 
support in my next v28 patches.

Yu-cheng