From: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>
Cc: "peterz@infradead.org" <peterz@infradead.org>,
"kees@kernel.org" <kees@kernel.org>,
"tglx@kernel.org" <tglx@kernel.org>,
"pawan.kumar.gupta@linux.intel.com"
<pawan.kumar.gupta@linux.intel.com>,
"luto@kernel.org" <luto@kernel.org>,
"x86@kernel.org" <x86@kernel.org>, "bp@alien8.de" <bp@alien8.de>
Subject: Re: [RFC][PATCH 00/24] x86 Kernel Shadow Stacks
Date: Fri, 23 Oct 2026 02:52:11 +0000 [thread overview]
Message-ID: <ea3a79b7b91a9f2e6c7c4c351162542e87b721b6.camel@intel.com> (raw)
In-Reply-To: <c8accd0f-118e-49ae-839d-7474250b14e4@citrix.com>
On Fri, 2026-10-23 at 03:21 +0100, Andrew Cooper wrote:
> > * Add a "warn on #CP and continue". Good for debugging. But, bad
> > for security. Ideally, a secure kernel would have no easy to
> > reach gadgets to disable shadow stacks.
>
> This looks attractive at first glance, but it's really not. There is no
> safe way to turn CET-SS off.
>
> WRSS, RSTORSSP and INCSSP will #UD when you turn CET-SS off, and even
> logic such as
>
> if (!ssef)
> return;
> wrss(ip, &ssef->ssef_lip);
>
> in regs_set_return_ip() will die with a #UD as you're attempting to not
> die from a #CP.
Yea.
>
> I suggest just leave CET-SS on and power through the reports. It will
> probably be faster overall, and it will definitely be a better end result.
It still can't remove all side effects though. Like if your shadow stack issue
is causing underflowing the shadow stack you will get a #PF instead of #CP.
I think there is just various levels of best efforts you can do to keep things
functional.
prev parent reply other threads:[~2026-10-23 2:52 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-21 19:51 Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 01/24] kernel/fork: Break out vmap task allocation into helper Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 02/24] kernel/fork: Use sizeof() union instead of TASK_SIZE Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 03/24] kernel/sched: Move thread stack to its own structure Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 04/24] kernel/fork: Allow arch-specific stack initialization Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 05/24] kernel/task: Add shadow stack to thread structure Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 06/24] kernel/task: Add "runtime" check for shadow stack support Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 07/24] kernel/fork: Clear shadow stacks alongside normal stacks Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 08/24] x86/cpu: Add basic x86 kernel shadow stack infrastructure Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 09/24] x86/cea: Refactor "CEA" macros to deal with multiple stacks Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 10/24] x86/cea: Refactor stack mapping macros Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 11/24] x86/mm: Add kernel shadow stack permission macros Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 12/24] x86/cea: Map and use FRED exception shadow stacks Dave Hansen
2026-10-21 21:40 ` Peter Zijlstra
2026-10-21 22:59 ` Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 13/24] x86/task: Grow thread_union for " Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 14/24] x86/mm: Establish shadow stack permissions in thread mapping Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 15/24] x86/task: Hook up arch hook to detect shadow stack enabling Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 16/24] x86/mm: Kill shadow stack page permission warning Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 17/24] x86/task: Context switch the kernel shadow stack register value Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 18/24] kernel/task: Add a helper to get the thread_union Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 19/24] x86/process: Initialize cloned task shadow stack Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 20/24] x86/entry: Stash kernel SSP on FRED entry Dave Hansen
2026-10-22 22:14 ` Andrew Cooper
2026-10-21 19:51 ` [RFC][PATCH 21/24] x86/extable: Update shadow stack entry frame during RIP overwrites Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 22/24] kernel/task: Add a helper to locate the top of the shadow stack Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 23/24] x86/entry: Populate FRED register for user=>kernel transitions Dave Hansen
2026-10-21 19:51 ` [RFC][PATCH 24/24] [DO NOT MERGE] x86/shstk: Depend out everything incompatible with kernel shadow stacks Dave Hansen
2026-10-22 21:35 ` Andrew Cooper
2026-10-22 21:38 ` Andrew Cooper
2026-10-21 21:36 ` [RFC][PATCH 00/24] x86 Kernel Shadow Stacks Peter Zijlstra
2026-10-21 21:53 ` Peter Zijlstra
2026-10-23 2:21 ` Andrew Cooper
2026-10-23 2:52 ` Edgecombe, Rick P [this message]
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