From: Peter Zijlstra <peterz@infradead.org>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
Rick P <rick.p.edgecombe@intel.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
the arch/x86 maintainers <x86@kernel.org>,
Kees Cook <kees@kernel.org>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Borislav Petkov <bp@alien8.de>, Thomas Gleixner <tglx@kernel.org>
Subject: Re: [RFC][PATCH 12/24] x86/cea: Map and use FRED exception shadow stacks
Date: Wed, 21 Oct 2026 23:40:57 +0200 [thread overview]
Message-ID: <20261021214057.GT2823843@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20261021195136.687DBEA2@davehans-spike.ostc.intel.com>
On Wed, Oct 21, 2026 at 12:51:36PM -0700, Dave Hansen wrote:
>
> FRED hardware automatically switches stacks between levels on different
> kinds of kernel entries. Each normal FRED "RSP" stack has a corresponding
> "SSP" shadow stack.
>
> Leverage the existing CPU Entry Area infrastructure. Add shadow stacks
> for levels 1-3 right next to the existing RSP stacks. Map them with
> shadow stack permissions. Last, point the FRED SSP MSRs at the exception
> stacks.
>
> Just like the task stacks, do not leave a guard page since regular and
> shadow stacks have mutually exclusive permissions and serve as guards
> for each other.
>
> Nit: The "return style" of the new cea_map_stack() and wrmsr() code
> looks superficially inconsistent. But each site is consistent with the
> code around it, just not when looking at the two sites against each
> other.
>
> == Future Work ==
>
> The *_stack_guard[] elements could probably be removed now. When in
> use, shadow stacks serve as guard pages for the regular stacks. When
> not in use, the shadow stack region could remain unmapped and also act
> as a guard area. But that would take some more fancy dynamic mapping
> work. The existing CEA code is dirt simple and doing anything dynamic
> would add complexity. KISS. The downside is wasting three pages per
> CPU when shadow stacks support is compiled in but not used at runtime.
People were trying to *shrink* stacks ;-)
next prev parent reply other threads:[~2026-10-21 21:41 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-21 19:51 [RFC][PATCH 00/24] x86 Kernel Shadow Stacks 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 [this message]
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
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