From: Dave Hansen <dave.hansen@intel.com>
To: Peter Zijlstra <peterz@infradead.org>,
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 15:59:32 -0700 [thread overview]
Message-ID: <265c8e12-bf90-4fcf-927a-0de1f29c55b6@intel.com> (raw)
In-Reply-To: <20261021214057.GT2823843@noisy.programming.kicks-ass.net>
On 10/21/26 14:40, Peter Zijlstra wrote:
>> == 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 😉
Heh. I'll leave this one as an exercise to the reader if folks really care.
They can either allocate the physical space in the percpu areas like it
is now and try to free it later. Or, they can treat the cea virtual
space like a hole that needs to have a mapping placed in it later.
next prev parent reply other threads:[~2026-10-21 22:59 UTC|newest]
Thread overview: 29+ 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
2026-10-21 22:59 ` Dave Hansen [this message]
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
2026-10-21 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
2026-10-21 21:36 ` [RFC][PATCH 00/24] x86 Kernel Shadow Stacks Peter Zijlstra
2026-10-21 21:53 ` Peter Zijlstra
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