From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EB45D244685 for ; Sat, 20 Jun 2026 22:00:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781992801; cv=none; b=Z4K/7Se7rS70lFIIttC+1cj7Est7mtAV9a1wj7lWtish/Zyp90LyuloiaaYdmiJvEo/YA8lL334hPudzOZl1/jb2R4ELdXdzm6SHkJ/Wqo6ovEBlLvJBkZ5XtrXpdrfkbXWqsNsaRyXm/XvlyPP8/rg0ynVl7F68C9ErwgBW8v0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781992801; c=relaxed/simple; bh=Hmd66ETe+KdN/GYyC1WeLj72CkxszajSgdR1cawIbxg=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=LXPsPav+kLPbLHgyXlLmdeG7VqYi4Nom2GixHm49DbjoYrKf6ySL+mzLhS7ExTAAhbjiH3xm32keOA3xAOcjf4STHCloG9tElAZHJFsE+UAazzXIWiOcNm22s1LfObiZjuOHNL3awFGE/u1U22654VcR+OxTlArR+I6J5iu1T8g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=h9PwQS4e; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="h9PwQS4e" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CDFC51F000E9; Sat, 20 Jun 2026 21:59:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781992800; bh=tDJ33uOBr59BAp/p2vfEcH2XbwYYJbL8kVvEXKlUrLA=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=h9PwQS4etwPbAg9X2ufL4llCHlsEGgXRKFxLf0paQ1BatbX471sarP1Hr5epLyFV+ aK4CUkuXrN/eh8KzC2flQhazihb50wVyjEslO8yT8drbWxzlSHZn6XoSkvHgNWiFL4 JPFraZpq3DgZ1PwE1RXzZCElzchoUdxGPFYcXnYKBCoLEKEzKTaX6uRjnDmn5b20Eu cmT91luAAjGnEXpas+kc6Grz6gVgWXECc/6pUVassD47ERWE3gAwtX8ViX4CXPUckR u8P9/NC/KsIhgVkNsRnqoc53kdMNNI3M5WzMN1KCv/VZZm7FcP/0fD9xTJlTtXkVHL hJxAv2t9cjwPg== From: Thomas Gleixner To: David Stevens Cc: Zach O'Keefe , Dave Hansen , "H. Peter Anvin" , Pasha Tatashin , Linus Walleij , Will Deacon , Quentin Perret , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Andy Lutomirski , Xin Li , Peter Zijlstra , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , Kees Cook , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 00/13] Dynamic Kernel Stacks In-Reply-To: References: <20260424191456.2679717-1-stevensd@google.com> <6369e5ce-74e3-4c68-8053-d7d7d21b6955@zytor.com> <87pl1md7h0.ffs@fw13> <87qzm2b39k.ffs@fw13> Date: Sat, 20 Jun 2026 23:59:57 +0200 Message-ID: <87pl1kna8y.ffs@fw13> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On Fri, Jun 19 2026 at 22:02, David Stevens wrote: > On Fri, Jun 19, 2026 at 2:59=E2=80=AFPM Thomas Gleixner = wrote: >> If the kernel skips a whole page or more then there is a serious bug >> somewhere. I might be missing something, but again the "very unlikely" >> wording which handwaves about it is just disgustingly useless. > > FRAME_WARN accepts values up to 8192 bytes, and it can always be > ignored or simply disabled. If a stack frame is larger than 4k, then We should limit that to something sane. > it's entirely possible for the code and compiler to align in a way > where the first access in the frame skips a page in the stack. I think > we agree that such code would be highly suspect and (hopefully) would > only exist in out-of-tree drivers. We don't care about out of tree drivers. > But it's something the kernel build system accepts today. Dynamic > kernel stacks suddenly turning that into a runtime kernel panic seems > like exactly the sort of edge case that we would get yelled at for not > addressing. That's a good thing. If it breaks in tree code then those people have finally an incentive to fix the warnings sent by the robots which they ignored for a long time. If it breaks out of tree code then *SHRUG*. We guarantee not to break user space, but we don't guarantee anything for out of tree kernel hacks. Thanks, tglx