From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 B74A61DB120 for ; Fri, 24 Jan 2025 08:52:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737708734; cv=none; b=hQJvi3s64R/mrbiRbF3MC9OWkfwRN+s7lXX9Jwp1gWuPGyQtjah2I8n7XncbWi+cLdwgrEFhPqXmTauC/0LGrd5p+Wqx3qe8jI0F4qOefAwUzfNBcerlwv/XlS1NqdhxWTvSvq26JQzn9DdsQWP0N8omJalD9MGLkw8pkRdJ3oo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737708734; c=relaxed/simple; bh=lTRAFcDBN+wZbmEHk8LRJ80vOy6QkHI3bmEBMSaFBWE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=eNuXcW+OrXbF6mWaUzHS2Mo1krHdnUc2jdZo1qOoYssRLs5L8TI5/HH0Hh7WNdeB2gYaPbF7feKSEFVhCWVBU/5SpkrVD1h5qYZU0HinHGG9mMXD0uLzsDtplO5heJ+D3mg5P6qq3Mk1f6WJRnNPns4wR+LVI8eIsttjXjJmm3k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=RcXRc7PK; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="RcXRc7PK" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=6nIiH34XyvQUksyy/tfwQk/fEldqPQkD0cRRWWJBLqE=; b=RcXRc7PK/zmVRzwAIoQYZq0EPG 22BW8vqQTyzawtYcAqU1s73l3+ji+m485FfRbyBiJ6wlQR6ZW2CHpQPCW1YgQocof8M9lo0ab8moI PLGvU5V5sP39GeGgjvYeYfrIOjUD9+YtTG+SrwQU0eo7LRPaBtcHX1EK8XzoFTczjFh0Pr/oQ8dtF lctK6Ey99tIdPhcBdPU4OUJMRmR7KV9/Bnh52bbs1Ix1MR4TfS5re28Q2xzx2+ahY9IFnnGiZ49WJ 8XH9awklH9MT2bQGqaSyS7+QYMr9eA1jEAaLCwOSopdmmCFnYAYU3txbVB/aarejyIwWC/l0d/5X0 WcrPOfQQ==; Received: from 77-249-17-89.cable.dynamic.v4.ziggo.nl ([77.249.17.89] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tbFQ3-0000000Dyfo-23wJ; Fri, 24 Jan 2025 08:52:04 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id E0644300677; Fri, 24 Jan 2025 09:52:02 +0100 (CET) Date: Fri, 24 Jan 2025 09:52:02 +0100 From: Peter Zijlstra To: Dave Hansen Cc: Dave Hansen , linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de, bp@alien8.de, joro@8bytes.org, luto@kernel.org, kirill.shutemov@linux.intel.com, rick.p.edgecombe@intel.com, jgross@suse.com Subject: Re: [RFC][PATCH 0/8] x86/mm: Simplify PAE page table handling Message-ID: <20250124085202.GC13226@noisy.programming.kicks-ass.net> References: <20250123172428.D6D8C8D9@davehans-spike.ostc.intel.com> <20250123214911.GB969@noisy.programming.kicks-ass.net> <6c1785c8-e74e-4912-95bb-88b6e94f544f@intel.com> 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=us-ascii Content-Disposition: inline In-Reply-To: <6c1785c8-e74e-4912-95bb-88b6e94f544f@intel.com> On Thu, Jan 23, 2025 at 03:06:26PM -0800, Dave Hansen wrote: > On 1/23/25 13:49, Peter Zijlstra wrote: > > Can't we just rip it out? > > 32-bit+PTI or 32-bit in general? ;) Yes :-) > I'm curious what Joerg and the other folks that worked on 32-bit PTI > think about it in retrospect. The 32 vs. 64-bit security gap was > probably modest in 2018 and it can only have grown since then. > > I definitely haven't seen a lot of 32-bit PTI bug reports. 3db03fb4995e x86/mm: Fix pti_clone_entry_text() for i386 41e71dbb0e0a x86/mm: Fix pti_clone_pgtable() alignment assumption Them cost me a few gray hairs :-) Anyway, 32bit PTI is 'solid', it's just all the other speculation mitigations what we've added to x86_64 only since. Even the retpoline crap on i386, that is still vulnerable to the whole funnel thing, so while it has the OG retpoline, it is still vulnerable to more modern attacks that abuse the fact that all indirect jumps come from only a single location. So yes, we patches a few (early) holes on i386, but nobody should be thinking i386 is 'secure' from all this speculation nonsense. What's the point of having a few holes patched, if you're still bleeding from a dozen others :/ So if we keep i386 around, it might just make sense to rip out all speculation mitigations -- no point pretending.