From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-108-mta202.mxroute.com (mail-108-mta202.mxroute.com [136.175.108.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 82E193FDBE7 for ; Mon, 18 May 2026 16:25:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=136.175.108.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779121560; cv=none; b=Lz4bSlhMttXe6ZpniI3LagdmyKiXMzkhBODFBDOmfUtBVW+NL7PG5dUVjYKyOHEJHp0mOwdM6juioQHCAcJoYLkEdPLu5XHpC9l0eJYgd1jsjtSNcGqUNjgGXqQjIqCOjRr5MqbkveSsAU+5BPnFs0aZo0EGKNdABJiIB0WclnA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779121560; c=relaxed/simple; bh=0BPmgMtJS+bcF+/mesQQXQyUq8KaoDpdOp1lJOPwks8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ioKjNrf/JoEcGPX3KbmG0NcZWEL8rLi3dxPXBW7Av5v0mHwMZIDUWdJXkE8YxYt3VJ9CGB7cqm9nO8CAJN5TwEnB3IWKWODY8Nt1qlbIWsXUTRKS7YW0ffP2srBmiyzvMe9sZdziH1MBRz9drjTKT/bCT0o69bNvvNazmikLHB0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=wii.dev; spf=pass smtp.mailfrom=wii.dev; dkim=pass (2048-bit key) header.d=wii.dev header.i=@wii.dev header.b=D9KhCic8; arc=none smtp.client-ip=136.175.108.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=wii.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=wii.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=wii.dev header.i=@wii.dev header.b="D9KhCic8" Received: from filter006.mxroute.com ([136.175.111.3] filter006.mxroute.com) (Authenticated sender: mN4UYu2MZsgR) by mail-108-mta202.mxroute.com (ZoneMTA) with ESMTPSA id 19e3be884fb00067f7.00d for (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384); Mon, 18 May 2026 16:25:54 +0000 X-Zone-Loop: 867fff870f6be7140c1c29175d53b0deb5e9d3c88f28 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=wii.dev; s=x; 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:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=qnSxJKEl0qRPArxjJpQ7k4Ogs6rey6KiQ78uKuOSg9s=; b=D9KhCic8jBwhkAzRIy/FQuz/SU 3Tzo1JQahaiLepIv9gotvicNZu08ujluNWhyek4IEKCdfZmeqsJoGzz0FGz/raqa2yONt1EZXeoW7 7IELTE2mj5YW0Gu2dOKPp8zoXeqxi/9X9AEGvv0itCWCD7wClKSgnBI85/QFEmIzRBqUsaZhDqiUk qzaVk2hXGI0Iyl48pp5npGTpJWtRzbufEXaekZ8nrhPjfSeBnzCAnjxRe4nu2qphAI7cCe+sXtHfY Lz5zdh5Lck0L8G9i1ZchtEMan7kE+Tbqnvmyhq0/rbft2r2qauorHiElTuSjjHW9CjgBlViIde0TN anmx9hUQ==; Date: Mon, 18 May 2026 16:25:40 +0000 From: Richard Patel To: Peter Zijlstra Cc: x86@kernel.org, Rick Edgecombe , Yu-cheng Yu , Dave Hansen , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Andy Lutomirski , Kees Cook , Shuah Khan , linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/7] Usermode Indirect Branch Tracking Message-ID: References: <20260517183024.16292-1-ripatel@wii.dev> <20260518073616.GQ3102624@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kselftest@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: <20260518073616.GQ3102624@noisy.programming.kicks-ass.net> X-Authenticated-Id: ripatel@wii.dev On Mon, May 18, 2026 at 09:36:16AM +0200, Peter Zijlstra wrote: > Anyway, the most contentious part was the whole backwards compat bitmap > crap. When the dynamic linker composes a process of parts that support > IBT and parts that do not, you get to deal with fallout. Is it acceptable to do all-or-nothing IBT first? And then do a second round of patches with legacy support? Until then, ld.so could: - start with IBT, disable it upon loading incompatible DSO - allow users to manually lock IBT I thought this weak form of IBT is better than nothing at all, if there's a risk that legacy support derails things. Btw, apparently OpenBSD enforces kernel+user IBT. I think the end goal is a user_ibt=force command-line param that locks IBT for all processes on startup. > The IBT spec has this horrid bitmap thing to try and deal with this, and > those early patches exposed that piece of shit to userspace. Then later > patches (suggested by me) used the ARM64/BTI approach of using PROT_BTI. > We'd use a (software) page-table bit, and upon #CP consult that to see > if we should eat the trap or produce a warn/signal whatever. Nice, I'm happy to revive/rebase/test any of this if there's interest. > I think we were near something workable there when Rick got pulled from > this and put onto something more 'important' and things just haven't > moved ever since. > > Anyway, glad to see someone has time to poke at this. Happy to spend whatever time is needed to land IBT. I'm very glad the first reaction wasn't "absolutely no way" :-) Thank you, -Richard