From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E4B8CC636CC for ; Mon, 13 Feb 2023 20:01:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229643AbjBMUBS (ORCPT ); Mon, 13 Feb 2023 15:01:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38486 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229795AbjBMUBN (ORCPT ); Mon, 13 Feb 2023 15:01:13 -0500 Received: from mail-pl1-x630.google.com (mail-pl1-x630.google.com [IPv6:2607:f8b0:4864:20::630]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8757017176 for ; Mon, 13 Feb 2023 12:01:12 -0800 (PST) Received: by mail-pl1-x630.google.com with SMTP id z1so14688542plg.6 for ; Mon, 13 Feb 2023 12:01:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20210112.gappssmtp.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=w/ylDHJlU1BFl20coGEiz1808doT/68HrQMyJm0KLIY=; b=pXRJHdDi1FBiTWcyaGAee5cATMQnJvUp3NbKoj+XlSja5seq3XzvjkeO0qeYppE1ui eZqKh0rOjjZEQSLvUv8oKMnsHLkM0WawTpLFFV8ZjaYqLpcb7HfIyJEexzh3hbeXl0Dn LuyZZUw6nIzFtxuSfFJVUUARRsFc12DuBqH6rNcEGnD4IoX+o9EfThkdZ2JebFH3gYmP CRW+PqwqyV+XkvO5FV4DXIhtX9Aq3cAqJdHEU3UXPX7BgDeRTH4Lv7UZm4sDVHm63ZSq xiYbHdEu1+BAZbxQrB8ADcvkUUhOEbtmP542VDbIDL5c+PWelWzPOKXIdP7iUQMfVTdI GDBg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=w/ylDHJlU1BFl20coGEiz1808doT/68HrQMyJm0KLIY=; b=J9M6SAIt5K46+l0xuFYnooaowRi65XTWpUeQSaJMU0uaVaJIGa6nd4OFWH4ta/MFjh hvc322gZTD+vVaHLgO5AJ/FmnkhSR7YyDnpJxYtXyfF0ZcLlgI1j83QjwiYxYqpcuOSG AQw+7WpVBZK+4VUeWnbdxC0zVul7IjBlbjMwR7T+XmBfC/Usjr0jnDnM1y+ALFIMSWmV kYKZIx3fBVeOtWKhp2ho2yqBY8DdUUMio/GXJDKNm7BzZ9ZDQvJFgn/6RgHbtp7WYxuF rd+pj7hl7C+E5No7eCZs0KmyjeRCIJLUKPefMT5uKhbcwUsYTnUpIj4U+WTPbnUoxjmw Doew== X-Gm-Message-State: AO0yUKV1GceaGfpeWl1UpwbybZP+lQRX/g7TH4eayaf3h8AuhgnR5xpd B9wbitn+nWXRYY05EG4NSTOPug== X-Google-Smtp-Source: AK7set+IUYie8T4ysBZbfM8RDgBJuy1q7vvaVvTl80/SQVMK6LuRzrIIVld8uHAf7Br81bxAQGwapw== X-Received: by 2002:a17:902:f304:b0:19a:85a7:dcb9 with SMTP id c4-20020a170902f30400b0019a85a7dcb9mr114129ple.2.1676318471954; Mon, 13 Feb 2023 12:01:11 -0800 (PST) Received: from debug.ba.rivosinc.com ([66.220.2.162]) by smtp.gmail.com with ESMTPSA id t23-20020a170902b21700b00196047fc25dsm8630945plr.42.2023.02.13.12.01.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 13 Feb 2023 12:01:11 -0800 (PST) Date: Mon, 13 Feb 2023 12:01:09 -0800 From: Deepak Gupta To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Andrew Morton , linux-mm@kvack.org Subject: Re: [PATCH v1 RFC Zisslpcfi 11/20] mmu: maybe_mkwrite updated to manufacture shadow stack PTEs Message-ID: <20230213200109.GA4016181@debug.ba.rivosinc.com> References: <20230213045351.3945824-1-debug@rivosinc.com> <20230213045351.3945824-12-debug@rivosinc.com> <2d6eefb8-c7c5-7d32-9a75-ae716f828cd9@redhat.com> <20230213143754.GC3943238@debug.ba.rivosinc.com> <7693247c-a55d-a375-3621-1b07115a9d99@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <7693247c-a55d-a375-3621-1b07115a9d99@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 13, 2023 at 03:56:22PM +0100, David Hildenbrand wrote: >On 13.02.23 15:37, Deepak Gupta wrote: >>On Mon, Feb 13, 2023 at 01:05:16PM +0100, David Hildenbrand wrote: >>>On 13.02.23 05:53, Deepak Gupta wrote: >>>>maybe_mkwrite creates PTEs with WRITE encodings for underlying arch if >>>>VM_WRITE is turned on in vma->vm_flags. Shadow stack memory is a write- >>>>able memory except it can only be written by certain specific >>>>instructions. This patch allows maybe_mkwrite to create shadow stack PTEs >>>>if vma is shadow stack VMA. Each arch can define which combination of VMA >>>>flags means a shadow stack. >>>> >>>>Additionally pte_mkshdwstk must be provided by arch specific PTE >>>>construction headers to create shadow stack PTEs. (in arch specific >>>>pgtable.h). >>>> >>>>This patch provides dummy/stub pte_mkshdwstk if CONFIG_USER_SHADOW_STACK >>>>is not selected. >>>> >>>>Signed-off-by: Deepak Gupta >>>>--- >>>> include/linux/mm.h | 23 +++++++++++++++++++++-- >>>> include/linux/pgtable.h | 4 ++++ >>>> 2 files changed, 25 insertions(+), 2 deletions(-) >>>> >>>>diff --git a/include/linux/mm.h b/include/linux/mm.h >>>>index 8f857163ac89..a7705bc49bfe 100644 >>>>--- a/include/linux/mm.h >>>>+++ b/include/linux/mm.h >>>>@@ -1093,6 +1093,21 @@ static inline unsigned long thp_size(struct page *page) >>>> void free_compound_page(struct page *page); >>>> #ifdef CONFIG_MMU >>>>+ >>>>+#ifdef CONFIG_USER_SHADOW_STACK >>>>+bool arch_is_shadow_stack_vma(struct vm_area_struct *vma); >>>>+#endif >>>>+ >>>>+static inline bool >>>>+is_shadow_stack_vma(struct vm_area_struct *vma) >>>>+{ >>>>+#ifdef CONFIG_USER_SHADOW_STACK >>>>+ return arch_is_shadow_stack_vma(vma); >>>>+#else >>>>+ return false; >>>>+#endif >>>>+} >>>>+ >>>> /* >>>> * Do pte_mkwrite, but only if the vma says VM_WRITE. We do this when >>>> * servicing faults for write access. In the normal case, do always want >>>>@@ -1101,8 +1116,12 @@ void free_compound_page(struct page *page); >>>> */ >>>> static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) >>>> { >>>>- if (likely(vma->vm_flags & VM_WRITE)) >>>>- pte = pte_mkwrite(pte); >>>>+ if (likely(vma->vm_flags & VM_WRITE)) { >>>>+ if (unlikely(is_shadow_stack_vma(vma))) >>>>+ pte = pte_mkshdwstk(pte); >>>>+ else >>>>+ pte = pte_mkwrite(pte); >>>>+ } >>>> return pte; >>> >>>Exactly what we are trying to avoid in the x86 approach right now. >>>Please see the x86 series on details, we shouldn't try reinventing the >>>wheel but finding a core-mm approach that fits multiple architectures. >>> >>>https://lkml.kernel.org/r/20230119212317.8324-1-rick.p.edgecombe@intel.com >> >>Thanks David for comment here. I looked at x86 approach. This patch >>actually written in a way which is not re-inventing wheel and is following >>a core-mm approach that fits multiple architectures. >> >>Change above checks `is_shadow_stack_vma` and if it returns true then only >>it manufactures shadow stack pte else it'll make a regular writeable mapping. >> >>Now if we look at `is_shadow_stack_vma` implementation, it returns false if >>`CONFIG_USER_SHADOW_STACK` is not defined. If `CONFIG_USER_SHADOW_STACK is >>defined then it calls `arch_is_shadow_stack_vma` which should be implemented >>by arch specific code. This allows each architecture to define their own vma >>flag encodings for shadow stack (riscv chooses presence of only `VM_WRITE` >>which is analogous to choosen PTE encodings on riscv W=1,R=0,X=0) >> >>Additionally pte_mkshdwstk will be nop if not implemented by architecture. >> >>Let me know if this make sense. If I am missing something here, let me know. > >See the discussion in that thread. The idea is to pass a VMA to >pte_mkwrite() and let it handle how to actually set it writable. > Thanks. I see. Instances where `pte_mkwrite` is directly invoked by checking VM_WRITE and thus instead of fixing all those instance, make pte_mkwrite itself take vma flag or vma. I'll revise. >-- >Thanks, > >David / dhildenb >