linux-kernel - Re: [PATCH v7 27/41] x86/mm: Warn if create Write=0,Dirty=1 with raw prot

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4D6EB652-3271-485E-A15B-0AE0FA98DFC7@kernel.org>
Date:   Mon, 27 Feb 2023 14:54:51 -0800
From:   Kees Cook <kees@...nel.org>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H . J . Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        John Allen <john.allen@....com>, kcc@...gle.com,
        eranian@...gle.com, rppt@...nel.org, jamorris@...ux.microsoft.com,
        dethoma@...rosoft.com, akpm@...ux-foundation.org,
        Andrew.Cooper3@...rix.com, christina.schimpe@...el.com,
        david@...hat.com, debug@...osinc.com
CC:     rick.p.edgecombe@...el.com
Subject: Re: [PATCH v7 27/41] x86/mm: Warn if create Write=0,Dirty=1 with raw prot

On February 27, 2023 2:29:43 PM PST, Rick Edgecombe <rick.p.edgecombe@...el.com> wrote:
>When user shadow stack is use, Write=0,Dirty=1 is treated by the CPU as
>shadow stack memory. So for shadow stack memory this bit combination is
>valid, but when Dirty=1,Write=1 (conventionally writable) memory is being
>write protected, the kernel has been taught to transition the Dirty=1
>bit to SavedDirty=1, to avoid inadvertently creating shadow stack
>memory. It does this inside pte_wrprotect() because it knows the PTE is
>not intended to be a writable shadow stack entry, it is supposed to be
>write protected.
>
>However, when a PTE is created by a raw prot using mk_pte(), mk_pte()
>can't know whether to adjust Dirty=1 to SavedDirty=1. It can't
>distinguish between the caller intending to create a shadow stack PTE or
>needing the SavedDirty shift.
>
>The kernel has been updated to not do this, and so Write=0,Dirty=1
>memory should only be created by the pte_mkfoo() helpers. Add a warning
>to make sure no new mk_pte() start doing this.
>
>Tested-by: Pengfei Xu <pengfei.xu@...el.com>
>Tested-by: John Allen <john.allen@....com>
>Tested-by: Kees Cook <keescook@...omium.org>
>Acked-by: Mike Rapoport (IBM) <rppt@...nel.org>
>Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>

Reviewed-by: Kees Cook <keescook@...omium.org>


-- 
Kees Cook