Date:   Mon, 6 Mar 2023 14:10:17 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc:     x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-mm@kvack.org,
        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        "H . J . Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Weijiang Yang <weijiang.yang@intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        John Allen <john.allen@amd.com>, kcc@google.com,
        eranian@google.com, rppt@kernel.org, jamorris@linux.microsoft.com,
        dethoma@microsoft.com, akpm@linux-foundation.org,
        Andrew.Cooper3@citrix.com, christina.schimpe@intel.com,
        david@redhat.com, debug@rivosinc.com
Subject: Re: [PATCH v7 24/41] mm: Don't allow write GUPs to shadow stack
 memory
Message-ID: <ZAXmOZYcoR3hq/CH@zn.tnic>
References: <20230227222957.24501-1-rick.p.edgecombe@intel.com>
 <20230227222957.24501-25-rick.p.edgecombe@intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20230227222957.24501-25-rick.p.edgecombe@intel.com>
Precedence: bulk

On Mon, Feb 27, 2023 at 02:29:40PM -0800, Rick Edgecombe wrote:
> The x86 Control-flow Enforcement Technology (CET) feature includes a new
> type of memory called shadow stack. This shadow stack memory has some
> unusual properties, which requires some core mm changes to function
> properly.
> 
> Shadow stack memory is writable only in very specific, controlled ways.
> However, since it is writable, the kernel treats it as such. As a result
									  ^
									  ,

> there remain many ways for userspace to trigger the kernel to write to
> shadow stack's via get_user_pages(, FOLL_WRITE) operations. To make this a

"stacks"

or "to write to a shadow stack via..."

> little less exposed, block writable GUPs for shadow stack VMAs.

GUPs?

I supposed this means "prevent get_user_pages() from pinning pages to
which the corresponding VMA is a shadow stack one."?

Or something like that which is less mm-internal speak...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette