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Message-ID: <9fed0342-2d02-aaf2-ed66-20ff08bdfd0b@intel.com>
Date:   Fri, 30 Sep 2022 12:16:47 -0700
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Subject: Re: [PATCH v2 22/39] mm: Don't allow write GUPs to shadow stack
 memory
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To:     Rick Edgecombe <rick.p.edgecombe@intel.com>, 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>,
        Borislav Petkov <bp@alien8.de>,
        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>,
        "Ravi V . Shankar" <ravi.v.shankar@intel.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        joao.moreira@intel.com, John Allen <john.allen@amd.com>,
        kcc@google.com, eranian@google.com, rppt@kernel.org,
        jamorris@linux.microsoft.com, dethoma@microsoft.com
References: <20220929222936.14584-1-rick.p.edgecombe@intel.com>
 <20220929222936.14584-23-rick.p.edgecombe@intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <20220929222936.14584-23-rick.p.edgecombe@intel.com>
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On 9/29/22 15:29, Rick Edgecombe wrote:
> @@ -1633,6 +1633,9 @@ static inline bool __pte_access_permitted(unsigned long pteval, bool write)
>  {
>  	unsigned long need_pte_bits = _PAGE_PRESENT|_PAGE_USER;
>  
> +	if (write && (pteval & (_PAGE_RW | _PAGE_DIRTY)) == _PAGE_DIRTY)
> +		return 0;

Do we not have a helper for this?  Seems a bit messy to open-code these
shadow-stack permissions.  Definitely at least needs a comment.