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30 Sep 2022 13:37:57 -0700 X-IronPort-AV: E=McAfee;i="6500,9779,10486"; a="951683520" X-IronPort-AV: E=Sophos;i="5.93,358,1654585200"; d="scan'208";a="951683520" Received: from lzearing-mobl.amr.corp.intel.com (HELO [10.209.49.67]) ([10.209.49.67]) by fmsmga005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Sep 2022 13:37:55 -0700 Message-ID: <5994adb0-12b7-b8f1-ecdc-ebf56af48947@intel.com> Date: Fri, 30 Sep 2022 13:37:54 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v2 22/39] mm: Don't allow write GUPs to shadow stack memory Content-Language: en-US To: "Edgecombe, Rick P" , "Shankar, Ravi V" , "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "peterz@infradead.org" , "rdunlap@infradead.org" , "keescook@chromium.org" , "dave.hansen@linux.intel.com" , "kirill.shutemov@linux.intel.com" , "Eranian, Stephane" , "linux-mm@kvack.org" , "fweimer@redhat.com" , "nadav.amit@gmail.com" , "jannh@google.com" , "dethoma@microsoft.com" , "linux-arch@vger.kernel.org" , "kcc@google.com" , "bp@alien8.de" , "oleg@redhat.com" , "hjl.tools@gmail.com" , "Yang, Weijiang" , "Lutomirski, Andy" , "pavel@ucw.cz" , "arnd@arndb.de" , "Moreira, Joao" , "tglx@linutronix.de" , "mike.kravetz@oracle.com" , "x86@kernel.org" , "linux-doc@vger.kernel.org" , "jamorris@linux.microsoft.com" , "john.allen@amd.com" , "rppt@kernel.org" , "mingo@redhat.com" , "corbet@lwn.net" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "gorcunov@gmail.com" References: <20220929222936.14584-1-rick.p.edgecombe@intel.com> <20220929222936.14584-23-rick.p.edgecombe@intel.com> <9fed0342-2d02-aaf2-ed66-20ff08bdfd0b@intel.com> <44314145f644ab822ac36cc8c78520d5f34d5bd8.camel@intel.com> From: Dave Hansen In-Reply-To: <44314145f644ab822ac36cc8c78520d5f34d5bd8.camel@intel.com> Content-Type: text/plain; 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bh=mLpYiECGaTgfWI7723UoTzwSHUEWX4x3iZ011nnFV5I=; b=LVgRtgGT2Gsh/sh1iRzyEn4H7ej0DDS1PAMXJT9Rw39GJCXZ9r8ptiwWYhduCTVysVrbZr tZXQ+r8juSqk4GiD+U4Nv2lhJEDFmu3cos1cStgrb3oRylmt7qfnUmd71rgX+z0ZG0uBQg +lAkviq6oVkU3bFhB51C5ZMZDc3c8vk= X-Stat-Signature: z4g55tgjc94ph68wdx7mxwbf7uehfp64 X-Rspamd-Queue-Id: 978DE1A000F X-Rspamd-Server: rspam04 Authentication-Results: imf19.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b="LEvvm1g/"; dmarc=pass (policy=none) header.from=intel.com; spf=pass (imf19.hostedemail.com: domain of dave.hansen@intel.com designates 134.134.136.65 as permitted sender) smtp.mailfrom=dave.hansen@intel.com X-Rspam-User: X-HE-Tag: 1664570278-423002 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 9/30/22 13:30, Edgecombe, Rick P wrote: > On Fri, 2022-09-30 at 12:16 -0700, Dave Hansen wrote: >> 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. > It's because pteval is an unsigned long. We could create a pte_t, and > use the helpers, but then we would be using pte_foo() on pmd's, etc. So > probably comment is the better option? Yeah, a comment is probably best. This is one of those "generic" page table functions that doesn't work well with the p{te,md,ud}_* types. It's either this or cast over to a pteval_t for pmd/pud and pretend this is a pte-only function.