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X-CSE-ConnectionGUID: vScnc/LyQGOESa78Lt2V9g== X-CSE-MsgGUID: neydTAaeSHauUda7WyTX0Q== X-IronPort-AV: E=McAfee;i="6700,10204,11377"; a="43341566" X-IronPort-AV: E=Sophos;i="6.14,257,1736841600"; d="scan'208";a="43341566" Received: from fmviesa006.fm.intel.com ([10.60.135.146]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Mar 2025 07:48:52 -0700 X-CSE-ConnectionGUID: IQ3TbxkIR8KEyu06ZDzk0g== X-CSE-MsgGUID: wzMqsPulRTmvs9Yx8bMOVQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.14,257,1736841600"; d="scan'208";a="122114983" Received: from agladkov-desk.ger.corp.intel.com (HELO [10.125.109.198]) ([10.125.109.198]) by fmviesa006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Mar 2025 07:48:51 -0700 Message-ID: Date: Tue, 18 Mar 2025 07:48:50 -0700 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] /dev/mem: Disable /dev/mem under TDX guest To: Nikolay Borisov , dave.hansen@linux.intel.com Cc: kirill.shutemov@linux.intel.com, linux-coco@lists.linux.dev, x86@kernel.org, linux-kernel@vger.kernel.org, vannapurve@google.com References: <20250318113604.297726-1-nik.borisov@suse.com> Content-Language: en-US From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/18/25 04:36, Nikolay Borisov wrote: > 1. Should we forbid getting a descriptor to /dev/mem (this patch) > 2. Skip creating /dev/mem altogether3 Like Kirill mentioned, it would be nice to leverage the existing hooks: if (!capable(CAP_SYS_RAWIO)) return -EPERM; rc = security_locked_down(LOCKDOWN_DEV_MEM); if (rc) return rc; Lockdown seems like a decent fit. We'd also ideally check lockdown_is_locked_down() in x86 code and spew epithets if someone is booting a CoCo guest without lockdown. > 3. Possibly tinker with internals of ioremap to ensure that no memory which is > backed by kvm memslots is remapped as shared. It's not just memslots, though. It's any TDX private memory which includes stuff the TDX module uses like the PAMT or SEPT pages.