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(p200300e5873ca5006aafb7a77c29ae5c.dip0.t-ipconnect.de. [2003:e5:873c:a500:6aaf:b7a7:7c29:ae5c]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a5a17b17cc5sm1118947466b.205.2024.05.17.08.27.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 May 2024 08:27:40 -0700 (PDT) Message-ID: Date: Fri, 17 May 2024 17:27:39 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86/kvm/tdx: Save %rbp in TDX_MODULE_CALL To: Dave Hansen , "Kirill A. Shutemov" Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-coco@lists.linux.dev, Dave Hansen , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" References: <20240517121450.20420-1-jgross@suse.com> <2a2guben2ysyeb43rzg6zelzpa57o24ufai3mi6ocewwvgu63l@c7dle47q7hzw> <03d27b6a-be96-44d7-b4ea-aa00ccab4cc5@suse.com> Content-Language: en-US From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 17.05.24 17:16, Dave Hansen wrote: > On 5/17/24 07:44, Juergen Gross wrote: >> Just another data point: Before using this machine I was testing on >> another one with older firmware. That one really didn't support NOM_RBP_MOD >> and I needed to build the kernel with CONFIG_FRAME_POINTER enabled to get >> past the check you are mentioning above. > > For all intents and purposes, the modules that intentionally clobber RBP > don't support Linux. If buggy modules are accidentally clobbering RBP, > we can debate how much the kernel should bend over to accommodate them, > but my preference would be to ignore them. > > I'd much rather put a deny list in the kernel than try to tolerate RBP > clobbering universally. Would you be fine with adding a new X86_FEATURE (or BUG?) allowing to switch RBP save/restore via ALTERNATIVE, controlled by a command line option? Or maybe by adding a new CONFIG_TDX_MODULE_CAN_CLOBBER_RBP (probably using a shorter name) option? TBH I'm slightly puzzled that the firmware I'm using could make it outside Intel. I'm fearing this might happen again. Juergen