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X-CSE-ConnectionGUID: UyneHoKtQjusMm0MnPp++w== X-CSE-MsgGUID: GKc+VJLvRVaLOKMNLRdCzw== X-IronPort-AV: E=McAfee;i="6800,10657,11456"; a="68821241" X-IronPort-AV: E=Sophos;i="6.16,215,1744095600"; d="scan'208";a="68821241" Received: from orviesa002.jf.intel.com ([10.64.159.142]) by orvoesa102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Jun 2025 08:58:21 -0700 X-CSE-ConnectionGUID: 1M6ojOgnSJ223/q1IXO8ng== X-CSE-MsgGUID: OSpIJxdjTMaQi4oha9s2dQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,215,1744095600"; d="scan'208";a="176811066" Received: from iherna2-mobl4.amr.corp.intel.com (HELO [10.125.111.31]) ([10.125.111.31]) by orviesa002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Jun 2025 08:58:20 -0700 Message-ID: Date: Fri, 6 Jun 2025 08:58:18 -0700 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 v3] x86/virt/tdx: Enforce no indirect calls of TDX assembly To: Kai Huang , peterz@infradead.org, tglx@linutronix.de, bp@alien8.de, mingo@redhat.com, hpa@zytor.com, kirill.shutemov@linux.intel.com Cc: rick.p.edgecombe@intel.com, x86@kernel.org, samitolvanen@google.com, linux-kernel@vger.kernel.org References: <20250606130737.30713-1-kai.huang@intel.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit It doesn't really "enforce" anything. But, oh well, I'll just fix it up when I apply it early next week. Here's what I'll probably apply: x86/virt/tdx: Avoid indirect calls to TDX assembly functions Two 'static inline' TDX helper functions (sc_retry() and sc_retry_prerr()) take function pointer arguments which refer to assembly functions. Normally, the compiler inlines the TDX helper, realizes that the function pointer targets are completely static -- thus can be resolved at compile time -- and generates direct call instructions. But, other times (like when CONFIG_CC_OPTIMIZE_FOR_SIZE=y), the compiler declines to inline the helpers and will instead generate indirect call instructions. Indirect calls to assembly functions require special annotation (for various Control Flow Integrity mechanisms). But TDX assembly functions lack the special annotations and can only be called directly. Annotate both the helpers as '__always_inline' to prod the compiler into maintaining the direct calls. There is no guarantee here, but Peter has volunteered to report the compiler bug if this assumption ever breaks[1]. ... > This was found through randconfig testing, presumably setting > CONFIG_CC_OPTIMIZE_FOR_SIZE=1 when objtool spewed a bunch of these: > > vmlinux.o: warning: objtool: tdh_mem_range_block+0x7e: relocation to > !ENDBR: __seamcall_ret+0x0 > > Link: https://lore.kernel.org/lkml/20250605145914.GW39944@noisy.programming.kicks-ass.net/ [1]