From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 232D01922FB for ; Tue, 15 Jul 2025 15:35:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752593727; cv=none; b=cntOAKncH8+RX9QlnlCpSHhKGz9oGpglMdZJ4Tw6oxwBbw3Nzl/5gd2770zy07ZZJ5uQVrLD3PlwDxra3GA4SF8QeKIU9C2eydzpgEvQxpkQ+EEqGCiKQhz7WDmy0CHhK9KxIKWHyMYrtNeVTazEg4z3QQ2AEEi2sUBiVw+XTQA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752593727; c=relaxed/simple; bh=1Os82t3UH4xxEkIYAOAU8VzCGx6w1OSDILXxwdCWBQI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=PR9cyAxiCRKY0eSZ3H2gCnEpqbKtYMXtiJM7eIJxFhLfufCDYvSB0LVUWBfiQiwqwe4sQpzwa4t+jkOY+ut1aNRKRxZv1p/DjZ4aJixHXE3S9JQCZAQmZcJL5QVxlwAHZ0Vv90KRkkwq1FW+4tWjAyvBwqt4dTYOc7Zz4gbdJzk= ARC-Authentication-Results:i=1; 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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=E7qVkR2yRzyO9NlR59set1lElucQm0FxobGL7ZKB2qomRXETP6I1XuNyck29IiD4E d6kLC8UShFjSqHi2zwww2DXhef3gVzEMUsUe0RVe6cE0OqsJV4vMMfq4KfmMhBGbXN IEq7AnJYygcE3vJuVCg8l5cRRCV6Bos882QEQAYxJOrE7FL1SrPxxt/hO+NGmsC6dE fq1y6WGWd9+bhCcvRxNj6Tm9+5PIDLsXniy2M8VImkVAkONoVSb8busxtOZ1n25Rsi lXhuwiFopQ+T33zQinE5ZBTjuNIwP2c+4DJkNl5sfb/vSSKbJqxRRWrGMDlA1j8c9f lGQ9lO9tm95dg== Message-ID: <025501f2-5122-44c2-ae20-0cce86e8c426@zytor.com> Date: Tue, 15 Jul 2025 08:34:51 -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 v1 1/1] x86/fred: Remove ENDBR64 from FRED entry points To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, luto@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, jmill@asu.edu, andrew.cooper3@citrix.com References: <20250715064437.807569-1-xin@zytor.com> <20250715084034.GO1613200@noisy.programming.kicks-ass.net> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/15/2025 1:40 AM, Peter Zijlstra wrote: > On Mon, Jul 14, 2025 at 11:50:57PM -0700, Xin Li wrote: >> On 7/14/2025 11:44 PM, Xin Li (Intel) wrote: >>> The FRED specification v9.0 states that there is no need for FRED >>> event handlers to begin with ENDBR64, because in the presence of >>> supervisor indirect branch tracking, FRED event delivery does not >>> enter the WAIT_FOR_ENDBRANCH state. >>> >>> As a result, remove ENDBR64 from FRED entry points. >>> >>> Then add ANNOTATE_NOENDBR to indicate that FRED entry points will >>> never be used for indirect calls to suppress an objtool warning. >>> >>> This change implies that any indirect CALL/JMP to FRED entry points >>> causes #CP in the presence of supervisor indirect branch tracking. >>> >>> Credit goes to Jennifer Miller and other contributors >>> from Arizona State University whose work led to this change. >>> >>> Link:https://lore.kernel.org/linux-hardening/Z60NwR4w%2F28Z7XUa@ubun/ >>> Reviewed-by: H. Peter Anvin (Intel) >>> Signed-off-by: Xin Li (Intel) >>> Cc: Jennifer Miller >>> Cc: Peter Zijlstra >>> Cc: Andrew Cooper >>> Cc: H. Peter Anvin >> Sorry, forgot to put CC stable. > Fixes: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code") > > Right? You bet! Will send v2 to address it soon.