From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 E792E3D74 for ; Mon, 21 Nov 2022 12:45:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 37873C433D6; Mon, 21 Nov 2022 12:45:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1669034726; bh=24DMrwR0a4dLCe//QZ6tZ9OUFxGjypwrUBKsHmiGRaU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tdEki5E5Xkw9mLzs8A45hDi6ijcOJeln4dzG56g89YiOgLdcPtXQtRQPP8btsDhEV 2a0upS3pOCEiJ96ogoQr6qhAE8bFPEWMJIFEF2PqGMdeK7ZDXzneQpq7R7TlMULYP9 qSmEWQg8u+Bad+YQnWGmtQw6MLlQHlZpwj7xbO7U= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Pawan Gupta , "Peter Zijlstra (Intel)" , Thadeu Lima de Souza Cascardo , Suleiman Souhlal Subject: [PATCH 4.19 33/34] x86/bugs: Warn when "ibrs" mitigation is selected on Enhanced IBRS parts Date: Mon, 21 Nov 2022 13:43:55 +0100 Message-Id: <20221121124152.084232906@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221121124150.886779344@linuxfoundation.org> References: <20221121124150.886779344@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Pawan Gupta commit eb23b5ef9131e6d65011de349a4d25ef1b3d4314 upstream. IBRS mitigation for spectre_v2 forces write to MSR_IA32_SPEC_CTRL at every kernel entry/exit. On Enhanced IBRS parts setting MSR_IA32_SPEC_CTRL[IBRS] only once at boot is sufficient. MSR writes at every kernel entry/exit incur unnecessary performance loss. When Enhanced IBRS feature is present, print a warning about this unnecessary performance loss. Signed-off-by: Pawan Gupta Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Thadeu Lima de Souza Cascardo Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/2a5eaf54583c2bfe0edc4fea64006656256cca17.1657814857.git.pawan.kumar.gupta@linux.intel.com Signed-off-by: Thadeu Lima de Souza Cascardo Signed-off-by: Suleiman Souhlal Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/bugs.c | 3 +++ 1 file changed, 3 insertions(+) --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -851,6 +851,7 @@ static inline const char *spectre_v2_mod #define SPECTRE_V2_LFENCE_MSG "WARNING: LFENCE mitigation is not recommended for this CPU, data leaks possible!\n" #define SPECTRE_V2_EIBRS_EBPF_MSG "WARNING: Unprivileged eBPF is enabled with eIBRS on, data leaks possible via Spectre v2 BHB attacks!\n" #define SPECTRE_V2_EIBRS_LFENCE_EBPF_SMT_MSG "WARNING: Unprivileged eBPF is enabled with eIBRS+LFENCE mitigation and SMT, data leaks possible via Spectre v2 BHB attacks!\n" +#define SPECTRE_V2_IBRS_PERF_MSG "WARNING: IBRS mitigation selected on Enhanced IBRS CPU, this may cause unnecessary performance loss\n" #ifdef CONFIG_BPF_SYSCALL void unpriv_ebpf_notify(int new_state) @@ -1277,6 +1278,8 @@ static void __init spectre_v2_select_mit case SPECTRE_V2_IBRS: setup_force_cpu_cap(X86_FEATURE_KERNEL_IBRS); + if (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) + pr_warn(SPECTRE_V2_IBRS_PERF_MSG); break; case SPECTRE_V2_LFENCE: