From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f73.google.com (mail-wm1-f73.google.com [209.85.128.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7960420E6E6 for ; Fri, 21 Feb 2025 14:52:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740149559; cv=none; b=g9+l9WHd9X+tUDucNvy27nky5MqduajMMY5g6uzgEx7dMRNlHbxAIG/Fms777fmLwawUqGlQxl9JC6cIQeYi3rfJe6goZf5BRmIREACj9PXWucRcoaXk0Rxm/q0N3bbavcQbeGX4Es4aY62e0ex0NJs6RDSK6QUIQKUm341eJLc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740149559; c=relaxed/simple; bh=VWMhrPMtisJb4hIm7Q7em7/129wWiVmvlzMbHR8p3mI=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=LmrL52Ois/aUnSYBUu1TLXM7v36WHm0Wlm4cQ7xPorgECkIWQbq/tu7SvlwyOAzbHCSI2adNsz+VAhEmuec/nC5KdsNZ3UxzYJmlXe7/2yn2xcWcMGX1E3tjJjdgxjQKKqpQf1jZ2BNu1hfwXOV7DwqYsgbFDNaWLMbY6GgQf9k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--derkling.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=LiWj8y0t; arc=none smtp.client-ip=209.85.128.73 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--derkling.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="LiWj8y0t" Received: by mail-wm1-f73.google.com with SMTP id 5b1f17b1804b1-4399a5afc95so10310345e9.3 for ; Fri, 21 Feb 2025 06:52:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1740149556; x=1740754356; darn=lists.linux.dev; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=PJklh7u9DqRRvWHRSedTQSVAJYR9DI+wbKJuVOJ/zZU=; b=LiWj8y0tvJhKN8Ll3JxLgOdxYJ7I2Tt6yutYRnzpLZmP4SByTBpZSu83pXCiVj05I4 PxB5GH4G7YnPV+402vsiGku06uYHVOtQneEUqdioFB0XUcbb3Yb0db5yirccCmzKhnnW 3AqveJJ8RxtQnWI8je2lVQy+z0mqJnG8uxAEjZ2RZk147cuQ6psOfpabblybxj07h4OD x8008zST7A7lTLXovvho41bEkpdjR0QLKzBJ3tPczLMM8RS9N7v4Lo4aEleTPpi6rQmt W7r+4UAtvPyOtz9VOFKIDlAm2yHWBh819Met1xOFNeUriVqEPnqFw03yEO8j9J90KjmC 7J7A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1740149556; x=1740754356; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=PJklh7u9DqRRvWHRSedTQSVAJYR9DI+wbKJuVOJ/zZU=; b=I6+Jl2qIwnn1XMr+Rgota8vEf2xYzqTU7qfcrOSl33HcHVgj+tP9n1xGuPFRvVaQuk K0KzazBlie01ll9UZojIYjtTxgojQReAUOKBc5H5j+yEgkH8r6Xdbn4h51aSeFNx5F1J KbMc3QJmtJ4eqLFwV9fhFUX7aY/bP4vspXiuSorfSHQGx5om+FoxFqecoAhjpDCs2Pwn u3MZUg6zgHs7iZs+HErVa3b5ieJyM2Jje4S56RHi3Oe0o2e9uWFV66CM3k85oyRJYeZN QqvNNqpJtufdJKoNKnn7U8xY/Ad795mnncSBQfBygF77zbEM15757mty1msBYGyxQ1PI uJeQ== X-Gm-Message-State: AOJu0YwYdBZE6KrBZv4FrcC9f5vuRd8nM3qCFdRqTWx0PlYy0At/zh1o bCPk8JYCPSDmADy0nRE0zFIQhgs6tqotml86rEFENPGvml9CLNIxW7f9M2pwPU2+ivOUms8L8WM ejEjkrgkVKw== X-Google-Smtp-Source: AGHT+IEwZvTcD91+iLHw+VrVG2ux5qKn48gbc83ImXS9beNu4zdCBswbeRoOKzBIt4Xn/WEPEMWSlmskee/ysg== X-Received: from wmbfk14.prod.google.com ([2002:a05:600c:cce:b0:439:7d73:d8fc]) (user=derkling job=prod-delivery.src-stubby-dispatcher) by 2002:a5d:6d0a:0:b0:38d:dd70:d70d with SMTP id ffacd0b85a97d-38f6e947399mr3767006f8f.18.1740149555851; Fri, 21 Feb 2025 06:52:35 -0800 (PST) Date: Fri, 21 Feb 2025 14:51:56 +0000 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog Message-ID: <20250221145156.195014-1-derkling@google.com> Subject: [PATCH 5.10] x86/cpu/kvm: SRSO: Fix possible missing IBPB on VM-Exit From: Patrick Bellasi To: stable@vger.kernel.org Cc: patches@lists.linux.dev, Borislav Petkov , Patrick Bellasi , Brendan Jackman , Yosry Ahmed Content-Type: text/plain; charset="UTF-8" commit 318e8c339c9a0891c389298bb328ed0762a9935e upstream. In [1] the meaning of the synthetic IBPB flags has been redefined for a better separation of concerns: - ENTRY_IBPB -- issue IBPB on entry only - IBPB_ON_VMEXIT -- issue IBPB on VM-Exit only and the Retbleed mitigations have been updated to match this new semantics. Commit [2] was merged shortly before [1], and their interaction was not handled properly. This resulted in IBPB not being triggered on VM-Exit in all SRSO mitigation configs requesting an IBPB there. Specifically, an IBPB on VM-Exit is triggered only when X86_FEATURE_IBPB_ON_VMEXIT is set. However: - X86_FEATURE_IBPB_ON_VMEXIT is not set for "spec_rstack_overflow=ibpb", because before [1] having X86_FEATURE_ENTRY_IBPB was enough. Hence, an IBPB is triggered on entry but the expected IBPB on VM-exit is not. - X86_FEATURE_IBPB_ON_VMEXIT is not set also when "spec_rstack_overflow=ibpb-vmexit" if X86_FEATURE_ENTRY_IBPB is already set. That's because before [1] this was effectively redundant. Hence, e.g. a "retbleed=ibpb spec_rstack_overflow=bpb-vmexit" config mistakenly reports the machine still vulnerable to SRSO, despite an IBPB being triggered both on entry and VM-Exit, because of the Retbleed selected mitigation config. - UNTRAIN_RET_VM won't still actually do anything unless CONFIG_MITIGATION_IBPB_ENTRY is set. For "spec_rstack_overflow=ibpb", enable IBPB on both entry and VM-Exit and clear X86_FEATURE_RSB_VMEXIT which is made superfluous by X86_FEATURE_IBPB_ON_VMEXIT. This effectively makes this mitigation option similar to the one for 'retbleed=ibpb', thus re-order the code for the RETBLEED_MITIGATION_IBPB option to be less confusing by having all features enabling before the disabling of the not needed ones. For "spec_rstack_overflow=ibpb-vmexit", guard this mitigation setting with CONFIG_MITIGATION_IBPB_ENTRY to ensure UNTRAIN_RET_VM sequence is effectively compiled in. Drop instead the CONFIG_MITIGATION_SRSO guard, since none of the SRSO compile cruft is required in this configuration. Also, check only that the required microcode is present to effectively enabled the IBPB on VM-Exit. Finally, update the KConfig description for CONFIG_MITIGATION_IBPB_ENTRY to list also all SRSO config settings enabled by this guard. Fixes: 864bcaa38ee4 ("x86/cpu/kvm: Provide UNTRAIN_RET_VM") [1] Fixes: d893832d0e1e ("x86/srso: Add IBPB on VMEXIT") [2] Reported-by: Yosry Ahmed Signed-off-by: Patrick Bellasi Reviewed-by: Borislav Petkov (AMD) Cc: stable@kernel.org Signed-off-by: Linus Torvalds --- arch/x86/Kconfig | 3 ++- arch/x86/kernel/cpu/bugs.c | 20 ++++++++++++++------ 2 files changed, 16 insertions(+), 7 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 0c802ade80406..00ae2e2adcadb 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2463,7 +2463,8 @@ config CPU_IBPB_ENTRY depends on CPU_SUP_AMD && X86_64 default y help - Compile the kernel with support for the retbleed=ibpb mitigation. + Compile the kernel with support for the retbleed=ibpb and + spec_rstack_overflow={ibpb,ibpb-vmexit} mitigations. config CPU_IBRS_ENTRY bool "Enable IBRS on kernel entry" diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 0b7f6bcbb8ea9..725f827718a71 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1061,6 +1061,8 @@ static void __init retbleed_select_mitigation(void) case RETBLEED_MITIGATION_IBPB: setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB); + setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT); + mitigate_smt = true; /* * IBPB on entry already obviates the need for @@ -1070,8 +1072,6 @@ static void __init retbleed_select_mitigation(void) setup_clear_cpu_cap(X86_FEATURE_UNRET); setup_clear_cpu_cap(X86_FEATURE_RETHUNK); - mitigate_smt = true; - /* * There is no need for RSB filling: entry_ibpb() ensures * all predictions, including the RSB, are invalidated, @@ -2469,6 +2469,7 @@ static void __init srso_select_mitigation(void) if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) { if (has_microcode) { setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB); + setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT); srso_mitigation = SRSO_MITIGATION_IBPB; /* @@ -2478,6 +2479,13 @@ static void __init srso_select_mitigation(void) */ setup_clear_cpu_cap(X86_FEATURE_UNRET); setup_clear_cpu_cap(X86_FEATURE_RETHUNK); + + /* + * There is no need for RSB filling: entry_ibpb() ensures + * all predictions, including the RSB, are invalidated, + * regardless of IBPB implementation. + */ + setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT); } } else { pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n"); @@ -2486,8 +2494,8 @@ static void __init srso_select_mitigation(void) break; case SRSO_CMD_IBPB_ON_VMEXIT: - if (IS_ENABLED(CONFIG_CPU_SRSO)) { - if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) { + if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) { + if (has_microcode) { setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT); srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT; @@ -2499,9 +2507,9 @@ static void __init srso_select_mitigation(void) setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT); } } else { - pr_err("WARNING: kernel not compiled with CPU_SRSO.\n"); + pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n"); goto pred_cmd; - } + } break; default: -- 2.48.1.601.g30ceb7b040-goog