From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f74.google.com (mail-wr1-f74.google.com [209.85.221.74]) (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 791DF3597F for ; Fri, 21 Feb 2025 14:31:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740148265; cv=none; b=WcqIJ3SqYhU0FaCNFxxjmnnsXYEeba7J4Y3lkWMbgzQZFPGK5CVxylj2fWDMT6JoTZvVWi0y28tHREdkCLhcONTUg3IAtbGPcUlNUrwcjPQcoDWfqlNUTq8zU65C3VJke6a0vSLOWmahODpHXKNN3koI4KnGWIf9LQpBknVm0Hc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740148265; c=relaxed/simple; bh=OXOS/+rmht491HT7vYQuTBtWV+4wAVuMUGedjiWsvoM=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=nUry8Mj9whzc59S7VqtOJDDCBq8vwI+ScAcMkM7fHzBhpKsPWXVXWKtZs5NI6xmSQla3gWMn647Hcj31UVEohJlyOPhqLFqyHkar7N3X0UBzxuoXajNRWd0AisSY5fEbHfOiv/qkdTUozP71q6pX6qZtNUB8PfIqOyXdHewqUuU= 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=sDkykc0X; arc=none smtp.client-ip=209.85.221.74 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="sDkykc0X" Received: by mail-wr1-f74.google.com with SMTP id ffacd0b85a97d-38f27acb979so2816530f8f.0 for ; Fri, 21 Feb 2025 06:31:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1740148262; x=1740753062; darn=lists.linux.dev; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=d6lHGB4RW+fUm+w8DCgpzh+6Wzc49VTdZcnDOzB17rM=; b=sDkykc0XdJ4tzaGnlNdi/8VcruXKQU0HF+sIHtCQjGoaiQYZvoCl0562zVInXVs9rY mAq/VT2er/7ZHX4Y8yTWFrpwL0wOwU48deMKMgq5O1kU9RQX6YnczBKJFnzimXpzsS9X y2PKHQa4uc1dvC73yDNScsgtg/1tk2s7GSD1FFSToDMLhFExk+hmy1eMj4ZyffY8Dps8 Jk55Fyh6Anj5NPID391RPJDObJlMaYSBpOdTlf5yT1wyjJBbFsmIcuppnAVOQUnYXIiM MLUkfEQ3AU4TnrEXZuYAeG+AiOL2okSFUNJ+o870XC7HxAh935VDv9nihiGGvy4IkXrZ mHdw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1740148262; x=1740753062; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=d6lHGB4RW+fUm+w8DCgpzh+6Wzc49VTdZcnDOzB17rM=; b=JWp+FEvThUMjGhvRMeZME8a1jW4oO+HiuKb1FeSoU6KP80k6ivWtlyYfYFHFi7EXWQ C0zgqQvLr5aEHyt8fiE5ItdLfIT6D/K92fn4k1ucB+iYM32M77jOKNSeeNtQFZV/Fftm XIersOZCs4tNWxX830klQWRKZ1M1KEdaTyRsKJ7xoMbUYR41naaxtZzHoVryK4LdBaLm uxmYnT2Ifk5IRWhi4wvq7Q/KygN/RPwX0KA/s8pGGIPahWmWRR3TMqeje7Ln3cEjLxN9 qafRUGRpRmMFxqFnyrCgCWlLqThlPwvCQHTmvGgCZXIkhtAPnUOVWwgGqnyfNJq+YAiB zDUQ== X-Gm-Message-State: AOJu0YxB4J9CvZEKyK2vD+cwjLqB/H22UbB710r9k3s0l+jS5DcRplAC 9d6yxP+Ewpzxloke9IERzI80310ocUmHZ2D/tns4t+nGcOXfcPucr/NGvOMoqkYt/nJIlqmAx5W obPdgPfirbQ== X-Google-Smtp-Source: AGHT+IHp9KpPqihhkAMCoq7AJPuOMZlSKfO7K/P7TqXNdVLdlMAnTqXOd4eugadlp0OBHoJR/g4/4JhJ/pRKdA== X-Received: from wmsp4.prod.google.com ([2002:a05:600c:1d84:b0:439:942c:b180]) (user=derkling job=prod-delivery.src-stubby-dispatcher) by 2002:a5d:6da5:0:b0:38d:cf33:31a1 with SMTP id ffacd0b85a97d-38f707afc79mr2963941f8f.23.1740148261904; Fri, 21 Feb 2025 06:31:01 -0800 (PST) Date: Fri, 21 Feb 2025 14:30:51 +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: <20250221143051.23140-1-derkling@google.com> Subject: [PATCH 6.1] 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 49cea5b81649d..ca8dd7e5585f0 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2506,7 +2506,8 @@ 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 fa2045ad408a7..03221a060ae77 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1092,6 +1092,8 @@ 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 @@ -1101,8 +1103,6 @@ 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, @@ -2607,6 +2607,7 @@ 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; /* @@ -2616,6 +2617,13 @@ 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"); @@ -2624,8 +2632,8 @@ 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; @@ -2637,9 +2645,9 @@ 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