From nobody Sat Feb 7 08:23:02 2026 Received: from mail-pg1-f202.google.com (mail-pg1-f202.google.com [209.85.215.202]) (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 C62AE2D8393 for ; Fri, 23 Jan 2026 22:15:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.202 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769206550; cv=none; b=F+oLcVL8FFVR4qWE7f46mmjePzjDYQ8G/Pu1ip+6V7CQny7Wt4wgtJbmLmmqiHPuUT4l2jYNvEHqMsxCRq3kg8mOjj3yT8J08vA4RXYc/kuMhDqEptmBFMmEHtehLLsj3upbLhLmbB3AsggyA+9/NYNRErJCjpPkNVweToEciFs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769206550; c=relaxed/simple; bh=GcPhUtbSFZCZfML8EMxJfn4YTnBjv127XlcIPdiHxu4=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Qucy5WaV/4vNItbwlMBP1xZ0J1HnEpdFzeYzh2Cl21l6c+YOG7GglhrNafSGVQk6NiA95VGuK0nG3i5swztv2Ltw+aJA4cQz1/KVXmN5R1KOqLt0NcQseGCtWYPisUlFl9tsCIAeA1q75qUnmNC9lJqj4iXoPATuramvmXSrhIM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=zbHL5iZd; arc=none smtp.client-ip=209.85.215.202 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--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="zbHL5iZd" Received: by mail-pg1-f202.google.com with SMTP id 41be03b00d2f7-c613929d317so1477954a12.2 for ; Fri, 23 Jan 2026 14:15:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1769206548; x=1769811348; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=CGdd8BKfTwRMHvUG+hG2z6R5W0TDHrveqU9uM1M3OZY=; b=zbHL5iZd3fqHidAh0+LZIy8gpa97f2PNQ/7EluMjVNwPnII6LLn17VDwA2i+Czd5oi HFRHBFVK/P1HKQTm5FP1xcZ8ozSLOd4YRgJLwIquqdgzW057XPBFpgTTLbI51/OT3Umb EIPuIrAGgLyq9TYBgFvdqcxcA3uTUX+5sGo+WRo7cnQmbWsuMIRMJOQ4gxxp/gs3WV+Y xbSMbQdPTUTfFuKXHTWKgnR6HsA6QhMgg0kpbbXUfsriotOfJtZ83bPQt6YC7nZG1yJ7 Ioq9OPAPKHRWwOYWXP5kKyRMLGsS5NmcykGLycuDuwUve/hpgL9XFDC4FMwAYAehvwWl 11xw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1769206548; x=1769811348; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=CGdd8BKfTwRMHvUG+hG2z6R5W0TDHrveqU9uM1M3OZY=; b=lrubNGGLX0tREnHlBn/Qdb044Ez71Wef+qO5JLGnCUgrl2y5v2RoR1JI7VgL5XRFrg //bP4E8ZBME3QkPF/KGACnR4NsYOOj1D/aIAtURYPz0xd9mA0GvzouvFLjee8JOOPigD LgVjhbWqEDS7wIAggqx6p1DHpY0gbtsrJz3j/TTkAK8NHZYt7FQIS2wiT0aw1DJ82Bf/ vC3V9eWopmTgBD6cmROwbCKwM2byd9ykaUrmtJWnugbJotTwNfDSDLW3ijDatqiqNAY0 ouH6uvSfUKzra8r1qGbFD+t67aZYlW1Jhh30U8KC7d4V5rhlviBq8VH0tu4WfJuhm4+y rOLQ== X-Forwarded-Encrypted: i=1; AJvYcCV1+I65h2s5UghL7JOfTha3sO/MEjX5+DR59ghmbDGbrMWWsQnbXpUd8viO/Ki6wSELV5bbZQQRO3xwVuU=@vger.kernel.org X-Gm-Message-State: AOJu0YzaQEehi3gnAvpftESALfQtH90eKyoh8ZrFQGKWxBrKzTlA9UCi G/EmqNxfMdCzC+AuUBPjpr32G8tFc1pPnEWFu4/CbyNymkMklY9PREt5FRK/dFohNxt29cFVVO9 KkofV1A== X-Received: from pgct22.prod.google.com ([2002:a05:6a02:5296:b0:c63:3c6b:9ab6]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:7284:b0:38d:f80d:1bc0 with SMTP id adf61e73a8af0-38e6f7f1025mr4952983637.55.1769206548098; Fri, 23 Jan 2026 14:15:48 -0800 (PST) Reply-To: Sean Christopherson Date: Fri, 23 Jan 2026 14:15:41 -0800 In-Reply-To: <20260123221542.2498217-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260123221542.2498217-1-seanjc@google.com> X-Mailer: git-send-email 2.52.0.457.g6b5491de43-goog Message-ID: <20260123221542.2498217-3-seanjc@google.com> Subject: [PATCH 2/3] KVM: x86: Harden against unexpected adjustments to kvm_cpu_caps From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Mathias Krause , John Allen , Rick Edgecombe , Chao Gao , Binbin Wu , Xiaoyao Li , Jim Mattson Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Add a flag to track when KVM is actively configuring its CPU caps, and WARN if a cap is set or cleared if KVM isn't in its configuration stage. Modifying CPU caps after {svm,vmx}_set_cpu_caps() can be fatal to KVM, as vendor setup code expects the CPU caps to be frozen at that point, e.g. will do additional configuration based on the caps. Signed-off-by: Sean Christopherson Reviewed-by: Chao Gao --- arch/x86/kvm/cpuid.c | 8 ++++++++ arch/x86/kvm/cpuid.h | 4 ++++ 2 files changed, 12 insertions(+) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 267e59b405c1..2f01511135c2 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -36,6 +36,9 @@ u32 kvm_cpu_caps[NR_KVM_CPU_CAPS] __read_mostly; EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_cpu_caps); =20 +bool kvm_is_configuring_cpu_caps __read_mostly; +EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_is_configuring_cpu_caps); + struct cpuid_xstate_sizes { u32 eax; u32 ebx; @@ -830,6 +833,9 @@ void kvm_initialize_cpu_caps(void) { memset(kvm_cpu_caps, 0, sizeof(kvm_cpu_caps)); =20 + WARN_ON_ONCE(kvm_is_configuring_cpu_caps); + kvm_is_configuring_cpu_caps =3D true; + BUILD_BUG_ON(sizeof(kvm_cpu_caps) - (NKVMCAPINTS * sizeof(*kvm_cpu_caps))= > sizeof(boot_cpu_data.x86_capability)); =20 @@ -1305,6 +1311,8 @@ void kvm_finalize_cpu_caps(void) kvm_cpu_cap_clear(X86_FEATURE_IBT); kvm_caps.supported_xss &=3D ~XFEATURE_MASK_CET_ALL; } + + kvm_is_configuring_cpu_caps =3D false; } EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_finalize_cpu_caps); =20 diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h index 3b0b4b1adb97..07175dff24d6 100644 --- a/arch/x86/kvm/cpuid.h +++ b/arch/x86/kvm/cpuid.h @@ -8,6 +8,8 @@ #include =20 extern u32 kvm_cpu_caps[NR_KVM_CPU_CAPS] __read_mostly; +extern bool kvm_is_configuring_cpu_caps __read_mostly; + void kvm_initialize_cpu_caps(void); void kvm_finalize_cpu_caps(void); =20 @@ -189,6 +191,7 @@ static __always_inline void kvm_cpu_cap_clear(unsigned = int x86_feature) { unsigned int x86_leaf =3D __feature_leaf(x86_feature); =20 + WARN_ON_ONCE(!kvm_is_configuring_cpu_caps); kvm_cpu_caps[x86_leaf] &=3D ~__feature_bit(x86_feature); } =20 @@ -196,6 +199,7 @@ static __always_inline void kvm_cpu_cap_set(unsigned in= t x86_feature) { unsigned int x86_leaf =3D __feature_leaf(x86_feature); =20 + WARN_ON_ONCE(!kvm_is_configuring_cpu_caps); kvm_cpu_caps[x86_leaf] |=3D __feature_bit(x86_feature); } =20 --=20 2.52.0.457.g6b5491de43-goog