From nobody Fri Dec 19 14:33:59 2025 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (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 5865825771 for ; Thu, 6 Nov 2025 01:13:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762391615; cv=none; b=S4vE7QUJuWPaH9FDdUtCvhEkX0KV51XglHiavUq8HV+dIlIXIghGllx7R5tJb3nZD140Hj5Y9duyZMF6pOzGtn8XOUHEXWpd2g/A0X2cWe+J/eYT7p73joMreQqGRDz0zioV6ZxtCcdeTc9uB82/efZwJFFjVtlPwRuzqAIJSW4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762391615; c=relaxed/simple; bh=80Wiat1QmCZkX5CwNMua5eaZtZ21PjI7recyDsW8I40=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=Timssz8y9xmxc4WSuJDGlYh1owg5Xez7ZDrGeB+LrB5v932BgrGzkUfOul2fpjAcAE0sHLDaCmg/FrTQTOaYzoryfdKlAe17/m9+Q2rzyiVYnmVNgq2GVwYWYZYbRBEvwXWuIe8oPMoEcDE5gViYgcNRN7OaRDpUIoAfvwpf810= 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=ohRlIWGs; arc=none smtp.client-ip=209.85.214.201 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="ohRlIWGs" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-272b7bdf41fso7062115ad.0 for ; Wed, 05 Nov 2025 17:13:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1762391614; x=1762996414; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:reply-to:from:to:cc :subject:date:message-id:reply-to; bh=VqKp0CwGeQO+vX6lyD3ithXWPZSPW6/801NskRBS3pw=; b=ohRlIWGsD8UHC0TfcA8CecUoXLJRfDqXpqQbcw8VLYF869RQNVityCld8eXZR9Qybr hFELxEYK06UYB2xTcztzQXNRz/VkYzdxe4dE3A0DVSJQAv3NyBkZ4z0sf1PC2g9RskQK wi0mFs+xBOenfnb9lp09hY4mV8oiLrVowPiz2ezbFmRO2KiDHbiTJNZDi7hP+08sq1f/ JpyL8jVN1zdzXIm/dhmqr69LhRhBTlgOW9ZL7+Q+8vz28HbYh3Ejbdloyr3yUVFfQQPI hyw4ovb+oNfs+jqVy7uCx1YQDE6WKjrTaobUTsLUO8tERoGs5OIkTZq0xzZbtDLsLRuH PWNg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1762391614; x=1762996414; h=cc:to:from:subject:message-id:mime-version:date:reply-to :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=VqKp0CwGeQO+vX6lyD3ithXWPZSPW6/801NskRBS3pw=; b=YGmcJ+gUWExQU1ahTMSlp7db1Kqgmi1CMzwTwpqAUMDRyoyEhs/0X2EVv1Al4zTT29 oC198Ntnto2GBkDkR/sx37c3Xihvkx2GF2McqXkdLaGDqgU4oQMEDMJq1HlUXzG49+74 9KIB4YrMTTBfvUjS1KPERB6AXVIAEcag6eV0X3xfhIUHdIRnNTwas3+3640jRlevvKQm 7eK7dO7XZGkgT5fRMBFqiNS7gpQVyga4UEgGdL9X2H/m6ZHfxmL23MhYoYIK3lUeaBKJ eLboVtNpslz4jYAyKRZ5ffbr7O60N9Ld3kRhmrRJCPMsYA4Rdhal/OTAOMVH0aqfkL70 rApw== X-Forwarded-Encrypted: i=1; AJvYcCVK5Mb4Q+zI5LedJnhY0123GWdRYgpa3IO/pcsZ9w8v22/IzBlpOxY0+UP9z3TVNaTvsBIWkK3ulIwFcf8=@vger.kernel.org X-Gm-Message-State: AOJu0YwfNOGqrve1knMzWfkU251RgELNk4CKOPBswSPYggu5uzorAP+m dYp0Y+D9+7YN/vvBumg+8AyLrSmZ+bToX/or9kauwAJyZrUI2tIaMq6iTuWGFc4WaWqpcJ1ri4o 6o9RNvQ== X-Google-Smtp-Source: AGHT+IGZcQoqqRr+4WmRuSJjj17n9/E5KkIA14kwU5ltSuF7hBvooIAUFHJHZmSE4bAa5nn44H0/G6OGRqY= X-Received: from plrd7.prod.google.com ([2002:a17:902:aa87:b0:295:70a9:9091]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:da8c:b0:295:5948:f5d8 with SMTP id d9443c01a7336-2962adb0f2fmr71425915ad.48.1762391613676; Wed, 05 Nov 2025 17:13:33 -0800 (PST) Reply-To: Sean Christopherson Date: Wed, 5 Nov 2025 17:13:30 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.51.2.1041.gc1ab5b90ca-goog Message-ID: <20251106011330.75571-1-seanjc@google.com> Subject: [PATCH] KVM: SVM: Ensure SPEC_CTRL[63:32] is context switched between guest and host From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Uros Bizjak Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Uros Bizjak SPEC_CTRL is an MSR, i.e. a 64-bit value, but the VMRUN assembly code assumes bits 63:32 are always zero. The bug is _currently_ benign because neither KVM nor the kernel support setting any of bits 63:32, but it's still a bug that needs to be fixed. Signed-off-by: Uros Bizjak Suggested-by: Sean Christopherson Co-developed-by: Sean Christopherson Signed-off-by: Sean Christopherson --- arch/x86/kvm/svm/vmenter.S | 44 +++++++++++++++++++++++++++++++------- 1 file changed, 36 insertions(+), 8 deletions(-) diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S index 235c4af6b692..53f45f5b611f 100644 --- a/arch/x86/kvm/svm/vmenter.S +++ b/arch/x86/kvm/svm/vmenter.S @@ -52,11 +52,23 @@ * there must not be any returns or indirect branches between this code * and vmentry. */ - movl SVM_spec_ctrl(%_ASM_DI), %eax - cmp PER_CPU_VAR(x86_spec_ctrl_current), %eax +#ifdef CONFIG_X86_64 + mov SVM_spec_ctrl(%rdi), %rdx + cmp PER_CPU_VAR(x86_spec_ctrl_current), %rdx je 801b + movl %edx, %eax + shr $32, %rdx +#else + mov SVM_spec_ctrl(%edi), %eax + mov PER_CPU_VAR(x86_spec_ctrl_current), %ecx + xor %eax, %ecx + mov SVM_spec_ctrl + 4(%edi), %edx + mov PER_CPU_VAR(x86_spec_ctrl_current + 4), %esi + xor %edx, %esi + or %esi, %ecx + je 801b +#endif mov $MSR_IA32_SPEC_CTRL, %ecx - xor %edx, %edx wrmsr jmp 801b .endm @@ -81,13 +93,26 @@ jnz 998f rdmsr movl %eax, SVM_spec_ctrl(%_ASM_DI) + movl %edx, SVM_spec_ctrl + 4(%_ASM_DI) 998: - /* Now restore the host value of the MSR if different from the guest's. = */ - movl PER_CPU_VAR(x86_spec_ctrl_current), %eax - cmp SVM_spec_ctrl(%_ASM_DI), %eax +#ifdef CONFIG_X86_64 + mov SVM_spec_ctrl(%rdi), %rdx + cmp PER_CPU_VAR(x86_spec_ctrl_current), %rdx je 901b - xor %edx, %edx + mov PER_CPU_VAR(x86_spec_ctrl_current), %rdx + movl %edx, %eax + shr $32, %rdx +#else + mov SVM_spec_ctrl(%edi), %esi + mov PER_CPU_VAR(x86_spec_ctrl_current), %eax + xor %eax, %esi + mov SVM_spec_ctrl + 4(%edi), %edi + mov PER_CPU_VAR(x86_spec_ctrl_current + 4), %edx + xor %edx, %edi + or %edi, %esi + je 901b +#endif wrmsr jmp 901b .endm @@ -211,7 +236,10 @@ SYM_FUNC_START(__svm_vcpu_run) /* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */ FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT =20 - /* Clobbers RAX, RCX, RDX. */ + /* + * Clobbers RAX, RCX, RDX (and EDI on 32-bit), consumes RDI (@svm) and + * RSP (pointer to @spec_ctrl_intercepted). + */ RESTORE_HOST_SPEC_CTRL =20 /* base-commit: a996dd2a5e1ec54dcf7d7b93915ea3f97e14e68a --=20 2.51.2.1041.gc1ab5b90ca-goog