From nobody Sat Dec 27 10:57:24 2025 Received: from mgamail.intel.com (mgamail.intel.com [134.134.136.24]) (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 DC12658ACC; Thu, 21 Dec 2023 09:03:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="Lsf0h+lX" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1703149438; x=1734685438; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=lMZtS6Uq1+UmjnNud65lP8wqI6nTT04uC10gnZ4fF20=; b=Lsf0h+lX9MNfCjhhCF29NtXP9vd4NX+ihu+Qwrvpu58lOxwCbnI6BTEC /IVRSwLBkeaaYwbEEhn8uUInpKEeAPrhBf2/THZsdu1fgckvfRVtyPabe 0N001IWZtp0ha96TTdmWIhmpQh9a3TGuwuAoQ9csmpMi+nr7gE+MzGcuF z6wRnpxCzJ39xkXpYpxV3DmDLqR6kM/jM7luv1F+AqX8xy53zOhhzRRSk 5v6MceHNDWWGmE1xTgXsVzpQdWAT/JSEoHUQMYFTYuff6YJJh1Gh0IZJ4 HhrLyJ5KVq9UfYKh11q1qU76LJVoe3er7ABIqKUgRZSSJed68hT1RsBwU A==; X-IronPort-AV: E=McAfee;i="6600,9927,10930"; a="398729740" X-IronPort-AV: E=Sophos;i="6.04,293,1695711600"; d="scan'208";a="398729740" Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Dec 2023 01:03:48 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10930"; a="900028641" X-IronPort-AV: E=Sophos;i="6.04,293,1695711600"; d="scan'208";a="900028641" Received: from 984fee00a5ca.jf.intel.com (HELO embargo.jf.intel.com) ([10.165.9.183]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Dec 2023 01:03:11 -0800 From: Yang Weijiang To: seanjc@google.com, pbonzini@redhat.com, dave.hansen@intel.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: peterz@infradead.org, chao.gao@intel.com, rick.p.edgecombe@intel.com, mlevitsk@redhat.com, john.allen@amd.com, weijiang.yang@intel.com Subject: [PATCH v8 23/26] KVM: VMX: Set host constant supervisor states to VMCS fields Date: Thu, 21 Dec 2023 09:02:36 -0500 Message-Id: <20231221140239.4349-24-weijiang.yang@intel.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20231221140239.4349-1-weijiang.yang@intel.com> References: <20231221140239.4349-1-weijiang.yang@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Save constant values to HOST_{S_CET,SSP,INTR_SSP_TABLE} field explicitly. Kernel IBT is supported and the setting in MSR_IA32_S_CET is static after post-boot(The exception is BIOS call case but vCPU thread never across it) and KVM doesn't need to refresh HOST_S_CET field before every VM-Enter/ VM-Exit sequence. Host supervisor shadow stack is not enabled now and SSP is not accessible to kernel mode, thus it's safe to set host IA32_INT_SSP_TAB/SSP VMCS field to 0s. When shadow stack is enabled for CPL3, SSP is reloaded from PL3_SSP before it exits to userspace. Check SDM Vol 2A/B Chapter 3/4 for SYSCALL/ SYSRET/SYSENTER SYSEXIT/RDSSP/CALL etc. Prevent KVM module loading if host supervisor shadow stack SHSTK_EN is set in MSR_IA32_S_CET as KVM cannot co-exit with it correctly. Suggested-by: Sean Christopherson Suggested-by: Chao Gao Signed-off-by: Yang Weijiang Reviewed-by: Maxim Levitsky --- arch/x86/kvm/vmx/capabilities.h | 4 ++++ arch/x86/kvm/vmx/vmx.c | 15 +++++++++++++++ arch/x86/kvm/x86.c | 14 ++++++++++++++ arch/x86/kvm/x86.h | 1 + 4 files changed, 34 insertions(+) diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilitie= s.h index 41a4533f9989..ee8938818c8a 100644 --- a/arch/x86/kvm/vmx/capabilities.h +++ b/arch/x86/kvm/vmx/capabilities.h @@ -106,6 +106,10 @@ static inline bool cpu_has_load_perf_global_ctrl(void) return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL; } =20 +static inline bool cpu_has_load_cet_ctrl(void) +{ + return (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_CET_STATE); +} static inline bool cpu_has_vmx_mpx(void) { return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_BNDCFGS; diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 08058b182893..e9c0b571b3bb 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -4371,6 +4371,21 @@ void vmx_set_constant_host_state(struct vcpu_vmx *vm= x) =20 if (cpu_has_load_ia32_efer()) vmcs_write64(HOST_IA32_EFER, host_efer); + + /* + * Supervisor shadow stack is not enabled on host side, i.e., + * host IA32_S_CET.SHSTK_EN bit is guaranteed to 0 now, per SDM + * description(RDSSP instruction), SSP is not readable in CPL0, + * so resetting the two registers to 0s at VM-Exit does no harm + * to kernel execution. When execution flow exits to userspace, + * SSP is reloaded from IA32_PL3_SSP. Check SDM Vol.2A/B Chapter + * 3 and 4 for details. + */ + if (cpu_has_load_cet_ctrl()) { + vmcs_writel(HOST_S_CET, host_s_cet); + vmcs_writel(HOST_SSP, 0); + vmcs_writel(HOST_INTR_SSP_TABLE, 0); + } } =20 void set_cr4_guest_host_mask(struct vcpu_vmx *vmx) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index cf0f9e4474a4..9596763fae8d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -114,6 +114,8 @@ static u64 __read_mostly efer_reserved_bits =3D ~((u64)= EFER_SCE); #endif =20 static u64 __read_mostly cr4_reserved_bits =3D CR4_RESERVED_BITS; +u64 __read_mostly host_s_cet; +EXPORT_SYMBOL_GPL(host_s_cet); =20 #define KVM_EXIT_HYPERCALL_VALID_MASK (1 << KVM_HC_MAP_GPA_RANGE) =20 @@ -9840,6 +9842,18 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init= _ops *ops) return -EIO; } =20 + if (boot_cpu_has(X86_FEATURE_SHSTK)) { + rdmsrl(MSR_IA32_S_CET, host_s_cet); + /* + * Linux doesn't yet support supervisor shadow stacks (SSS), so + * KVM doesn't save/restore the associated MSRs, i.e. KVM may + * clobber the host values. Yell and refuse to load if SSS is + * unexpectedly enabled, e.g. to avoid crashing the host. + */ + if (WARN_ON_ONCE(host_s_cet & CET_SHSTK_EN)) + return -EIO; + } + x86_emulator_cache =3D kvm_alloc_emulator_cache(); if (!x86_emulator_cache) { pr_err("failed to allocate cache for x86 emulator\n"); diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index 9c19dfb5011d..656107e64c93 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -325,6 +325,7 @@ fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vc= pu *vcpu); extern u64 host_xcr0; extern u64 host_xss; extern u64 host_arch_capabilities; +extern u64 host_s_cet; =20 extern struct kvm_caps kvm_caps; =20 --=20 2.39.3