linux-kernel - Re: [PATCH v16 19/51] KVM: x86: Don't emulate task switches when IBT or SHSTK is enabled

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <c93438be-642b-47f1-b4ff-9551b9192471@intel.com>
Date: Tue, 23 Sep 2025 22:16:57 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Binbin Wu <binbin.wu@...ux.intel.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, Tom Lendacky <thomas.lendacky@....com>,
 Mathias Krause <minipli@...ecurity.net>, John Allen <john.allen@....com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>, Chao Gao <chao.gao@...el.com>,
 Maxim Levitsky <mlevitsk@...hat.com>, Zhang Yi Z
 <yi.z.zhang@...ux.intel.com>, Xin Li <xin@...or.com>
Subject: Re: [PATCH v16 19/51] KVM: x86: Don't emulate task switches when IBT
 or SHSTK is enabled

On 9/23/2025 1:23 AM, Sean Christopherson wrote:
> On Mon, Sep 22, 2025, Binbin Wu wrote:
>>
>>
>> On 9/20/2025 6:32 AM, Sean Christopherson wrote:
>>> Exit to userspace with KVM_INTERNAL_ERROR_EMULATION if the guest triggers
>>> task switch emulation with Indirect Branch Tracking or Shadow Stacks
>>> enabled,
>>
>> The code just does it when shadow stack is enabled.
> 
> Doh.  Fixed that and the EMULATION_FAILED typo Chao pointed out:
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8b31dfcb1de9..06a88a2b08d7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12194,9 +12194,9 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int idt_index,
>                   */
>                  if (__kvm_emulate_msr_read(vcpu, MSR_IA32_U_CET, &u_cet) ||
>                      __kvm_emulate_msr_read(vcpu, MSR_IA32_S_CET, &s_cet))
> -                       return EMULATION_FAILED;
> +                       goto unhandled_task_switch;
>   
> -               if ((u_cet | s_cet) & CET_SHSTK_EN)
> +               if ((u_cet | s_cet) & (CET_ENDBR_EN | CET_SHSTK_EN))
>                          goto unhandled_task_switch;
>          }

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>