linux-kernel - Re: [PATCH v2 7/9] KVM: x86/xen: Drop RAX[63:32] when processing hypercall

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <2ddcc979-519c-a38c-065f-a9036cc2b58e@redhat.com>
Date:   Thu, 22 Apr 2021 12:35:06 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Babu Moger <babu.moger@....com>,
        Joao Martins <joao.m.martins@...cle.com>,
        David Woodhouse <dwmw@...zon.co.uk>
Subject: Re: [PATCH v2 7/9] KVM: x86/xen: Drop RAX[63:32] when processing
 hypercall

On 22/04/21 11:51, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@...gle.com> writes:
> 
>> Truncate RAX to 32 bits, i.e. consume EAX, when retrieving the hypecall
>> index for a Xen hypercall.  Per Xen documentation[*], the index is EAX
>> when the vCPU is not in 64-bit mode.
>>
>> [*] http://xenbits.xenproject.org/docs/sphinx-unstable/guest-guide/x86/hypercall-abi.html
>>
>> Fixes: 23200b7a30de ("KVM: x86/xen: intercept xen hypercalls if enabled")
>> Cc: Joao Martins <joao.m.martins@...cle.com>
>> Cc: David Woodhouse <dwmw@...zon.co.uk>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
>> ---
>>   arch/x86/kvm/xen.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
>> index ae17250e1efe..7f27bb65a572 100644
>> --- a/arch/x86/kvm/xen.c
>> +++ b/arch/x86/kvm/xen.c
>> @@ -673,7 +673,7 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)
>>   	bool longmode;
>>   	u64 input, params[6];
>>   
>> -	input = (u64)kvm_register_read(vcpu, VCPU_REGS_RAX);
>> +	input = (u64)kvm_register_readl(vcpu, VCPU_REGS_RAX);
>>   
>>   	/* Hyper-V hypercalls get bit 31 set in EAX */
>>   	if ((input & 0x80000000) &&
> 
> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> 
> Alternatively, as a minor optimization, you could've used '!longmode'
> check below, something like:
> 
> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
> index ae17250e1efe..7df1498d3a41 100644
> --- a/arch/x86/kvm/xen.c
> +++ b/arch/x86/kvm/xen.c
> @@ -682,6 +682,7 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)
>   
>          longmode = is_64_bit_mode(vcpu);
>          if (!longmode) {
> +               input = (u32)input;
>                  params[0] = (u32)kvm_rbx_read(vcpu);
>                  params[1] = (u32)kvm_rcx_read(vcpu);
>                  params[2] = (u32)kvm_rdx_read(vcpu);
> 

You haven't seen patch 9 yet. :)

Paolo