linux-kernel - Re: [PATCH v3 5/9] KVM: vmx/pmu: Add MSR_ARCH_LBR

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]

Date:   Wed, 3 Mar 2021 08:58:37 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Like Xu <like.xu@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, wei.w.wang@...el.com,
        Borislav Petkov <bp@...en8.de>, kvm@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 5/9] KVM: vmx/pmu: Add MSR_ARCH_LBR_DEPTH emulation
 for Arch LBR

On Wed, Mar 03, 2021, Like Xu wrote:
> @@ -348,10 +352,26 @@ static bool intel_pmu_handle_lbr_msrs_access(struct kvm_vcpu *vcpu,
>  	return true;
>  }
>  
> +/*
> + * Check if the requested depth values is supported
> + * based on the bits [0:7] of the guest cpuid.1c.eax.
> + */
> +static bool arch_lbr_depth_is_valid(struct kvm_vcpu *vcpu, u64 depth)
> +{
> +	struct kvm_cpuid_entry2 *best;
> +
> +	best = kvm_find_cpuid_entry(vcpu, 0x1c, 0);
> +	if (best && depth && !(depth % 8))

This is still wrong, it fails to weed out depth > 64.

Not that this is a hot path, but it's probably worth double checking that the
compiler generates simple code for "depth % 8", e.g. it can be "depth & 7)".

> +		return (best->eax & 0xff) & (1ULL << (depth / 8 - 1));
> +
> +	return false;
> +}
> +