From: Avi Kivity <avi@redhat.com>
To: "Yang, Wei Y" <wei.y.yang@intel.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: [Patch v3] Enable CPU SMEP feature for KVM
Date: Fri, 27 May 2011 11:45:29 +0300 [thread overview]
Message-ID: <4DDF64A9.1000001@redhat.com> (raw)
In-Reply-To: <5D8008F58939784290FAB48F54975198419FBE82D2@shsmsx502.ccr.corp.intel.com>
On 05/26/2011 04:28 PM, Yang, Wei Y wrote:
> This patchset enables a new CPU feature SMEP (Supervisor Mode Execution
> Protection) in KVM. SMEP prevents kernel from executing code in application.
> Updated Intel SDM describes this CPU feature. The document will be published soon.
>
> This patchset is based on Fenghua's SMEP patch series, as referred by:
> https://lkml.org/lkml/2011/5/17/523
>
>
>
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index 6c4dc01..7e0b2f8 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -120,7 +120,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
> struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> gva_t addr, u32 access)
> {
> - pt_element_t pte;
> + pt_element_t pte, pte_smep;
> pt_element_t __user *ptep_user;
> gfn_t table_gfn;
> unsigned index, pt_access, uninitialized_var(pte_access);
> @@ -150,7 +150,11 @@ walk:
> }
> --walker->level;
> }
> + pte_smep = ~0ULL;
> +#else
> + pte_smep = ~0U;
> #endif
Use pte_smep = ~(pt_element_t)0;. But I don't understand why you don't
use pt_access instead.
>
> + if (unlikely(fetch_fault&& !user_fault))
Why are kernel fetch faults unlikely? Rather, a SMEP fault is unlikely,
so annotate that instead.
> + if ((vcpu->arch.cr4& X86_CR4_SMEP)
> + && (pte_smep& PT_USER_MASK))
> + eperm = true;
> +
kvm_read_cr4_bits()
> gfn = gpte_to_gfn_lvl(pte, lvl);
> gfn += (addr& PT_LVL_OFFSET_MASK(lvl))>> PAGE_SHIFT;
>
> @@ -305,7 +316,7 @@ error:
>
> walker->fault.error_code |= write_fault | user_fault;
>
> - if (fetch_fault&& mmu->nx)
> + if (fetch_fault&& (mmu->nx || (vcpu->arch.cr4& X86_CR4_SMEP)))
Here, too.
> @@ -4507,6 +4507,15 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
> }
> }
> }
> +
> + best = kvm_find_cpuid_entry(vcpu, 7, 0);
> + if (best&& (best->ebx& bit(X86_FEATURE_SMEP))) {
> + if (boot_cpu_has(X86_FEATURE_SMEP))
> + vcpu->arch.cr4_reserved_bits&=
> + ~((unsigned long)X86_CR4_SMEP);
Fails if cpuid is updated again to include SMEP. But I suggest to drop
cr4_reserved_bits completely and just check cpuid directly in
kvm_set_cr4(), if cr4.smep is changed, which should be very rare. See
how XSAVE is supported, for example.
> + else
> + best->ebx&= ~(bit(X86_FEATURE_SMEP));
Not needed - x86.c already masks unsupported features.
> + }
> }
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
next prev parent reply other threads:[~2011-05-27 8:45 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-26 13:28 [Patch v3] Enable CPU SMEP feature for KVM Yang, Wei Y
2011-05-27 2:56 ` Tian, Kevin
2011-05-27 8:47 ` Avi Kivity
2011-05-27 8:45 ` Avi Kivity [this message]
2011-05-29 5:16 ` Li, Xin
2011-05-29 6:42 ` Avi Kivity
2011-05-29 7:15 ` Li, Xin
2011-05-29 7:20 ` Avi Kivity
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