linux-kernel - Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

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Message-ID: <jpgzj4w9nj7.fsf@redhat.com>
Date:	Fri, 22 May 2015 19:54:03 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	pbonzini@...hat.com, gleb@...nel.org, mtosatti@...hat.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

Boris Ostrovsky <boris.ostrovsky@...cle.com> writes:

> On 05/11/2015 10:55 AM, Xiao Guangrong wrote:
>> KVM may turn a user page to a kernel page when kernel writes a readonly
>> user page if CR0.WP = 1. This shadow page entry will be reused after
>> SMAP is enabled so that kernel is allowed to access this user page
>>
>> Fix it by setting SMAP && !CR0.WP into shadow page's role and reset mmu
>> once CR4.SMAP is updated
>>
>> Signed-off-by: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
>> ---
>
>
>>
>> @@ -4208,12 +4211,18 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
>>   		       const u8 *new, int bytes)
>>   {
>>   	gfn_t gfn = gpa >> PAGE_SHIFT;
>> -	union kvm_mmu_page_role mask = { .word = 0 };
>>   	struct kvm_mmu_page *sp;
>>   	LIST_HEAD(invalid_list);
>>   	u64 entry, gentry, *spte;
>>   	int npte;
>>   	bool remote_flush, local_flush, zap_page;
>> +	union kvm_mmu_page_role mask = (union kvm_mmu_page_role) {
>> +		.cr0_wp = 1,
>> +		.cr4_pae = 1,
>> +		.nxe = 1,
>> +		.smep_andnot_wp = 1,
>> +		.smap_andnot_wp = 1,
>> +	};
>>
>>
>
>
> This breaks older compilers that can't initialize anon structures.

How old ? Even gcc 3.1 says you can use unnamed struct/union fields and
3.2 is the minimum version required to compile the kernel as mentioned
in the README.

We could simply just name the structure, but I doubt this is the
only place in the kernel code where it's being used this way :)

Bandan

> -boris
> --
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