linux-kernel - Re: [PATCH v8 2/8] KVM: Extend the memslot to support fd-based private memory

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Date:   Thu, 29 Sep 2022 15:45:16 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
        qemu-devel@...gnu.org, Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        Muchun Song <songmuchun@...edance.com>, wei.w.wang@...el.com,
        isaku.yamahata@...il.com
Subject: Re: [PATCH v8 2/8] KVM: Extend the memslot to support fd-based
 private memory

On Thu, Sep 15, 2022 at 10:29:07PM +0800,
Chao Peng <chao.p.peng@...ux.intel.com> wrote:
...
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 584a5bab3af3..12dc0dc57b06 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
...
> @@ -4622,6 +4622,33 @@ static int kvm_vm_ioctl_get_stats_fd(struct kvm *kvm)
>  	return fd;
>  }
>  
> +#define SANITY_CHECK_MEM_REGION_FIELD(field)					\
> +do {										\
> +	BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=		\
> +		     offsetof(struct kvm_userspace_memory_region, field));	\
> +	BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=		\
> +		     sizeof_field(struct kvm_userspace_memory_region, field));	\
> +} while (0)
> +
> +#define SANITY_CHECK_MEM_REGION_EXT_FIELD(field)					\
> +do {											\
> +	BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=			\
> +		     offsetof(struct kvm_userspace_memory_region_ext, field));		\
> +	BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=			\
> +		     sizeof_field(struct kvm_userspace_memory_region_ext, field));	\
> +} while (0)
> +
> +static void kvm_sanity_check_user_mem_region_alias(void)
> +{
> +	SANITY_CHECK_MEM_REGION_FIELD(slot);
> +	SANITY_CHECK_MEM_REGION_FIELD(flags);
> +	SANITY_CHECK_MEM_REGION_FIELD(guest_phys_addr);
> +	SANITY_CHECK_MEM_REGION_FIELD(memory_size);
> +	SANITY_CHECK_MEM_REGION_FIELD(userspace_addr);
> +	SANITY_CHECK_MEM_REGION_EXT_FIELD(private_offset);
> +	SANITY_CHECK_MEM_REGION_EXT_FIELD(private_fd);
> +}
> +
>  static long kvm_vm_ioctl(struct file *filp,
>  			   unsigned int ioctl, unsigned long arg)
>  {
> @@ -4645,14 +4672,20 @@ static long kvm_vm_ioctl(struct file *filp,
>  		break;
>  	}
>  	case KVM_SET_USER_MEMORY_REGION: {
> -		struct kvm_userspace_memory_region kvm_userspace_mem;
> +		struct kvm_user_mem_region mem;
> +		unsigned long size = sizeof(struct kvm_userspace_memory_region);
> +
> +		kvm_sanity_check_user_mem_region_alias();
>  
>  		r = -EFAULT;
> -		if (copy_from_user(&kvm_userspace_mem, argp,
> -						sizeof(kvm_userspace_mem)))
> +		if (copy_from_user(&mem, argp, size);
> +			goto out;
> +
> +		r = -EINVAL;
> +		if (mem.flags & KVM_MEM_PRIVATE)
>  			goto out;

Nit:  It's better to check if padding is zero.  Maybe rename it to reserved.

+               if (mem.pad1 || memchr_inv(mem.pad2, 0, sizeof(mem.pad2)))
+                       goto out;
-- 
Isaku Yamahata <isaku.yamahata@...il.com>