Re: [PATCH v4 06/10] KVM: s390: Add vm IOCTL for key checked guest absolute memory access

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Fri, 11 Feb 2022 19:22:11 +0100
Janis Schoetterl-Glausch <scgl@linux.ibm.com> wrote:

> Channel I/O honors storage keys and is performed on absolute memory.
> For I/O emulation user space therefore needs to be able to do key
> checked accesses.
> The vm IOCTL supports read/write accesses, as well as checking
> if an access would succeed.
> Unlike relying on KVM_S390_GET_SKEYS for key checking would,
> the vm IOCTL performs the check in lockstep with the read or write,
> by, ultimately, mapping the access to move instructions that
> support key protection checking with a supplied key.
> Fetch and storage protection override are not applicable to absolute
> accesses and so are not applied as they are when using the vcpu memop.
> 
> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
> Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> ---
>  arch/s390/kvm/gaccess.c  | 72 +++++++++++++++++++++++++++++++++++
>  arch/s390/kvm/gaccess.h  |  6 +++
>  arch/s390/kvm/kvm-s390.c | 81 ++++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/kvm.h |  2 +
>  4 files changed, 161 insertions(+)
> 
> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> index 37838f637707..d53a183c2005 100644
> --- a/arch/s390/kvm/gaccess.c
> +++ b/arch/s390/kvm/gaccess.c
> @@ -795,6 +795,35 @@ static int low_address_protection_enabled(struct kvm_vcpu *vcpu,
>  	return 1;
>  }
>  
> +static int vm_check_access_key(struct kvm *kvm, u8 access_key,
> +			       enum gacc_mode mode, gpa_t gpa)
> +{
> +	u8 storage_key, access_control;
> +	bool fetch_protected;
> +	unsigned long hva;
> +	int r;
> +
> +	if (access_key == 0)
> +		return 0;
> +
> +	hva = gfn_to_hva(kvm, gpa_to_gfn(gpa));
> +	if (kvm_is_error_hva(hva))
> +		return PGM_ADDRESSING;
> +
> +	mmap_read_lock(current->mm);
> +	r = get_guest_storage_key(current->mm, hva, &storage_key);
> +	mmap_read_unlock(current->mm);
> +	if (r)
> +		return r;
> +	access_control = FIELD_GET(_PAGE_ACC_BITS, storage_key);
> +	if (access_control == access_key)
> +		return 0;
> +	fetch_protected = storage_key & _PAGE_FP_BIT;
> +	if ((mode == GACC_FETCH || mode == GACC_IFETCH) && !fetch_protected)
> +		return 0;
> +	return PGM_PROTECTION;
> +}
> +
>  static bool fetch_prot_override_applicable(struct kvm_vcpu *vcpu, enum gacc_mode mode,
>  					   union asce asce)
>  {
> @@ -994,6 +1023,26 @@ access_guest_page_with_key(struct kvm *kvm, enum gacc_mode mode, gpa_t gpa,
>  	return 0;
>  }
>  
> +int access_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, void *data,
> +			      unsigned long len, enum gacc_mode mode, u8 access_key)
> +{
> +	int offset = offset_in_page(gpa);
> +	int fragment_len;
> +	int rc;
> +
> +	while (min(PAGE_SIZE - offset, len) > 0) {
> +		fragment_len = min(PAGE_SIZE - offset, len);
> +		rc = access_guest_page_with_key(kvm, mode, gpa, data, fragment_len, access_key);
> +		if (rc)
> +			return rc;
> +		offset = 0;
> +		len -= fragment_len;
> +		data += fragment_len;
> +		gpa += fragment_len;
> +	}
> +	return 0;
> +}
> +
>  int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
>  			  void *data, unsigned long len, enum gacc_mode mode,
>  			  u8 access_key)
> @@ -1144,6 +1193,29 @@ int check_gva_range(struct kvm_vcpu *vcpu, unsigned long gva, u8 ar,
>  	return rc;
>  }
>  
> +/**
> + * check_gpa_range - test a range of guest physical addresses for accessibility
> + * @kvm: virtual machine instance
> + * @gpa: guest physical address
> + * @length: length of test range
> + * @mode: access mode to test, relevant for storage keys
> + * @access_key: access key to mach the storage keys with
> + */
> +int check_gpa_range(struct kvm *kvm, unsigned long gpa, unsigned long length,
> +		    enum gacc_mode mode, u8 access_key)
> +{
> +	unsigned int fragment_len;
> +	int rc = 0;
> +
> +	while (length && !rc) {
> +		fragment_len = min(PAGE_SIZE - offset_in_page(gpa), length);
> +		rc = vm_check_access_key(kvm, access_key, mode, gpa);
> +		length -= fragment_len;
> +		gpa += fragment_len;
> +	}
> +	return rc;
> +}
> +
>  /**
>   * kvm_s390_check_low_addr_prot_real - check for low-address protection
>   * @vcpu: virtual cpu
> diff --git a/arch/s390/kvm/gaccess.h b/arch/s390/kvm/gaccess.h
> index c5f2e7311b17..1124ff282012 100644
> --- a/arch/s390/kvm/gaccess.h
> +++ b/arch/s390/kvm/gaccess.h
> @@ -193,6 +193,12 @@ int guest_translate_address_with_key(struct kvm_vcpu *vcpu, unsigned long gva, u
>  int check_gva_range(struct kvm_vcpu *vcpu, unsigned long gva, u8 ar,
>  		    unsigned long length, enum gacc_mode mode, u8 access_key);
>  
> +int check_gpa_range(struct kvm *kvm, unsigned long gpa, unsigned long length,
> +		    enum gacc_mode mode, u8 access_key);
> +
> +int access_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, void *data,
> +			      unsigned long len, enum gacc_mode mode, u8 access_key);
> +
>  int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
>  			  void *data, unsigned long len, enum gacc_mode mode,
>  			  u8 access_key);
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index c31b40abfa23..36bc73b5f5de 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2364,6 +2364,78 @@ static bool access_key_invalid(u8 access_key)
>  	return access_key > 0xf;
>  }
>  
> +static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
> +{
> +	void __user *uaddr = (void __user *)mop->buf;
> +	u64 supported_flags;
> +	void *tmpbuf = NULL;
> +	int r, srcu_idx;
> +
> +	supported_flags = KVM_S390_MEMOP_F_SKEY_PROTECTION
> +			  | KVM_S390_MEMOP_F_CHECK_ONLY;
> +	if (mop->flags & ~supported_flags)
> +		return -EINVAL;
> +	if (mop->size > MEM_OP_MAX_SIZE)
> +		return -E2BIG;
> +	if (kvm_s390_pv_is_protected(kvm))
> +		return -EINVAL;
> +	if (mop->flags & KVM_S390_MEMOP_F_SKEY_PROTECTION) {
> +		if (access_key_invalid(mop->key))
> +			return -EINVAL;
> +	} else {
> +		mop->key = 0;
> +	}
> +	if (!(mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY)) {
> +		tmpbuf = vmalloc(mop->size);
> +		if (!tmpbuf)
> +			return -ENOMEM;
> +	}
> +
> +	srcu_idx = srcu_read_lock(&kvm->srcu);
> +
> +	if (kvm_is_error_gpa(kvm, mop->gaddr)) {
> +		r = PGM_ADDRESSING;
> +		goto out_unlock;
> +	}
> +
> +	switch (mop->op) {
> +	case KVM_S390_MEMOP_ABSOLUTE_READ: {
> +		if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) {
> +			r = check_gpa_range(kvm, mop->gaddr, mop->size, GACC_FETCH, mop->key);
> +		} else {
> +			r = access_guest_abs_with_key(kvm, mop->gaddr, tmpbuf,
> +						      mop->size, GACC_FETCH, mop->key);
> +			if (r == 0) {
> +				if (copy_to_user(uaddr, tmpbuf, mop->size))
> +					r = -EFAULT;
> +			}
> +		}
> +		break;
> +	}
> +	case KVM_S390_MEMOP_ABSOLUTE_WRITE: {
> +		if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) {
> +			r = check_gpa_range(kvm, mop->gaddr, mop->size, GACC_STORE, mop->key);
> +		} else {
> +			if (copy_from_user(tmpbuf, uaddr, mop->size)) {
> +				r = -EFAULT;
> +				break;
> +			}
> +			r = access_guest_abs_with_key(kvm, mop->gaddr, tmpbuf,
> +						      mop->size, GACC_STORE, mop->key);
> +		}
> +		break;
> +	}
> +	default:
> +		r = -EINVAL;
> +	}
> +
> +out_unlock:
> +	srcu_read_unlock(&kvm->srcu, srcu_idx);
> +
> +	vfree(tmpbuf);
> +	return r;
> +}
> +
>  long kvm_arch_vm_ioctl(struct file *filp,
>  		       unsigned int ioctl, unsigned long arg)
>  {
> @@ -2488,6 +2560,15 @@ long kvm_arch_vm_ioctl(struct file *filp,
>  		}
>  		break;
>  	}
> +	case KVM_S390_MEM_OP: {
> +		struct kvm_s390_mem_op mem_op;
> +
> +		if (copy_from_user(&mem_op, argp, sizeof(mem_op)) == 0)
> +			r = kvm_s390_vm_mem_op(kvm, &mem_op);
> +		else
> +			r = -EFAULT;
> +		break;
> +	}
>  	default:
>  		r = -ENOTTY;
>  	}
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 4566f429db2c..4bc7623def87 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -575,6 +575,8 @@ struct kvm_s390_mem_op {
>  #define KVM_S390_MEMOP_LOGICAL_WRITE	1
>  #define KVM_S390_MEMOP_SIDA_READ	2
>  #define KVM_S390_MEMOP_SIDA_WRITE	3
> +#define KVM_S390_MEMOP_ABSOLUTE_READ	4
> +#define KVM_S390_MEMOP_ABSOLUTE_WRITE	5
>  /* flags for kvm_s390_mem_op->flags */
>  #define KVM_S390_MEMOP_F_CHECK_ONLY		(1ULL << 0)
>  #define KVM_S390_MEMOP_F_INJECT_EXCEPTION	(1ULL << 1)