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

Claudio Imbrenda
2022-02-15T00:00:42Z

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)