Re: [PATCH v3 06/10] KVM: s390: Add vm IOCTL for key checked guest absolute memory access

From: Claudio Imbrenda
Date: Thu Feb 10 2022 - 11:26:14 EST

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In reply to: Christian Borntraeger: "Re: [PATCH v3 06/10] KVM: s390: Add vm IOCTL for key checked guest absolute memory access"
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On Thu, 10 Feb 2022 15:40:03 +0100
Christian Borntraeger <borntraeger@xxxxxxxxxxxxx> wrote:

> Am 09.02.22 um 18:04 schrieb Janis Schoetterl-Glausch:
> > 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@xxxxxxxxxxxxx>
> > Acked-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
>
> same comment that you did for the vcpu part (default key)
> with that.
>
> Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>

I guess @linux.ibm.com ?

> > ---
> > arch/s390/kvm/gaccess.c | 72 ++++++++++++++++++++++++++++++++++++
> > arch/s390/kvm/gaccess.h | 6 +++
> > arch/s390/kvm/kvm-s390.c | 79 ++++++++++++++++++++++++++++++++++++++++
> > include/uapi/linux/kvm.h | 2 +
> > 4 files changed, 159 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 85763ec7bc60..7ee3d2e8ecf2 100644
> > --- a/arch/s390/kvm/kvm-s390.c
> > +++ b/arch/s390/kvm/kvm-s390.c
> > @@ -2365,6 +2365,76 @@ 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;
> > + }
> > + 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)
> > {
> > @@ -2489,6 +2559,15 @@ 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 44558cf4c52e..b83c9286e017 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)

Next message: Ricardo Rivera-Matos: "[RESEND v2 2/2] power: supply: bq25980: Implements POWER_SUPPLY_CHARGE_TYPE_BYPASS"
Previous message: Kalle Valo: "Re: [PATCH v9 05/24] wfx: add main.c/main.h"
In reply to: Christian Borntraeger: "Re: [PATCH v3 06/10] KVM: s390: Add vm IOCTL for key checked guest absolute memory access"
Next in thread: Janis Schoetterl-Glausch: "[PATCH v3 10/10] KVM: s390: selftests: Test memops with storage keys"
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