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Message-ID: <2bd8dd31-0c08-a03b-33b3-67d7adc78726@linux.ibm.com>
Date: Tue, 18 Jan 2022 12:51:26 +0100
From: Christian Borntraeger <borntraeger@...ux.ibm.com>
To: Janis Schoetterl-Glausch <scgl@...ux.ibm.com>,
Janosch Frank <frankja@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@...ux.ibm.com>,
David Hildenbrand <david@...hat.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
kvm@...r.kernel.org, linux-s390@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 05/10] KVM: s390: Add optional storage key checking
to MEMOP IOCTL
Am 18.01.22 um 10:52 schrieb Janis Schoetterl-Glausch:
> User space needs a mechanism to perform key checked accesses when
> emulating instructions.
>
> The key can be passed as an additional argument via the flags field.
> As reserved flags need to be 0, and key 0 matches all storage keys,
> by default no key checking is performed, as before.
> Having an additional argument is flexible, as user space can
> pass the guest PSW's key, in order to make an access the same way the
> CPU would, or pass another key if necessary.
>
> Signed-off-by: Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
> Acked-by: Janosch Frank <frankja@...ux.ibm.com>
> Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> ---
> arch/s390/kvm/kvm-s390.c | 21 ++++++++++++++-------
> include/uapi/linux/kvm.h | 1 +
> 2 files changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 38b304e81c57..c4acdb025ff1 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -32,6 +32,7 @@
> #include <linux/sched/signal.h>
> #include <linux/string.h>
> #include <linux/pgtable.h>
> +#include <linux/bitfield.h>
>
> #include <asm/asm-offsets.h>
> #include <asm/lowcore.h>
> @@ -4727,9 +4728,11 @@ static long kvm_s390_guest_mem_op(struct kvm_vcpu *vcpu,
> {
> void __user *uaddr = (void __user *)mop->buf;
> void *tmpbuf = NULL;
> + char access_key = 0;
> int r = 0;
> const u64 supported_flags = KVM_S390_MEMOP_F_INJECT_EXCEPTION
> - | KVM_S390_MEMOP_F_CHECK_ONLY;
> + | KVM_S390_MEMOP_F_CHECK_ONLY
> + | KVM_S390_MEMOP_F_SKEYS_ACC;
I think it would be better to just have a flag here (single bit) to check the key and
then embed the key value in the payload.
union {
__u8 ar; /* the access register number */
__u32 sida_offset; /* offset into the sida */
__u8 reserved[32]; /* should be set to 0 */
};
There are cases when we need both, AR and key so maybe an unname struct is the easiest.
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 1daa45268de2..e8fa1f82d472 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -562,7 +562,10 @@ struct kvm_s390_mem_op {
__u32 op; /* type of operation */
__u64 buf; /* buffer in userspace */
union {
- __u8 ar; /* the access register number */
+ struct {
+ __u8 ar; /* the access register number */
+ __u8 key; /* effective storage key */
+ };
__u32 sida_offset; /* offset into the sida */
__u8 reserved[32]; /* should be set to 0 */
};
(or acc instead of key)
>
> if (mop->flags & ~supported_flags || mop->ar >= NUM_ACRS || !mop->size)
> return -EINVAL;
> @@ -4746,14 +4749,17 @@ static long kvm_s390_guest_mem_op(struct kvm_vcpu *vcpu,
> return -ENOMEM;
> }
>
> + access_key = FIELD_GET(KVM_S390_MEMOP_F_SKEYS_ACC, mop->flags);
> +
> switch (mop->op) {
> case KVM_S390_MEMOP_LOGICAL_READ:
> if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) {
> - r = check_gva_range(vcpu, mop->gaddr, mop->ar,
> - mop->size, GACC_FETCH, 0);
> + r = check_gva_range(vcpu, mop->gaddr, mop->ar, mop->size,
> + GACC_FETCH, access_key);
> break;
> }
> - r = read_guest(vcpu, mop->gaddr, mop->ar, tmpbuf, mop->size);
> + r = read_guest_with_key(vcpu, mop->gaddr, mop->ar, tmpbuf,
> + mop->size, access_key);
> if (r == 0) {
> if (copy_to_user(uaddr, tmpbuf, mop->size))
> r = -EFAULT;
> @@ -4761,15 +4767,16 @@ static long kvm_s390_guest_mem_op(struct kvm_vcpu *vcpu,
> break;
> case KVM_S390_MEMOP_LOGICAL_WRITE:
> if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) {
> - r = check_gva_range(vcpu, mop->gaddr, mop->ar,
> - mop->size, GACC_STORE, 0);
> + r = check_gva_range(vcpu, mop->gaddr, mop->ar, mop->size,
> + GACC_STORE, access_key);
> break;
> }
> if (copy_from_user(tmpbuf, uaddr, mop->size)) {
> r = -EFAULT;
> break;
> }
> - r = write_guest(vcpu, mop->gaddr, mop->ar, tmpbuf, mop->size);
> + r = write_guest_with_key(vcpu, mop->gaddr, mop->ar, tmpbuf,
> + mop->size, access_key);
> break;
> }
>
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 1daa45268de2..e3f450b2f346 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -575,6 +575,7 @@ struct kvm_s390_mem_op {
> /* 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)
> +#define KVM_S390_MEMOP_F_SKEYS_ACC 0x0f00ULL
>
> /* for KVM_INTERRUPT */
> struct kvm_interrupt {
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