linux-kernel - Re: [PATCH v3 05/10] KVM: s390: Add optional storage key checking to MEMOP IOCTL

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Message-ID: <c5d8e633-c0cd-91d4-723b-abf26c01fd6d@linux.ibm.com>
Date:   Thu, 10 Feb 2022 10:29:45 +0100
From:   Christian Borntraeger <borntraeger@...ux.ibm.com>
To:     Janis Schoetterl-Glausch <scgl@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     Alexander Gordeev <agordeev@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Jonathan Corbet <corbet@....net>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>
Subject: Re: [PATCH v3 05/10] KVM: s390: Add optional storage key checking to
 MEMOP IOCTL

Am 09.02.22 um 18:04 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.
> 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>

Claudio, Janosch, can you confirm that this is still valid?


Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>

minor thing below
> ---
>   arch/s390/kvm/kvm-s390.c | 30 ++++++++++++++++++++----------
>   include/uapi/linux/kvm.h |  6 +++++-
>   2 files changed, 25 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index cf347e1a4f17..85763ec7bc60 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>

do we still need that after the changes?

>   
>   #include <asm/asm-offsets.h>
>   #include <asm/lowcore.h>
> @@ -2359,6 +2360,11 @@ static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
>   	return r;
>   }
>   
> +static bool access_key_invalid(u8 access_key)
> +{
> +	return access_key > 0xf;
> +}
> +
>   long kvm_arch_vm_ioctl(struct file *filp,
>   		       unsigned int ioctl, unsigned long arg)
>   {
> @@ -4690,17 +4696,19 @@ static long kvm_s390_guest_mem_op(struct kvm_vcpu *vcpu,
>   	void *tmpbuf = NULL;
>   	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_SKEY_PROTECTION;
>   
>   	if (mop->flags & ~supported_flags || mop->ar >= NUM_ACRS || !mop->size)
>   		return -EINVAL;
> -
>   	if (mop->size > MEM_OP_MAX_SIZE)
>   		return -E2BIG;
> -
>   	if (kvm_s390_pv_cpu_is_protected(vcpu))
>   		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)
> @@ -4710,11 +4718,12 @@ static long kvm_s390_guest_mem_op(struct kvm_vcpu *vcpu,
>   	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, mop->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, mop->key);
>   		if (r == 0) {
>   			if (copy_to_user(uaddr, tmpbuf, mop->size))
>   				r = -EFAULT;
> @@ -4722,15 +4731,16 @@ 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, mop->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, mop->key);
>   		break;
>   	}
>   
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index b46bcdb0cab1..44558cf4c52e 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;	/* access key, ignored if flag unset */
> +		};
>   		__u32 sida_offset; /* offset into the sida */
>   		__u8 reserved[32]; /* should be set to 0 */
>   	};
> @@ -575,6 +578,7 @@ 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_SKEY_PROTECTION	(1ULL << 2)
>   
>   /* for KVM_INTERRUPT */
>   struct kvm_interrupt {