KVM: s390: gaccess: Check if guest address is in memslot

Previously, access_guest_page() did not check whether the given guest
address is inside of a memslot. This is not a problem, since
kvm_write_guest_page/kvm_read_guest_page return -EFAULT in this case.

However, -EFAULT is also returned when copy_to/from_user fails.

When emulating a guest instruction, the address being outside a memslot
usually means that an addressing exception should be injected into the
guest.

Failure in copy_to/from_user however indicates that something is wrong
in userspace and hence should be handled there.

To be able to distinguish these two cases, return PGM_ADDRESSING in
access_guest_page() when the guest address is outside guest memory. In
access_guest_real(), populate vcpu->arch.pgm.code such that
kvm_s390_inject_prog_cond() can be used in the caller for injecting into
the guest (if applicable).

Since this adds a new return value to access_guest_page(), we need to make
sure that other callers are not confused by the new positive return value.

There are the following users of access_guest_page():
- access_guest_with_key() does the checking itself (in
  guest_range_to_gpas()), so this case should never happen. Even if, the
  handling is set up properly.
- access_guest_real() just passes the return code to its callers, which
  are:
    - read_guest_real() - see below
    - write_guest_real() - see below

There are the following users of read_guest_real():
- ar_translation() in gaccess.c which already returns PGM_*
- setup_apcb10(), setup_apcb00(), setup_apcb11() in vsie.c which always
  return -EFAULT on read_guest_read() nonzero return - no change
- shadow_crycb(), handle_stfle() always present this as validity, this
  could be handled better but doesn't change current behaviour - no change

There are the following users of write_guest_real():
- kvm_s390_store_status_unloaded() always returns -EFAULT on
  write_guest_real() failure.

Fixes: 2293897805c2 ("KVM: s390: add architecture compliant guest access functions")
Cc: [email protected]
Signed-off-by: Nico Boehr <[email protected]>
Reviewed-by: Heiko Carstens <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Acked-by: Janosch Frank <[email protected]>
Signed-off-by: Heiko Carstens <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index e65f597e3044..a688351f4ab5 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -828,6 +828,8 @@ static int access_guest_page(struct kvm *kvm, enum gacc_mode mode, gpa_t gpa,
 	const gfn_t gfn = gpa_to_gfn(gpa);
 	int rc;
 
+	if (!gfn_to_memslot(kvm, gfn))
+		return PGM_ADDRESSING;
 	if (mode == GACC_STORE)
 		rc = kvm_write_guest_page(kvm, gfn, data, offset, len);
 	else
@@ -985,6 +987,8 @@ int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra,
 		gra += fragment_len;
 		data += fragment_len;
 	}
+	if (rc > 0)
+		vcpu->arch.pgm.code = rc;
 	return rc;
 }