[PATCH v6 0/1] Improve zcrypt reply message verification checks

[Harald Freudenberger <freude@linux.ibm.com>]

Add or improve checks related to buffer sizes and reply sizes to the
handling of replies from the crypto cards for CCA, EP11 (AP message
type 6) and ICA (AP type 50) messages. The verification code related
to reply field length was not designed well and thus firmware
deficiencies could lead to unexpected behavior in the zcrypt device
driver. Thus improve the code to more closely inspect especially
length fields at message replies.

Rework zcrypt_msgtype6_receive(), zcrypt_msgtype6_receive_ep11() and
zcrypt_msgtype50_receive() to validate reply lengths more carefully
before copying data back into the request buffer. Use size_t for
length calculations, reject inconsistent reply sizes, and add
defensive handling for short invalid replies. For XCRB replies,
validate both reply segments and derive the effective message length
from the covered range instead of trusting only the second segment.

Changelog:
v1 - initial patch
v2 - fixed typo in header check_for_overflow -> check_add_overflow.
v3 - rephrased and smoothed subject and text of the patch. It is now
     "s390/zcrypt: Improve zcrypt reply message verification checks"
     and the text does not talk about malicious cards any more.
     Updated Reviewed-by tags
v4 - As sashiko clearly states the addition of two 32 bit values can
     mathematically never overflow a 64 bit value and thus the
     check_add_overflow() was total overkill - removed.
v5 - Sashiko had a by-catch related to the very same fields. Under
     some circumstances the fields count1 and offset1 of the CPRB
     where not checked but used for a memcpy to userspace. So again a
     rework of the check of these x86 header fields in the receiving
     function before the CPRB is processed to be copied in parts to
     userspace. Removed all reviewed-by as I want to have another
     developer look onto this patch again.
v6 - Again reworked and re-structured the code. As the very same
     pattern appears with message type 50 also reworked the receive
     function there.

Harald Freudenberger (1):
  s390/zcrypt: Improve zcrypt reply message verification checks

 drivers/s390/crypto/zcrypt_msgtype50.c |  39 ++++---
 drivers/s390/crypto/zcrypt_msgtype6.c  | 151 ++++++++++++++++---------
 2 files changed, 126 insertions(+), 64 deletions(-)

-- 
2.43.0