x86/sev: Change snp_guest_issue_request()'s fw_err argument

The GHCB specification declares that the firmware error value for
a guest request will be stored in the lower 32 bits of EXIT_INFO_2.  The
upper 32 bits are for the VMM's own error code. The fw_err argument to
snp_guest_issue_request() is thus a misnomer, and callers will need
access to all 64 bits.

The type of unsigned long also causes problems, since sw_exit_info2 is
u64 (unsigned long long) vs the argument's unsigned long*. Change this
type for issuing the guest request. Pass the ioctl command struct's error
field directly instead of in a local variable, since an incomplete guest
request may not set the error code, and uninitialized stack memory would
be written back to user space.

The firmware might not even be called, so bookend the call with the no
firmware call error and clear the error.

Since the "fw_err" field is really exitinfo2 split into the upper bits'
vmm error code and lower bits' firmware error code, convert the 64 bit
value to a union.

  [ bp:
   - Massage commit message
   - adjust code
   - Fix a build issue as
   Reported-by: kernel test robot <lkp@intel.com>
   Link: https://lore.kernel.org/oe-kbuild-all/202303070609.vX6wp2Af-lkp@intel.com
   - print exitinfo2 in hex
   Tom:
    - Correct -EIO exit case. ]

Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230214164638.1189804-5-dionnaglaze@google.com
Link: https://lore.kernel.org/r/20230307192449.24732-12-bp@alien8.de

1 files changed, 13 insertions, 7 deletions

diff --git a/Documentation/virt/coco/sev-guest.rst b/Documentation/virt/coco/sev-guest.rst
index aa3e4c6a1f90..68b0d2363af8 100644
--- a/Documentation/virt/coco/sev-guest.rst
+++ b/Documentation/virt/coco/sev-guest.rst
@@ -37,11 +37,11 @@ along with a description:
       the return value.  General error numbers (-ENOMEM, -EINVAL)
       are not detailed, but errors with specific meanings are.
 
-The guest ioctl should be issued on a file descriptor of the /dev/sev-guest device.
-The ioctl accepts struct snp_user_guest_request. The input and output structure is
-specified through the req_data and resp_data field respectively. If the ioctl fails
-to execute due to a firmware error, then fw_err code will be set. Otherwise, fw_err
-will be set to 0x00000000ffffffff, i.e., the lower 32-bits are -1.
+The guest ioctl should be issued on a file descriptor of the /dev/sev-guest
+device.  The ioctl accepts struct snp_user_guest_request. The input and
+output structure is specified through the req_data and resp_data field
+respectively. If the ioctl fails to execute due to a firmware error, then
+the fw_error code will be set, otherwise fw_error will be set to -1.
 
 The firmware checks that the message sequence counter is one greater than
 the guests message sequence counter. If guest driver fails to increment message
@@ -57,8 +57,14 @@ counter (e.g. counter overflow), then -EIO will be returned.
                 __u64 req_data;
                 __u64 resp_data;
 
-                /* firmware error code on failure (see psp-sev.h) */
-                __u64 fw_err;
+                /* bits[63:32]: VMM error code, bits[31:0] firmware error code (see psp-sev.h) */
+                union {
+                        __u64 exitinfo2;
+                        struct {
+                                __u32 fw_error;
+                                __u32 vmm_error;
+                        };
+                };
         };
 
 2.1 SNP_GET_REPORT