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, 16 insertions, 2 deletions

diff --git a/include/uapi/linux/sev-guest.h b/include/uapi/linux/sev-guest.h
index 256aaeff7e65..2aa39112cf8d 100644
--- a/include/uapi/linux/sev-guest.h
+++ b/include/uapi/linux/sev-guest.h
@@ -52,8 +52,14 @@ struct snp_guest_request_ioctl {
 	__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;
+		};
+	};
 };
 
 struct snp_ext_report_req {
@@ -77,4 +83,12 @@ struct snp_ext_report_req {
 /* Get SNP extended report as defined in the GHCB specification version 2. */
 #define SNP_GET_EXT_REPORT _IOWR(SNP_GUEST_REQ_IOC_TYPE, 0x2, struct snp_guest_request_ioctl)
 
+/* Guest message request EXIT_INFO_2 constants */
+#define SNP_GUEST_FW_ERR_MASK		GENMASK_ULL(31, 0)
+#define SNP_GUEST_VMM_ERR_SHIFT		32
+#define SNP_GUEST_VMM_ERR(x)		(((u64)x) << SNP_GUEST_VMM_ERR_SHIFT)
+
+#define SNP_GUEST_VMM_ERR_INVALID_LEN	1
+#define SNP_GUEST_VMM_ERR_BUSY		2
+
 #endif /* __UAPI_LINUX_SEV_GUEST_H_ */