[PATCH v2 4/4] crypto/ccp: Do not initialize SNP for ioctl(SNP_CONFIG)

[Tycho Andersen]

From: "Tycho Andersen (AMD)" <tycho@xxxxxxxxxx>

Sashiko notes:

> if SEV initialization fails and KVM is actively running normal VMs, could a
> userspace process trigger this code path via /dev/sev ioctls (e.g.,
> SEV_PDH_GEN) and zero out MSR_VM_HSAVE_PA globally? Would the next VMRUN
> execution for an active VM trigger a general protection fault and crash the
> host?

Refuse to re-try initialization if SNP is not already initialized for
SNP_CONFIG.

This is technically an ABI break: before if SNP initialization failed it
could be transparently retriggered by this ioctl, and if no VMs were
running, everything worked fine. Hopefully this is enough of a corner case
that nobody will notice, but someone does, there are a few options:

* do something like symbol_get() for kvm and refuse to initialize if KVM is
  loaded
* check each cpu's HSAVE_PA for non-zero data before re-initializing
* once initialization has failed, continue to refuse to initialize until
  the ccp module is unloaded

Fixes: ceac7fb89e8d ("crypto: ccp - Ensure implicit SEV/SNP init and shutdown in ioctls")
Reported-by: Sashiko
Assisted-by: Gemini:gemini-3.1-pro-preview
Link: https://sashiko.dev/#/patchset/20260324161301.1353976-1-tycho%40kernel.org
CC: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Tycho Andersen (AMD) <tycho@xxxxxxxxxx>
---
 drivers/crypto/ccp/sev-dev.c | 33 ++++-----------------------------
 1 file changed, 4 insertions(+), 29 deletions(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index ad6c2525a305..7c4dd57fabb9 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -1727,21 +1727,6 @@ static int sev_move_to_init_state(struct sev_issue_cmd *argp, bool *shutdown_req
 	return 0;
 }
 
-static int snp_move_to_init_state(struct sev_issue_cmd *argp, bool *shutdown_required)
-{
-	int error, rc;
-
-	rc = __sev_snp_init_locked(&error, 0);
-	if (rc) {
-		argp->error = SEV_RET_INVALID_PLATFORM_STATE;
-		return rc;
-	}
-
-	*shutdown_required = true;
-
-	return 0;
-}
-
 static int sev_ioctl_do_reset(struct sev_issue_cmd *argp, bool writable)
 {
 	int state, rc;
@@ -2451,8 +2436,6 @@ static int sev_ioctl_do_snp_set_config(struct sev_issue_cmd *argp, bool writable
 {
 	struct sev_device *sev = psp_master->sev_data;
 	struct sev_user_data_snp_config config;
-	bool shutdown_required = false;
-	int ret, error;
 
 	if (!argp->data)
 		return -EINVAL;
@@ -2460,21 +2443,13 @@ static int sev_ioctl_do_snp_set_config(struct sev_issue_cmd *argp, bool writable
 	if (!writable)
 		return -EPERM;
 
+	if (!sev->snp_initialized)
+		return -ENODEV;
+
 	if (copy_from_user(&config, (void __user *)argp->data, sizeof(config)))
 		return -EFAULT;
 
-	if (!sev->snp_initialized) {
-		ret = snp_move_to_init_state(argp, &shutdown_required);
-		if (ret)
-			return ret;
-	}
-
-	ret = __sev_do_cmd_locked(SEV_CMD_SNP_CONFIG, &config, &argp->error);
-
-	if (shutdown_required)
-		__sev_snp_shutdown_locked(&error, false);
-
-	return ret;
+	return __sev_do_cmd_locked(SEV_CMD_SNP_CONFIG, &config, &argp->error);
 }
 
 static int sev_ioctl_do_snp_vlek_load(struct sev_issue_cmd *argp, bool writable)
-- 
2.54.0