crypto: ccp - Do not initialize SNP for ioctl(SNP_CONFIG)

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@vger.kernel.org>
Signed-off-by: Tycho Andersen (AMD) <tycho@kernel.org>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 9fb9267d7636e18a9acf5185d54b8bd5de22210a..14df519ae7eea7f9fc8b5884378e04280e76ea08 100644 (file)
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -1730,21 +1730,6 @@ 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;
@@ -2454,8 +2439,6 @@ 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;
@@ -2463,21 +2446,13 @@ 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)