crypto: ccp - Fix SNP panic notifier unregistration

commit ab8b9fd39c45b7760093528cbef93e7353359d82 upstream.

Panic notifiers are invoked with RCU read lock held and when the
SNP panic notifier tries to unregister itself from the panic
notifier callback itself it causes a deadlock as notifier
unregistration does RCU synchronization.

Code flow for SNP panic notifier:
snp_shutdown_on_panic() ->
__sev_firmware_shutdown() ->
__sev_snp_shutdown_locked() ->
atomic_notifier_chain_unregister(.., &snp_panic_notifier)

Fix SNP panic notifier to unregister itself during SNP shutdown
only if panic is not in progress.

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: stable@vger.kernel.org
Fixes: 19860c3274fb ("crypto: ccp - Register SNP panic notifier only if SNP is enabled")
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 539c303beb3a28088ce6c1d1b0981ad1ab3dbee3..e058ba0277929620c14618e43ba7e89e05f981d2 100644 (file)
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -1787,8 +1787,14 @@ static int __sev_snp_shutdown_locked(int *error, bool panic)
        sev->snp_initialized = false;
        dev_dbg(sev->dev, "SEV-SNP firmware shutdown\n");
 
-       atomic_notifier_chain_unregister(&panic_notifier_list,
-                                        &snp_panic_notifier);
+       /*
+        * __sev_snp_shutdown_locked() deadlocks when it tries to unregister
+        * itself during panic as the panic notifier is called with RCU read
+        * lock held and notifier unregistration does RCU synchronization.
+        */
+       if (!panic)
+               atomic_notifier_chain_unregister(&panic_notifier_list,
+                                                &snp_panic_notifier);
 
        /* Reset TMR size back to default */
        sev_es_tmr_size = SEV_TMR_SIZE;