linux-kernel - [PATCH v2] crypto: ccp: Fix SNP panic notifier unregistration

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Message-ID: <20250605203803.4688-1-Ashish.Kalra@amd.com>
Date: Thu, 5 Jun 2025 20:38:03 +0000
From: Ashish Kalra <Ashish.Kalra@....com>
To: <thomas.lendacky@....com>, <john.allen@....com>,
	<herbert@...dor.apana.org.au>, <davem@...emloft.net>
CC: <aik@....com>, <dionnaglaze@...gle.com>, <michael.roth@....com>,
	<linux-crypto@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] crypto: ccp: Fix SNP panic notifier unregistration

From: Ashish Kalra <ashish.kalra@....com>

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.

Fixes: 19860c3274fb ("crypto: ccp - Register SNP panic notifier only if SNP is enabled")
Signed-off-by: Ashish Kalra <ashish.kalra@....com>
---
 drivers/crypto/ccp/sev-dev.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 8fb94c5f006a..0ba5fe3b7883 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -1787,8 +1787,9 @@ 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);
+	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;
-- 
2.34.1