[PATCH v3] crypto: ccp: Fix SNP panic notifier unregistration

[PATCH v3] crypto: ccp: Fix SNP panic notifier unregistration

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@amd.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.

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Fixes: 19860c3274fb ("crypto: ccp - Register SNP panic notifier only if SNP is enabled")
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---
 drivers/crypto/ccp/sev-dev.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 8fb94c5f006a..17edc6bf5622 100644
--- 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;
-- 
2.34.1

Re: [PATCH v3] crypto: ccp: Fix SNP panic notifier unregistration

[kernel test robot]

Hi,

Thanks for your patch.

FYI: kernel test robot notices the stable kernel rule is not satisfied.

The check is based on https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html#option-1

Rule: add the tag "Cc: stable@vger.kernel.org" in the sign-off area to have the patch automatically included in the stable tree.
Subject: [PATCH v3] crypto: ccp: Fix SNP panic notifier unregistration
Link: https://lore.kernel.org/stable/20250616214314.68518-1-Ashish.Kalra%40amd.com

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