x86/amd_node: Fix PCI device reference counting in amd_smn_init()grafted

The local "root" pointer is a temporary variable used during the device
search. Therefore, refcount related to the search iterators should be cleaned
up after the search is complete.

Use the __free() cleanup macro to ensure the refcount is decremented when the
temporary pointer goes out of scope.

Additionally, increment the refcount when caching a root pointer. This ensures
the in-use refcount is separate from the temporary search refcounting.

Finally, drop the redundant "root = NULL" before the second search loop. The
pci_get_class() iterator always decrements the refcount of its "from"
argument, so the first loop can only fall through with "root" already NULL.

Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com
Reported-by: Sashiko <sashiko-bot@kernel.org>
Assisted-by: LLM
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com

1 files changed, 51 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/securityfs-secrets-coco b/Documentation/ABI/testing/securityfs-secrets-coco
new file mode 100644
index 000000000..f2b690915
--- /dev/null
+++ b/Documentation/ABI/testing/securityfs-secrets-coco
@@ -0,0 +1,51 @@
+What:		security/secrets/coco
+Date:		February 2022
+Contact:	Dov Murik <dovmurik@linux.ibm.com>
+Description:
+		Exposes confidential computing (coco) EFI secrets to
+		userspace via securityfs.
+
+		EFI can declare memory area used by confidential computing
+		platforms (such as AMD SEV and SEV-ES) for secret injection by
+		the Guest Owner during VM's launch.  The secrets are encrypted
+		by the Guest Owner and decrypted inside the trusted enclave,
+		and therefore are not readable by the untrusted host.
+
+		The efi_secret module exposes the secrets to userspace.  Each
+		secret appears as a file under <securityfs>/secrets/coco,
+		where the filename is the GUID of the entry in the secrets
+		table.  This module is loaded automatically by the EFI driver
+		if the EFI secret area is populated.
+
+		Two operations are supported for the files: read and unlink.
+		Reading the file returns the content of secret entry.
+		Unlinking the file overwrites the secret data with zeroes and
+		removes the entry from the filesystem.  A secret cannot be read
+		after it has been unlinked.
+
+		For example, listing the available secrets::
+
+		  # modprobe efi_secret
+		  # ls -l /sys/kernel/security/secrets/coco
+		  -r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b
+		  -r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6
+		  -r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2
+		  -r--r----- 1 root root 0 Jun 28 11:54 e6f5a162-d67f-4750-a67c-5d065f2a9910
+
+		Reading the secret data by reading a file::
+
+		  # cat /sys/kernel/security/secrets/coco/e6f5a162-d67f-4750-a67c-5d065f2a9910
+		  the-content-of-the-secret-data
+
+		Wiping a secret by unlinking a file::
+
+		  # rm /sys/kernel/security/secrets/coco/e6f5a162-d67f-4750-a67c-5d065f2a9910
+		  # ls -l /sys/kernel/security/secrets/coco
+		  -r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b
+		  -r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6
+		  -r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2
+
+		Note: The binary format of the secrets table injected by the
+		Guest Owner is described in
+		drivers/virt/coco/efi_secret/efi_secret.c under "Structure of
+		the EFI secret area".