tpm-buf: Memory-safe allocations

Decouple kzalloc from buffer creation, so that a managed allocation can be
used:

	struct tpm_buf *buf __free(kfree) buf = kzalloc(TPM_BUFSIZE,
						GFP_KERNEL);
	if (!buf)
		return -ENOMEM;

	tpm_buf_init(buf, TPM_BUFSIZE);

Alternatively, other allocations are also possible (static data, stack,
etc) for example:

	u8 buf_data[512];
	struct tpm_buf *buf = (struct tpm_buf *)buf_data;
	tpm_buf_init(buf, sizeof(buf_data));

This is achieved by embedding buffer's header inside the allocated blob,
instead of having an outer wrapper.

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@opinsys.com>
Tested-by: Srish Srinivasan <ssrish@linux.ibm.com>
Message-ID: <20260522013555.1063716-1-jarkko@kernel.org>
Signed-off-by: Ross Philipson <ross.philipson@oracle.com>

1 files changed, 9 insertions, 8 deletions

diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index b357f8971d03..598dd53a10d8 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -208,13 +208,15 @@ enum tpm_buf_flags {
 };
 
 /*
- * A string buffer type for constructing TPM commands.
+ * A buffer for constructing and parsing TPM commands, responses and sized
+ * (TPM2B) buffers.
  */
 struct tpm_buf {
-	u32 flags;
-	u32 length;
-	u8 *data;
+	u8 flags;
+	u16 length;
+	u16 capacity;
 	u8 handles;
+	u8 data[];
 };
 
 struct tpm2_hash {
@@ -222,12 +224,11 @@ struct tpm2_hash {
 	unsigned int tpm_id;
 };
 
-int tpm_buf_init(struct tpm_buf *buf, u16 tag, u32 ordinal);
+void tpm_buf_init(struct tpm_buf *buf, u16 buf_size);
+void tpm_buf_init_sized(struct tpm_buf *buf, u16 buf_size);
 void tpm_buf_reset(struct tpm_buf *buf, u16 tag, u32 ordinal);
-int tpm_buf_init_sized(struct tpm_buf *buf);
 void tpm_buf_reset_sized(struct tpm_buf *buf);
-void tpm_buf_destroy(struct tpm_buf *buf);
-u32 tpm_buf_length(struct tpm_buf *buf);
+u16 tpm_buf_length(struct tpm_buf *buf);
 void tpm_buf_append(struct tpm_buf *buf, const u8 *new_data, u16 new_length);
 void tpm_buf_append_u8(struct tpm_buf *buf, const u8 value);
 void tpm_buf_append_u16(struct tpm_buf *buf, const u16 value);