[PATCH v4 05/13] tpm: add cursor based buffer functions for response parsing

From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: linux-integrity@vger.kernel.org
Cc: Jarkko Sakkinen <jarkko@kernel.org>,
	keyrings@vger.kernel.org, Ard Biesheuvel <ardb@kernel.org>
Subject: [PATCH v4 05/13] tpm: add cursor based buffer functions for response parsing
Date: Mon,  3 Apr 2023 17:39:55 -0400	[thread overview]
Message-ID: <20230403214003.32093-6-James.Bottomley@HansenPartnership.com> (raw)
In-Reply-To: <20230403214003.32093-1-James.Bottomley@HansenPartnership.com>

Extracting values from returned TPM buffers can be hard.  Add cursor
based (moving poiner) functions that make it easier to extract TPM
returned values from a buffer.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

---
v4: add kernel doc and reword commit
---
 drivers/char/tpm/tpm-buf.c | 48 ++++++++++++++++++++++++++++++++++++++
 include/linux/tpm.h        |  3 +++
 2 files changed, 51 insertions(+)

diff --git a/drivers/char/tpm/tpm-buf.c b/drivers/char/tpm/tpm-buf.c
index b7e42fb6266c..da0f6e725c3f 100644
--- a/drivers/char/tpm/tpm-buf.c
+++ b/drivers/char/tpm/tpm-buf.c
@@ -6,6 +6,8 @@
 #include <linux/module.h>
 #include <linux/tpm.h>
 
+#include <asm/unaligned.h>
+
 static int __tpm_buf_init(struct tpm_buf *buf)
 {
 	buf->data = (u8 *)__get_free_page(GFP_KERNEL);
@@ -229,3 +231,49 @@ void tpm_buf_append_2b(struct tpm_buf *buf, struct tpm_buf *tpm2b)
 	tpm_buf_reset_int(tpm2b);
 }
 EXPORT_SYMBOL_GPL(tpm_buf_append_2b);
+
+/* functions for unmarshalling data and moving the cursor */
+
+/**
+ * tpm_get_inc_u8 - read a u8 and move pointer beyond it
+ * @ptr: pointer to pointer
+ *
+ * @return: value read
+ */
+u8 tpm_get_inc_u8(const u8 **ptr)
+{
+	return *((*ptr)++);
+}
+EXPORT_SYMBOL_GPL(tpm_get_inc_u8);
+
+/**
+ * tpm_get_inc_u16 - read a u16 and move pointer beyond it
+ * @ptr: pointer to pointer
+ *
+ * @return: value read (converted from big endian)
+ */
+u16 tpm_get_inc_u16(const u8 **ptr)
+{
+	u16 val;
+
+	val = get_unaligned_be16(*ptr);
+	*ptr += sizeof(val);
+	return val;
+}
+EXPORT_SYMBOL_GPL(tpm_get_inc_u16);
+
+/**
+ * tpm_get_inc_u32 - read a u32 and move pointer beyond it
+ * @ptr: pointer to pointer
+ *
+ * @return: value read (converted from big endian)
+ */
+u32 tpm_get_inc_u32(const u8 **ptr)
+{
+	u32 val;
+
+	val = get_unaligned_be32(*ptr);
+	*ptr += sizeof(val);
+	return val;
+}
+EXPORT_SYMBOL_GPL(tpm_get_inc_u32);
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 76d495cb5b08..845eadfed715 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -336,6 +336,9 @@ void tpm_buf_append_u8(struct tpm_buf *buf, const u8 value);
 void tpm_buf_append_u16(struct tpm_buf *buf, const u16 value);
 void tpm_buf_append_u32(struct tpm_buf *buf, const u32 value);
 void tpm_buf_append_2b(struct tpm_buf *buf, struct tpm_buf *tpm2b);
+u8 tpm_get_inc_u8(const u8 **ptr);
+u16 tpm_get_inc_u16(const u8 **ptr);
+u32 tpm_get_inc_u32(const u8 **ptr);
 
 /*
  * Check if TPM device is in the firmware upgrade mode.
-- 
2.35.3

