[PATCH 03/10] ima: allocate buffer at kexec load to hold ima measurements

[Tushar Sugandhi <tusharsu@linux.microsoft.com>]

The IMA subsystem needs a dedicated mechanism to reserve extra memory for
measurements added between the kexec 'load' and kexec 'execute'.

Update ima_add_kexec_buffer to allocate a buffer of a sufficient size
taking ima binary runtime measurements size, size of ima_kexec_hdr, and
IMA_KEXEC_EXTRA_SIZE into account.  Adjust the kexec_segment_size to align
to the PAGE_SIZE.  Call ima_allocate_buf_at_kexec_load() to allocate the
buffer.

This patch assumes the extra space defined (IMA_KEXEC_EXTRA_SIZE) is
sufficient to handle the additional measurements.  This should be as per
the system requirements and based on the number of additional measurements
expected during the window from kexec 'load' to kexec 'execute'.

Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
---
 security/integrity/ima/ima.h       |  2 ++
 security/integrity/ima/ima_kexec.c | 21 ++++++++++-----------
 2 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index c29db699c996..2ffda9449b9b 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -43,6 +43,8 @@ enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8, TPM_PCR10 = 10 };
 
 #define NR_BANKS(chip) ((chip != NULL) ? chip->nr_allocated_banks : 0)
 
+#define IMA_KEXEC_EXTRA_SIZE (16 * PAGE_SIZE)
+
 /* current content of the policy */
 extern int ima_policy_flag;
 
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 858b67689701..7deb8df31485 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -188,31 +188,30 @@ void ima_add_kexec_buffer(struct kimage *image)
 	/* use more understandable variable names than defined in kbuf */
 	void *kexec_buffer = NULL;
 	size_t kexec_buffer_size;
-	size_t kexec_segment_size;
 	int ret;
 
 	/*
-	 * Reserve an extra half page of memory for additional measurements
-	 * added during the kexec load.
+	 * Reserve extra memory for measurements added in the window from
+	 * kexec 'load' to kexec 'execute'.
 	 */
-	binary_runtime_size = ima_get_binary_runtime_size();
+	binary_runtime_size = ima_get_binary_runtime_size() +
+			      sizeof(struct ima_kexec_hdr) +
+			      IMA_KEXEC_EXTRA_SIZE;
+
 	if (binary_runtime_size >= ULONG_MAX - PAGE_SIZE)
 		kexec_segment_size = ULONG_MAX;
 	else
-		kexec_segment_size = ALIGN(ima_get_binary_runtime_size() +
-					   PAGE_SIZE / 2, PAGE_SIZE);
+		kexec_segment_size = ALIGN(binary_runtime_size, PAGE_SIZE);
+
 	if ((kexec_segment_size == ULONG_MAX) ||
 	    ((kexec_segment_size >> PAGE_SHIFT) > totalram_pages() / 2)) {
 		pr_err("Binary measurement list too large.\n");
 		return;
 	}
 
-	ima_dump_measurement_list(&kexec_buffer_size, &kexec_buffer,
-				  kexec_segment_size);
-	if (!kexec_buffer) {
-		pr_err("Not enough memory for the kexec measurement buffer.\n");
+	ret = ima_allocate_buf_at_kexec_load();
+	if (ret < 0)
 		return;
-	}
 
 	kbuf.buffer = kexec_buffer;
 	kbuf.bufsz = kexec_buffer_size;
-- 
2.25.1