[PATCH v2 6/7] ima: make the memory for events between kexec load and exec configurable

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

IMA currently allocates half a PAGE_SIZE for the extra events that would
be measured between kexec 'load' and 'execute'.  Depending on the IMA
policy and the system state, that memory may not be sufficient to hold
the extra IMA events measured after kexec 'load'.  The memory
requirements vary from system to system and they should be configurable.

Define a Kconfig option, IMA_KEXEC_EXTRA_PAGES, to configure the number
of extra pages to be allocated for IMA measurements added in the window
from kexec 'load' to kexec 'execute'.

Update ima_add_kexec_buffer() function to allocate memory based on the 
Kconfig option value, rather than the currently hardcoded one.

Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
---
 security/integrity/ima/Kconfig     |  9 +++++++++
 security/integrity/ima/ima_kexec.c | 13 ++++++++-----
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 60a511c6b583..1b55cd2bcb36 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -338,3 +338,12 @@ config IMA_DISABLE_HTABLE
 	default n
 	help
 	   This option disables htable to allow measurement of duplicate records.
+
+config IMA_KEXEC_EXTRA_PAGES
+	int
+	depends on IMA && IMA_KEXEC
+	default 16
+	help
+	  IMA_KEXEC_EXTRA_PAGES determines the number of extra
+	  pages to be allocated for IMA measurements added in the
+	  window from kexec 'load' to kexec 'execute'.
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 13fbbb90319b..6cd5f46a7208 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -150,15 +150,18 @@ void ima_add_kexec_buffer(struct kimage *image)
 	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) +
+			      (CONFIG_IMA_KEXEC_EXTRA_PAGES * PAGE_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");
-- 
2.25.1