[PATCH v3 6/7] ima: configure memory to log events between kexec load and execute

[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_MEMORY_KB, to configure the
extra memory (in kb) 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..8792b7aab768 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_MEMORY_KB
+	int
+	depends on IMA && IMA_KEXEC
+	default 64
+	help
+	  IMA_KEXEC_EXTRA_MEMORY_KB determines the extra memory to be
+	  allocated (in kb) 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 55bd5362262e..063da9c834a0 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -128,15 +128,18 @@ 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_MEMORY_KB * 1024);
+
 	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