[PATCH v4 6/7] ima: make the kexec extra memory configurable

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

The extra memory allocated for carrying the IMA measurement list across
kexec is hardcoded as half a PAGE.  Make it configurable.

Define a Kconfig option, IMA_KEXEC_EXTRA_MEMORY_KB, to configure the
extra memory (in kb) to be allocated for IMA measurements added during
kexec soft reboot.  Ensure the default value of the option is set such
that extra half a page of memory for additional measurements is allocated
to maintain backwards compatibility.

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     | 11 +++++++++++
 security/integrity/ima/ima_kexec.c | 15 ++++++++++-----
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 60a511c6b583..fc103288852b 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -338,3 +338,14 @@ 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 0
+	help
+	  IMA_KEXEC_EXTRA_MEMORY_KB determines the extra memory to be
+	  allocated (in kb) for IMA measurements added during kexec soft reboot.
+	  If set to the default value, an extra half page of memory for
+	  additional measurements will be allocated to maintain backwards
+	  compatibility.
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index f26b5b342d84..c126aa6494e9 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -121,6 +121,7 @@ void ima_add_kexec_buffer(struct kimage *image)
 				  .buf_min = 0, .buf_max = ULONG_MAX,
 				  .top_down = true };
 	unsigned long binary_runtime_size;
+	unsigned long extra_size;
 
 	/* use more understandable variable names than defined in kbuf */
 	void *kexec_buffer = NULL;
@@ -128,15 +129,19 @@ 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 during kexec.
 	 */
-	binary_runtime_size = ima_get_binary_runtime_size();
+	if (CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB <= 0)
+		extra_size = PAGE_SIZE / 2;
+	else
+		extra_size = CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024;
+	binary_runtime_size = ima_get_binary_runtime_size() + 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");
-- 
2.25.1