[PATCH v7 6/7] ima: make the kexec extra memory configurable

[steven chen <chenste@linux.microsoft.com>]

The extra memory allocated for carrying the IMA measurement list across
kexec is hard-coded 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
for the additional measurements.

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

From: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Author: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Suggested-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Signed-off-by: steven chen <chenste@linux.microsoft.com>
---
 security/integrity/ima/Kconfig     | 10 ++++++++++
 security/integrity/ima/ima_kexec.c | 16 ++++++++++------
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 475c32615006..54b145ae6096 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -321,4 +321,14 @@ config IMA_DISABLE_HTABLE
 	help
 	   This option disables htable to allow measurement of duplicate records.
 
+config IMA_KEXEC_EXTRA_MEMORY_KB
+	int "Extra memory for IMA measurements added during kexec soft reboot"
+	depends on 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 a page of memory for those
+	  additional measurements will be allocated.
+
 endif
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index d5f004cfeaec..c9c916f69ca7 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -128,22 +128,26 @@ 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;
 	size_t kexec_buffer_size = 0;
 	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