ima: make the kexec extra memory configurable

JIRA: https://issues.redhat.com/browse/RHEL-114162

Upstream Status: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

commit 0ad9398
Author: Steven Chen <chenste@linux.microsoft.com>
Date:   Mon Apr 21 15:25:14 2025 -0700

    ima: make the kexec extra memory configurable

    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.

    Suggested-by: Stefan Berger <stefanb@linux.ibm.com>
    Co-developed-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
    Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
    Signed-off-by: Steven Chen <chenste@linux.microsoft.com>
    Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
    Acked-by: Baoquan He <bhe@redhat.com>
    Tested-by: Stefan Berger <stefanb@linux.ibm.com> # ppc64/kvm
    Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

Signed-off-by: Baoquan He <bhe@redhat.com>

Author: Baoquan He

security/integrity/ima/Kconfig

@@ -321,4 +321,15 @@ 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"
+	range 0 40
+	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 of 0, an extra half page of memory for those
+	  additional measurements will be allocated.
+
 endif

security/integrity/ima/ima_kexec.c

@@ -118,22 +118,28 @@ 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_memory;
 
 	/* use more understandable variable names than defined in kbuf */
 	size_t kexec_buffer_size = 0;
 	void *kexec_buffer = NULL;
 	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_memory = PAGE_SIZE / 2;
+	else
+		extra_memory = CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024;
+
+	binary_runtime_size = ima_get_binary_runtime_size() + extra_memory;
+
 	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");