[PATCH v4 2/7] kexec: define functions to map and unmap segments

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

Implement kimage_map_segment() to enable mapping of IMA buffer source
pages to the kimage structure post kexec 'load'.  This function,
accepting a kimage pointer, an address, and a size, will gather the
source pages within the specified address range, create an array of page
pointers, and map these to a contiguous virtual address range.  The
function returns the start of this range if successful, or NULL if
unsuccessful.

Implement kimage_unmap_segment() for unmapping segments
using vunmap().  Relocate 'for_each_kimage_entry()' macro from
kexec_core.c to kexec.h for broader accessibility.

Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
---
 include/linux/kexec.h              | 13 +++++++
 kernel/kexec_core.c                | 59 +++++++++++++++++++++++++++---
 security/integrity/ima/ima_kexec.c |  1 +
 3 files changed, 68 insertions(+), 5 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 22b5cd24f581..e00b8101b53b 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -490,6 +490,15 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g
 static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }
 #endif
 
+#define for_each_kimage_entry(image, ptr, entry) \
+	for (ptr = &image->head; (entry = *ptr) && !(entry & IND_DONE); \
+		ptr = (entry & IND_INDIRECTION) ? \
+			boot_phys_to_virt((entry & PAGE_MASK)) : ptr + 1)
+
+extern void *kimage_map_segment(struct kimage *image,
+				unsigned long addr, unsigned long size);
+extern void kimage_unmap_segment(void *buffer);
+
 #else /* !CONFIG_KEXEC_CORE */
 struct pt_regs;
 struct task_struct;
@@ -497,6 +506,10 @@ static inline void __crash_kexec(struct pt_regs *regs) { }
 static inline void crash_kexec(struct pt_regs *regs) { }
 static inline int kexec_should_crash(struct task_struct *p) { return 0; }
 static inline int kexec_crash_loaded(void) { return 0; }
+static inline void *kimage_map_segment(struct kimage *image,
+				       unsigned long addr, unsigned long size)
+{ return NULL; }
+static inline void kimage_unmap_segment(void *buffer) { }
 #define kexec_in_progress false
 #endif /* CONFIG_KEXEC_CORE */
 
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 3d578c6fefee..26978ad02676 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -594,11 +594,6 @@ void kimage_terminate(struct kimage *image)
 	*image->entry = IND_DONE;
 }
 
-#define for_each_kimage_entry(image, ptr, entry) \
-	for (ptr = &image->head; (entry = *ptr) && !(entry & IND_DONE); \
-		ptr = (entry & IND_INDIRECTION) ? \
-			boot_phys_to_virt((entry & PAGE_MASK)) : ptr + 1)
-
 static void kimage_free_entry(kimage_entry_t entry)
 {
 	struct page *page;
@@ -921,6 +916,60 @@ int kimage_load_segment(struct kimage *image,
 	return result;
 }
 
+void *kimage_map_segment(struct kimage *image,
+			 unsigned long addr, unsigned long size)
+{
+	unsigned long eaddr = addr + size;
+	unsigned long src_page_addr, dest_page_addr;
+	unsigned int npages;
+	struct page **src_pages;
+	int i;
+	kimage_entry_t *ptr, entry;
+	void *vaddr = NULL;
+
+	/*
+	 * Collect the source pages and map them in a contiguous VA range.
+	 */
+	npages = PFN_UP(eaddr) - PFN_DOWN(addr);
+	src_pages = kmalloc_array(npages, sizeof(*src_pages), GFP_KERNEL);
+	if (!src_pages) {
+		pr_err("%s: Could not allocate ima pages array.\n", __func__);
+		return NULL;
+	}
+
+	i = 0;
+	for_each_kimage_entry(image, ptr, entry) {
+		if (entry & IND_DESTINATION)
+			dest_page_addr = entry & PAGE_MASK;
+		else if (entry & IND_SOURCE) {
+			if (dest_page_addr >= addr && dest_page_addr < eaddr) {
+				src_page_addr = entry & PAGE_MASK;
+				src_pages[i++] =
+					virt_to_page(__va(src_page_addr));
+				if (i == npages)
+					break;
+				dest_page_addr += PAGE_SIZE;
+			}
+		}
+	}
+
+	/* Sanity check. */
+	WARN_ON(i < npages);
+
+	vaddr = vmap(src_pages, npages, VM_MAP, PAGE_KERNEL);
+	kfree(src_pages);
+
+	if (!vaddr)
+		pr_err("%s: Could not map imap buffer.\n", __func__);
+
+	return vaddr;
+}
+
+void kimage_unmap_segment(void *segment_buffer)
+{
+	vunmap(segment_buffer);
+}
+
 struct kexec_load_limit {
 	/* Mutex protects the limit count. */
 	struct mutex mutex;
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 99daac355c70..4f944c9b4168 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -170,6 +170,7 @@ void ima_add_kexec_buffer(struct kimage *image)
 	pr_debug("kexec measurement buffer for the loaded kernel at 0x%lx.\n",
 		 kbuf.mem);
 }
+
 #endif /* IMA_KEXEC */
 
 /*
-- 
2.25.1


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