kexec: define functions to map and unmap segments

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

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

commit 0091d92
Author: Steven Chen <chenste@linux.microsoft.com>
Date:   Mon Apr 21 15:25:09 2025 -0700

    kexec: define functions to map and unmap segments

    Implement kimage_map_segment() to enable IMA to map the measurement log
    list to the kimage structure during the kexec 'load' stage. This function
    gathers the source pages within the specified address range, and maps them
    to a contiguous virtual address range.

    This is a preparation for later usage.

    Implement kimage_unmap_segment() for unmapping segments using vunmap().

    Cc: Eric Biederman <ebiederm@xmission.com>
    Cc: Baoquan He <bhe@redhat.com>
    Cc: Vivek Goyal <vgoyal@redhat.com>
    Cc: Dave Young <dyoung@redhat.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>
    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

include/linux/kexec.h

@@ -474,13 +474,19 @@ extern bool kexec_file_dbg_print;
 #define kexec_dprintk(fmt, arg...) \
         do { if (kexec_file_dbg_print) pr_info(fmt, ##arg); } while (0)
 
+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;
+struct kimage;
 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 */
 

kernel/kexec_core.c

@@ -877,6 +877,60 @@ int kimage_load_segment(struct kimage *image,
 	return result;
 }
 
+void *kimage_map_segment(struct kimage *image,
+			 unsigned long addr, unsigned long size)
+{
+	unsigned long src_page_addr, dest_page_addr = 0;
+	unsigned long eaddr = addr + size;
+	kimage_entry_t *ptr, entry;
+	struct page **src_pages;
+	unsigned int npages;
+	void *vaddr = NULL;
+	int i;
+
+	/*
+	 * 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("Could not allocate ima pages array.\n");
+		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("Could not map ima buffer.\n");
+
+	return vaddr;
+}
+
+void kimage_unmap_segment(void *segment_buffer)
+{
+	vunmap(segment_buffer);
+}
+
 struct kexec_load_limit {
 	/* Mutex protects the limit count. */
 	struct mutex mutex;