[S390] kdump: Add infrastructure for unmapping crashkernel memory

This patch introduces a mechanism that allows architecture backends to
remove page tables for the crashkernel memory. This can protect the loaded
kdump kernel from being overwritten by broken kernel code.  Two new
functions crash_map_reserved_pages() and crash_unmap_reserved_pages() are
added that can be implemented by architecture code.  The
crash_map_reserved_pages() function is called before and
crash_unmap_reserved_pages() after the crashkernel segments are loaded.  The
functions are also called in crash_shrink_memory() to create/remove page
tables when the crashkernel memory size is reduced.

To support architectures that have large pages this patch also introduces
a new define KEXEC_CRASH_MEM_ALIGN. The crashkernel start and size must
always be aligned with KEXEC_CRASH_MEM_ALIGN.

Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 19 insertions, 2 deletions

diff --git a/kernel/kexec.c b/kernel/kexec.c
index d3b8a4ceb90b..dc7bc0829286 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -999,6 +999,7 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
                         kimage_free(xchg(&kexec_crash_image, NULL));
                         result = kimage_crash_alloc(&image, entry,
                                                      nr_segments, segments);
+                        crash_map_reserved_pages();
                 }
                 if (result)
                         goto out;
@@ -1015,6 +1016,8 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
                                 goto out;
                 }
                 kimage_terminate(image);
+                if (flags & KEXEC_ON_CRASH)
+                        crash_unmap_reserved_pages();
         }
         /* Install the new kernel, and  Uninstall the old */
         image = xchg(dest_image, image);
@@ -1026,6 +1029,18 @@ out:
         return result;
 }
 
+/*
+ * Add and remove page tables for crashkernel memory
+ *
+ * Provide an empty default implementation here -- architecture
+ * code may override this
+ */
+void __weak crash_map_reserved_pages(void)
+{}
+
+void __weak crash_unmap_reserved_pages(void)
+{}
+
 #ifdef CONFIG_COMPAT
 asmlinkage long compat_sys_kexec_load(unsigned long entry,
                                 unsigned long nr_segments,
@@ -1134,14 +1149,16 @@ int crash_shrink_memory(unsigned long new_size)
                 goto unlock;
         }
 
-        start = roundup(start, PAGE_SIZE);
-        end = roundup(start + new_size, PAGE_SIZE);
+        start = roundup(start, KEXEC_CRASH_MEM_ALIGN);
+        end = roundup(start + new_size, KEXEC_CRASH_MEM_ALIGN);
 
+        crash_map_reserved_pages();
         crash_free_reserved_phys_range(end, crashk_res.end);
 
         if ((start == end) && (crashk_res.parent != NULL))
                 release_resource(&crashk_res);
         crashk_res.end = end - 1;
+        crash_unmap_reserved_pages();
 
 unlock:
         mutex_unlock(&kexec_mutex);