[RFC v2 14/43] PKRAM: prevent inadvertent use of a stale superblock

[Anthony Yznaga]

When pages have been saved to be preserved by the current boot, set
a magic number on the super block to be validated by the next kernel.

Signed-off-by: Anthony Yznaga <anthony.yzn...@oracle.com>
---
 mm/pkram.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/pkram.c b/mm/pkram.c
index dab6657080bf..8670d1633a9d 100644
--- a/mm/pkram.c
+++ b/mm/pkram.c
@@ -22,6 +22,7 @@
 
 #include "internal.h"
 
+#define PKRAM_MAGIC            0x706B726D
 
 /*
  * Represents a reference to a data page saved to PKRAM.
@@ -112,6 +113,8 @@ struct pkram_region_list {
  * The structure occupies a memory page.
  */
 struct pkram_super_block {
+       __u32   magic;
+
        __u64   node_pfn;               /* first element of the node list */
        __u64   region_list_pfn;
        __u64   nr_regions;
@@ -180,6 +183,11 @@ void __init pkram_reserve(void)
                err = PTR_ERR(pkram_sb);
                goto out;
        }
+       if (pkram_sb->magic != PKRAM_MAGIC) {
+               pr_err("PKRAM: invalid super block\n");
+               err = -EINVAL;
+               goto out;
+       }
        /* An empty pkram_sb is not an error */
        if (!pkram_sb->node_pfn) {
                pkram_sb = NULL;
@@ -993,6 +1001,7 @@ static void __pkram_reboot(void)
         */
        memset(pkram_sb, 0, PAGE_SIZE);
        if (!err && node_pfn) {
+               pkram_sb->magic = PKRAM_MAGIC;
                pkram_sb->node_pfn = node_pfn;
                pkram_sb->region_list_pfn = rl_pfn;
                pkram_sb->nr_regions = nr_regions;
-- 
1.8.3.1