proc/kcore: don't bounds check against address 0

The existing kcore code checks for bad addresses against __va(0) with
the assumption that this is the lowest address on the system.  This may
not hold true on some systems (e.g.  arm64) and produce overflows and
crashes.  Switch to using other functions to validate the address range.

It's currently only seen on arm64 and it's not clear if anyone wants to
use that particular combination on a stable release.  So this is not
urgent for stable.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Laura Abbott <[email protected]>
Tested-by: Dave Anderson <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Alexey Dobriyan <[email protected]>a
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 16 insertions, 7 deletions

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index d1e82761de81..e64ecb9f2720 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -209,25 +209,34 @@ kclist_add_private(unsigned long pfn, unsigned long nr_pages, void *arg)
 {
 	struct list_head *head = (struct list_head *)arg;
 	struct kcore_list *ent;
+	struct page *p;
+
+	if (!pfn_valid(pfn))
+		return 1;
+
+	p = pfn_to_page(pfn);
+	if (!memmap_valid_within(pfn, p, page_zone(p)))
+		return 1;
 
 	ent = kmalloc(sizeof(*ent), GFP_KERNEL);
 	if (!ent)
 		return -ENOMEM;
-	ent->addr = (unsigned long)__va((pfn << PAGE_SHIFT));
+	ent->addr = (unsigned long)page_to_virt(p);
 	ent->size = nr_pages << PAGE_SHIFT;
 
-	/* Sanity check: Can happen in 32bit arch...maybe */
-	if (ent->addr < (unsigned long) __va(0))
+	if (!virt_addr_valid(ent->addr))
 		goto free_out;
 
 	/* cut not-mapped area. ....from ppc-32 code. */
 	if (ULONG_MAX - ent->addr < ent->size)
 		ent->size = ULONG_MAX - ent->addr;
 
-	/* cut when vmalloc() area is higher than direct-map area */
-	if (VMALLOC_START > (unsigned long)__va(0)) {
-		if (ent->addr > VMALLOC_START)
-			goto free_out;
+	/*
+	 * We've already checked virt_addr_valid so we know this address
+	 * is a valid pointer, therefore we can check against it to determine
+	 * if we need to trim
+	 */
+	if (VMALLOC_START > ent->addr) {
 		if (VMALLOC_START - ent->addr < ent->size)
 			ent->size = VMALLOC_START - ent->addr;
 	}