[tip:x86/boot] x86/KASLR: Return earliest overlap when avoiding regions

[tip-bot for Kees Cook]

Commit-ID:  06486d6c97cebc2433a40a979f3849cd68184de9
Gitweb:     http://git.kernel.org/tip/06486d6c97cebc2433a40a979f3849cd68184de9
Author:     Kees Cook <keescook@xxxxxxxxxxxx>
AuthorDate: Mon, 9 May 2016 13:22:07 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 10 May 2016 10:12:04 +0200

x86/KASLR: Return earliest overlap when avoiding regions

In preparation for being able to detect where to split up contiguous
memory regions that overlap with memory regions to avoid, we need to
pass back what the earliest overlapping region was. This modifies the
overlap checker to return that information.

Based on a separate mem_min_overlap() implementation by Baoquan He.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
Cc: kernel-hardening@xxxxxxxxxxxxxxxxxx
Cc: lasse.collin@xxxxxxxxxxx
Link: http://lkml.kernel.org/r/1462825332-10505-5-git-send-email-keescook@xxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/boot/compressed/kaslr.c | 29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 81edf99..e55ebcb 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -279,15 +279,24 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
 #endif
 }
 
-/* Does this memory vector overlap a known avoided area? */
-static bool mem_avoid_overlap(struct mem_vector *img)
+/*
+ * Does this memory vector overlap a known avoided area? If so, record the
+ * overlap region with the lowest address.
+ */
+static bool mem_avoid_overlap(struct mem_vector *img,
+			      struct mem_vector *overlap)
 {
 	int i;
 	struct setup_data *ptr;
+	unsigned long earliest = img->start + img->size;
+	bool is_overlapping = false;
 
 	for (i = 0; i < MEM_AVOID_MAX; i++) {
-		if (mem_overlaps(img, &mem_avoid[i]))
-			return true;
+		if (mem_overlaps(img, &mem_avoid[i]) &&
+		    mem_avoid[i].start < earliest) {
+			*overlap = mem_avoid[i];
+			is_overlapping = true;
+		}
 	}
 
 	/* Avoid all entries in the setup_data linked list. */
@@ -298,13 +307,15 @@ static bool mem_avoid_overlap(struct mem_vector *img)
 		avoid.start = (unsigned long)ptr;
 		avoid.size = sizeof(*ptr) + ptr->len;
 
-		if (mem_overlaps(img, &avoid))
-			return true;
+		if (mem_overlaps(img, &avoid) && (avoid.start < earliest)) {
+			*overlap = avoid;
+			is_overlapping = true;
+		}
 
 		ptr = (struct setup_data *)(unsigned long)ptr->next;
 	}
 
-	return false;
+	return is_overlapping;
 }
 
 static unsigned long slots[KERNEL_IMAGE_SIZE / CONFIG_PHYSICAL_ALIGN];
@@ -361,7 +372,7 @@ static void process_e820_entry(struct e820entry *entry,
 			       unsigned long minimum,
 			       unsigned long image_size)
 {
-	struct mem_vector region, img;
+	struct mem_vector region, img, overlap;
 
 	/* Skip non-RAM entries. */
 	if (entry->type != E820_RAM)
@@ -400,7 +411,7 @@ static void process_e820_entry(struct e820entry *entry,
 	for (img.start = region.start, img.size = image_size ;
 	     mem_contains(&region, &img) ;
 	     img.start += CONFIG_PHYSICAL_ALIGN) {
-		if (mem_avoid_overlap(&img))
+		if (mem_avoid_overlap(&img, &overlap))
 			continue;
 		slots_append(img.start);
 	}