[RFC v2 14/26] mm/asi: Handle ASI mapped range leaks and overlaps

[Alexandre Chartre]

When mapping a buffer in an ASI page-table, data around the buffer can
also be mapped if the entire buffer is not aligned with the page directory
size used for the mapping. So, data can potentially leak into the ASI
page-table. In such a case, print a warning that data are leaking.

Also data effectively mapped can overlap with an already mapped buffer.
This is not an issue when mapping data but, when unmapping, make sure
data from another buffer don't get unmapped as a side effect.

Signed-off-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
---
 arch/x86/mm/asi_pagetable.c |  230 +++++++++++++++++++++++++++++++++++++++----
 1 files changed, 212 insertions(+), 18 deletions(-)

diff --git a/arch/x86/mm/asi_pagetable.c b/arch/x86/mm/asi_pagetable.c
index 1ff0c47..f1ee65b 100644
--- a/arch/x86/mm/asi_pagetable.c
+++ b/arch/x86/mm/asi_pagetable.c
@@ -9,6 +9,14 @@
 
 #include <asm/asi.h>
 
+static unsigned long page_directory_size[] = {
+	[PGT_LEVEL_PTE] = PAGE_SIZE,
+	[PGT_LEVEL_PMD] = PMD_SIZE,
+	[PGT_LEVEL_PUD] = PUD_SIZE,
+	[PGT_LEVEL_P4D] = P4D_SIZE,
+	[PGT_LEVEL_PGD] = PGDIR_SIZE,
+};
+
 /*
  * Structure to keep track of address ranges mapped into an ASI.
  */
@@ -17,8 +25,16 @@ struct asi_range_mapping {
 	void *ptr;			/* range start address */
 	size_t size;			/* range size */
 	enum page_table_level level;	/* mapping level */
+	int overlap;			/* overlap count */
 };
 
+#define ASI_RANGE_MAP_ADDR(r)	\
+	round_down((unsigned long)((r)->ptr), page_directory_size[(r)->level])
+
+#define ASI_RANGE_MAP_END(r)	\
+	round_up((unsigned long)((r)->ptr + (r)->size), \
+		 page_directory_size[(r)->level])
+
 /*
  * Get the pointer to the beginning of a page table directory from a page
  * table directory entry.
@@ -609,6 +625,71 @@ static int asi_copy_pgd_range(struct asi *asi,
 	return 0;
 }
 
+
+/*
+ * Map a VA range, taking into account any overlap with already mapped
+ * VA ranges. On error, return < 0. Otherwise return the number of
+ * ranges the specified range is overlapping with.
+ */
+static int asi_map_overlap(struct asi *asi, void *ptr, size_t size,
+			   enum page_table_level level)
+{
+	unsigned long map_addr, map_end;
+	unsigned long addr, end;
+	struct asi_range_mapping *range;
+	bool need_mapping;
+	int err, overlap;
+
+	addr = (unsigned long)ptr;
+	end = addr + (unsigned long)size;
+	need_mapping = true;
+	overlap = 0;
+
+	lockdep_assert_held(&asi->lock);
+	list_for_each_entry(range, &asi->mapping_list, list) {
+
+		if (range->ptr == ptr && range->size == size) {
+			/* we are mapping the same range again */
+			pr_debug("ASI %p: MAP %px/%lx/%d already mapped\n",
+				 asi, ptr, size, level);
+			return -EBUSY;
+		}
+
+		/* check overlap with mapped range */
+		map_addr = ASI_RANGE_MAP_ADDR(range);
+		map_end = ASI_RANGE_MAP_END(range);
+		if (end <= map_addr || addr >= map_end) {
+			/* no overlap, continue */
+			continue;
+		}
+
+		pr_debug("ASI %p: MAP %px/%lx/%d overlaps with %px/%lx/%d\n",
+			 asi, ptr, size, level,
+			 range->ptr, range->size, range->level);
+		range->overlap++;
+		overlap++;
+
+		/*
+		 * Check if new range is included into an existing range.
+		 * If so then the new range is already entirely mapped.
+		 */
+		if (addr >= map_addr && end <= map_end) {
+			pr_debug("ASI %p: MAP %px/%lx/%d implicitly mapped\n",
+				 asi, ptr, size, level);
+			need_mapping = false;
+		}
+	}
+
+	if (need_mapping) {
+		err = asi_copy_pgd_range(asi, asi->pgd, current->mm->pgd,
+					 addr, end, level);
+		if (err)
+			return err;
+	}
+
+	return overlap;
+}
+
 /*
  * Copy page table entries from the current page table (i.e. from the
  * kernel page table) to the specified ASI page-table. The level
@@ -619,44 +700,53 @@ int asi_map_range(struct asi *asi, void *ptr, size_t size,
 		  enum page_table_level level)
 {
 	struct asi_range_mapping *range_mapping;
+	unsigned long page_dir_size = page_directory_size[level];
 	unsigned long addr = (unsigned long)ptr;
 	unsigned long end = addr + ((unsigned long)size);
+	unsigned long map_addr, map_end;
 	unsigned long flags;
-	int err;
+	int err, overlap;
+
+	map_addr = round_down(addr, page_dir_size);
+	map_end = round_up(end, page_dir_size);
 
-	pr_debug("ASI %p: MAP %px/%lx/%d\n", asi, ptr, size, level);
+	pr_debug("ASI %p: MAP %px/%lx/%d -> %lx-%lx\n", asi, ptr, size, level,
+		 map_addr, map_end);
+	if (map_addr < addr)
+		pr_debug("ASI %p: MAP LEAK %lx-%lx\n", asi, map_addr, addr);
+	if (map_end > end)
+		pr_debug("ASI %p: MAP LEAK %lx-%lx\n", asi, end, map_end);
 
 	spin_lock_irqsave(&asi->lock, flags);
 
-	/* check if the range is already mapped */
-	range_mapping = asi_get_range_mapping(asi, ptr);
-	if (range_mapping) {
-		pr_debug("ASI %p: MAP %px/%lx/%d already mapped\n",
-			 asi, ptr, size, level);
-		err = -EBUSY;
-		goto done;
+	/*
+	 * Map the new range with taking overlap with already mapped ranges
+	 * into account.
+	 */
+	overlap = asi_map_overlap(asi, ptr, size, level);
+	if (overlap < 0) {
+		err = overlap;
+		goto error;
 	}
 
-	/* map new range */
+	/* add new range */
 	range_mapping = kmalloc(sizeof(*range_mapping), GFP_KERNEL);
 	if (!range_mapping) {
 		err = -ENOMEM;
-		goto done;
+		goto error;
 	}
 
-	err = asi_copy_pgd_range(asi, asi->pgd, current->mm->pgd,
-				 addr, end, level);
-	if (err)
-		goto done;
-
 	INIT_LIST_HEAD(&range_mapping->list);
 	range_mapping->ptr = ptr;
 	range_mapping->size = size;
 	range_mapping->level = level;
+	range_mapping->overlap = overlap;
 	list_add(&range_mapping->list, &asi->mapping_list);
-done:
 	spin_unlock_irqrestore(&asi->lock, flags);
+	return 0;
 
+error:
+	spin_unlock_irqrestore(&asi->lock, flags);
 	return err;
 }
 EXPORT_SYMBOL(asi_map_range);
@@ -776,6 +866,110 @@ static void asi_clear_pgd_range(struct asi *asi, pgd_t *pagetable,
 	} while (pgd++, addr = next, addr < end);
 }
 
+
+/*
+ * Unmap a VA range, taking into account any overlap with other mapped
+ * VA ranges. This unmaps the specified range then remap any range this
+ * range was overlapping with.
+ */
+static void asi_unmap_overlap(struct asi *asi, struct asi_range_mapping *range)
+{
+	unsigned long map_addr, map_end;
+	struct asi_range_mapping *r;
+	unsigned long addr, end;
+	unsigned long r_addr;
+	bool need_unmapping;
+	int err, overlap;
+
+	addr = (unsigned long)range->ptr;
+	end = addr + (unsigned long)range->size;
+	overlap = range->overlap;
+	need_unmapping = true;
+
+	lockdep_assert_held(&asi->lock);
+
+	/*
+	 * Adjust overlap information and check if range effectively needs
+	 * to be unmapped.
+	 */
+	list_for_each_entry(r, &asi->mapping_list, list) {
+
+		if (!overlap) {
+			/* no more overlap */
+			break;
+		}
+
+		WARN_ON(range->ptr == r->ptr && range->size == r->size);
+
+		/* check overlap with other range */
+		map_addr = ASI_RANGE_MAP_ADDR(r);
+		map_end = ASI_RANGE_MAP_END(r);
+		if (end < map_addr || addr >= map_end) {
+			/* no overlap, continue */
+			continue;
+		}
+
+		pr_debug("ASI %p: UNMAP %px/%lx/%d overlaps with %px/%lx/%d\n",
+			 asi, range->ptr, range->size, range->level,
+			 r->ptr, r->size, r->level);
+		r->overlap--;
+		overlap--;
+
+		/*
+		 * Check if range is included into a remaining mapped range.
+		 * If so then there's no need to unmap.
+		 */
+		if (map_addr <= addr && end <= map_end) {
+			pr_debug("ASI %p: UNMAP %px/%lx/%d still mapped\n",
+				 asi, range->ptr, range->size, range->level);
+			need_unmapping = false;
+		}
+	}
+
+	WARN_ON(overlap);
+
+	if (need_unmapping) {
+		asi_clear_pgd_range(asi, asi->pgd, addr, end, range->level);
+
+		/*
+		 * Remap all range we overlap with as mapping clearing
+		 * will have unmap the overlap.
+		 */
+		overlap = range->overlap;
+		list_for_each_entry(r, &asi->mapping_list, list) {
+			if (!overlap) {
+				/* no more overlap */
+				break;
+			}
+
+			/* check overlap with other range */
+			map_addr = ASI_RANGE_MAP_ADDR(r);
+			map_end = ASI_RANGE_MAP_END(r);
+			if (end < map_addr || addr >= map_end) {
+				/* no overlap, continue */
+				continue;
+			}
+			pr_debug("ASI %p: UNMAP %px/%lx/%d remaps %px/%lx/%d\n",
+				 asi, range->ptr, range->size, range->level,
+				 r->ptr, r->size, r->level);
+			overlap--;
+
+			r_addr = (unsigned long)r->ptr;
+			err = asi_copy_pgd_range(asi, asi->pgd,
+						 current->mm->pgd,
+						 r_addr, r_addr + r->size,
+						 r->level);
+			if (err) {
+				pr_debug("ASI %p: UNMAP %px/%lx/%d remaps %px/%lx/%d error %d\n",
+					 asi, range->ptr, range->size,
+					 range->level,
+					 r->ptr, r->size, r->level,
+					 err);
+			}
+		}
+	}
+}
+
 /*
  * Clear page table entries in the specified ASI page-table.
  */
@@ -797,8 +991,8 @@ void asi_unmap(struct asi *asi, void *ptr)
 	end = addr + range_mapping->size;
 	pr_debug("ASI %p: UNMAP %px/%lx/%d\n", asi, ptr,
 		 range_mapping->size, range_mapping->level);
-	asi_clear_pgd_range(asi, asi->pgd, addr, end, range_mapping->level);
 	list_del(&range_mapping->list);
+	asi_unmap_overlap(asi, range_mapping);
 	kfree(range_mapping);
 done:
 	spin_unlock_irqrestore(&asi->lock, flags);
-- 
1.7.1