x86/intel_rdt: Fix out-of-bounds memory access in CBM tests

While the DOC at the beginning of lib/bitmap.c explicitly states that
"The number of valid bits in a given bitmap does _not_ need to be an
exact multiple of BITS_PER_LONG.", some of the bitmap operations do
indeed access BITS_PER_LONG portions of the provided bitmap no matter
the size of the provided bitmap. For example, if bitmap_intersects()
is provided with an 8 bit bitmap the operation will access
BITS_PER_LONG bits from the provided bitmap. While the operation
ensures that these extra bits do not affect the result, the memory
is still accessed.

The capacity bitmasks (CBMs) are typically stored in u32 since they
can never exceed 32 bits. A few instances exist where a bitmap_*
operation is performed on a CBM by simply pointing the bitmap operation
to the stored u32 value.

The consequence of this pattern is that some bitmap_* operations will
access out-of-bounds memory when interacting with the provided CBM. This
is confirmed with a KASAN test that reports:

 BUG: KASAN: stack-out-of-bounds in __bitmap_intersects+0xa2/0x100

and

 BUG: KASAN: stack-out-of-bounds in __bitmap_weight+0x58/0x90

Fix this by moving any CBM provided to a bitmap operation needing
BITS_PER_LONG to an 'unsigned long' variable.

[ tglx: Changed related function arguments to unsigned long and got rid
	of the _cbm extra step ]

Fixes: 72d50505 ("x86/intel_rdt: Add utilities to test pseudo-locked region possibility")
Fixes: 49f7b4ef ("x86/intel_rdt: Enable setting of exclusive mode")
Fixes: d9b48c86 ("x86/intel_rdt: Display resource groups' allocations' size in bytes")
Fixes: 95f0b77e ("x86/intel_rdt: Initialize new resource group with sane defaults")
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Cc: gavin.hindman@intel.com
Cc: jithu.joseph@intel.com
Cc: dave.hansen@intel.com
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/69a428613a53f10e80594679ac726246020ff94f.1538686926.git.reinette.chatre@intel.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/cpu/intel_rdt.h

@@ -529,14 +529,14 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
 int rdtgroup_schemata_show(struct kernfs_open_file *of,
 			   struct seq_file *s, void *v);
 bool rdtgroup_cbm_overlaps(struct rdt_resource *r, struct rdt_domain *d,
-			   u32 _cbm, int closid, bool exclusive);
+			   unsigned long cbm, int closid, bool exclusive);
 unsigned int rdtgroup_cbm_to_size(struct rdt_resource *r, struct rdt_domain *d,
-				  u32 cbm);
+				  unsigned long cbm);
 enum rdtgrp_mode rdtgroup_mode_by_closid(int closid);
 int rdtgroup_tasks_assigned(struct rdtgroup *r);
 int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
 int rdtgroup_locksetup_exit(struct rdtgroup *rdtgrp);
-bool rdtgroup_cbm_overlaps_pseudo_locked(struct rdt_domain *d, u32 _cbm);
+bool rdtgroup_cbm_overlaps_pseudo_locked(struct rdt_domain *d, unsigned long cbm);
 bool rdtgroup_pseudo_locked_in_hierarchy(struct rdt_domain *d);
 int rdt_pseudo_lock_init(void);
 void rdt_pseudo_lock_release(void);

arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c

@@ -797,25 +797,27 @@ int rdtgroup_locksetup_exit(struct rdtgroup *rdtgrp)
 /**
  * rdtgroup_cbm_overlaps_pseudo_locked - Test if CBM or portion is pseudo-locked
  * @d: RDT domain
- * @_cbm: CBM to test
+ * @cbm: CBM to test
  *
- * @d represents a cache instance and @_cbm a capacity bitmask that is
- * considered for it. Determine if @_cbm overlaps with any existing
+ * @d represents a cache instance and @cbm a capacity bitmask that is
+ * considered for it. Determine if @cbm overlaps with any existing
  * pseudo-locked region on @d.
  *
- * Return: true if @_cbm overlaps with pseudo-locked region on @d, false
+ * @cbm is unsigned long, even if only 32 bits are used, to make the
+ * bitmap functions work correctly.
+ *
+ * Return: true if @cbm overlaps with pseudo-locked region on @d, false
  * otherwise.
  */
-bool rdtgroup_cbm_overlaps_pseudo_locked(struct rdt_domain *d, u32 _cbm)
+bool rdtgroup_cbm_overlaps_pseudo_locked(struct rdt_domain *d, unsigned long cbm)
 {
-	unsigned long *cbm = (unsigned long *)&_cbm;
-	unsigned long *cbm_b;
 	unsigned int cbm_len;
+	unsigned long cbm_b;
 
 	if (d->plr) {
 		cbm_len = d->plr->r->cache.cbm_len;
-		cbm_b = (unsigned long *)&d->plr->cbm;
-		if (bitmap_intersects(cbm, cbm_b, cbm_len))
+		cbm_b = d->plr->cbm;
+		if (bitmap_intersects(&cbm, &cbm_b, cbm_len))
 			return true;
 	}
 	return false;

arch/x86/kernel/cpu/intel_rdt_rdtgroup.c

@@ -975,33 +975,34 @@ static int rdtgroup_mode_show(struct kernfs_open_file *of,
  * is false then overlaps with any resource group or hardware entities
  * will be considered.
  *
+ * @cbm is unsigned long, even if only 32 bits are used, to make the
+ * bitmap functions work correctly.
+ *
  * Return: false if CBM does not overlap, true if it does.
  */
 bool rdtgroup_cbm_overlaps(struct rdt_resource *r, struct rdt_domain *d,
-			   u32 _cbm, int closid, bool exclusive)
+			   unsigned long cbm, int closid, bool exclusive)
 {
-	unsigned long *cbm = (unsigned long *)&_cbm;
-	unsigned long *ctrl_b;
 	enum rdtgrp_mode mode;
+	unsigned long ctrl_b;
 	u32 *ctrl;
 	int i;
 
 	/* Check for any overlap with regions used by hardware directly */
 	if (!exclusive) {
-		if (bitmap_intersects(cbm,
-				      (unsigned long *)&r->cache.shareable_bits,
-				      r->cache.cbm_len))
+		ctrl_b = r->cache.shareable_bits;
+		if (bitmap_intersects(&cbm, &ctrl_b, r->cache.cbm_len))
 			return true;
 	}
 
 	/* Check for overlap with other resource groups */
 	ctrl = d->ctrl_val;
 	for (i = 0; i < closids_supported(); i++, ctrl++) {
-		ctrl_b = (unsigned long *)ctrl;
+		ctrl_b = *ctrl;
 		mode = rdtgroup_mode_by_closid(i);
 		if (closid_allocated(i) && i != closid &&
 		    mode != RDT_MODE_PSEUDO_LOCKSETUP) {
-			if (bitmap_intersects(cbm, ctrl_b, r->cache.cbm_len)) {
+			if (bitmap_intersects(&cbm, &ctrl_b, r->cache.cbm_len)) {
 				if (exclusive) {
 					if (mode == RDT_MODE_EXCLUSIVE)
 						return true;
@@ -1138,15 +1139,18 @@ static ssize_t rdtgroup_mode_write(struct kernfs_open_file *of,
  * computed by first dividing the total cache size by the CBM length to
  * determine how many bytes each bit in the bitmask represents. The result
  * is multiplied with the number of bits set in the bitmask.
+ *
+ * @cbm is unsigned long, even if only 32 bits are used to make the
+ * bitmap functions work correctly.
  */
 unsigned int rdtgroup_cbm_to_size(struct rdt_resource *r,
-				  struct rdt_domain *d, u32 cbm)
+				  struct rdt_domain *d, unsigned long cbm)
 {
 	struct cpu_cacheinfo *ci;
 	unsigned int size = 0;
 	int num_b, i;
 
-	num_b = bitmap_weight((unsigned long *)&cbm, r->cache.cbm_len);
+	num_b = bitmap_weight(&cbm, r->cache.cbm_len);
 	ci = get_cpu_cacheinfo(cpumask_any(&d->cpu_mask));
 	for (i = 0; i < ci->num_leaves; i++) {
 		if (ci->info_list[i].level == r->cache_level) {
@@ -2353,6 +2357,7 @@ static int rdtgroup_init_alloc(struct rdtgroup *rdtgrp)
 	u32 used_b = 0, unused_b = 0;
 	u32 closid = rdtgrp->closid;
 	struct rdt_resource *r;
+	unsigned long tmp_cbm;
 	enum rdtgrp_mode mode;
 	struct rdt_domain *d;
 	int i, ret;
@@ -2390,9 +2395,14 @@ static int rdtgroup_init_alloc(struct rdtgroup *rdtgrp)
 			 * modify the CBM based on system availability.
 			 */
 			cbm_ensure_valid(&d->new_ctrl, r);
-			if (bitmap_weight((unsigned long *) &d->new_ctrl,
-					  r->cache.cbm_len) <
-					r->cache.min_cbm_bits) {
+			/*
+			 * Assign the u32 CBM to an unsigned long to ensure
+			 * that bitmap_weight() does not access out-of-bound
+			 * memory.
+			 */
+			tmp_cbm = d->new_ctrl;
+			if (bitmap_weight(&tmp_cbm, r->cache.cbm_len) <
+			    r->cache.min_cbm_bits) {
 				rdt_last_cmd_printf("no space on %s:%d\n",
 						    r->name, d->id);
 				return -ENOSPC;