mm: Make ksize() a reporting-only function

With all "silently resizing" callers of ksize() refactored, remove the
logic in ksize() that would allow it to be used to effectively change
the size of an allocation (bypassing __alloc_size hints, etc). Users
wanting this feature need to either use kmalloc_size_roundup() before an
allocation, or use krealloc() directly.

For kfree_sensitive(), move the unpoisoning logic inline. Replace the
some of the partially open-coded ksize() in __do_krealloc with ksize()
now that it doesn't perform unpoisoning.

Adjust the KUnit tests to match the new ksize() behavior. Execution
tested with:

$ ./tools/testing/kunit/kunit.py run \
	--kconfig_add CONFIG_KASAN=y \
	--kconfig_add CONFIG_KASAN_GENERIC=y \
	--arch x86_64 kasan

Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: linux-mm@kvack.org
Cc: kasan-dev@googlegroups.com
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Rientjes <rientjes@google.com>
Enhanced-by: Andrey Konovalov <andreyknvl@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

1 files changed, 10 insertions, 16 deletions

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 33b1886b06eb..7e96abf1bd7d 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1333,11 +1333,11 @@ __do_krealloc(const void *p, size_t new_size, gfp_t flags)
 	void *ret;
 	size_t ks;
 
-	/* Don't use instrumented ksize to allow precise KASAN poisoning. */
+	/* Check for double-free before calling ksize. */
 	if (likely(!ZERO_OR_NULL_PTR(p))) {
 		if (!kasan_check_byte(p))
 			return NULL;
-		ks = kfence_ksize(p) ?: __ksize(p);
+		ks = ksize(p);
 	} else
 		ks = 0;
 
@@ -1405,8 +1405,10 @@ void kfree_sensitive(const void *p)
 	void *mem = (void *)p;
 
 	ks = ksize(mem);
-	if (ks)
+	if (ks) {
+		kasan_unpoison_range(mem, ks);
 		memzero_explicit(mem, ks);
+	}
 	kfree(mem);
 }
 EXPORT_SYMBOL(kfree_sensitive);
@@ -1427,13 +1429,11 @@ EXPORT_SYMBOL(kfree_sensitive);
  */
 size_t ksize(const void *objp)
 {
-	size_t size;
-
 	/*
-	 * We need to first check that the pointer to the object is valid, and
-	 * only then unpoison the memory. The report printed from ksize() is
-	 * more useful, then when it's printed later when the behaviour could
-	 * be undefined due to a potential use-after-free or double-free.
+	 * We need to first check that the pointer to the object is valid.
+	 * The KASAN report printed from ksize() is more useful, then when
+	 * it's printed later when the behaviour could be undefined due to
+	 * a potential use-after-free or double-free.
 	 *
 	 * We use kasan_check_byte(), which is supported for the hardware
 	 * tag-based KASAN mode, unlike kasan_check_read/write().
@@ -1447,13 +1447,7 @@ size_t ksize(const void *objp)
 	if (unlikely(ZERO_OR_NULL_PTR(objp)) || !kasan_check_byte(objp))
 		return 0;
 
-	size = kfence_ksize(objp) ?: __ksize(objp);
-	/*
-	 * We assume that ksize callers could use whole allocated area,
-	 * so we need to unpoison this area.
-	 */
-	kasan_unpoison_range(objp, size);
-	return size;
+	return kfence_ksize(objp) ?: __ksize(objp);
 }
 EXPORT_SYMBOL(ksize);