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mm: Make ksize() a reporting-only function

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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>
This commit is contained in:
Kees Cook 2022-09-22 13:08:16 -07:00
parent 9124a26401
commit 38931d8989
2 changed files with 23 additions and 22 deletions
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19
mm/kasan/kasan_test.c
View File

@ -783,23 +783,30 @@ static void kasan_global_oob_left(struct kunit *test)
KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p);
}
/* Check that ksize() makes the whole object accessible. */
/* Check that ksize() does NOT unpoison whole object. */
static void ksize_unpoisons_memory(struct kunit *test)
{
char *ptr;
size_t size = 123, real_size;
size_t size = 128 - KASAN_GRANULE_SIZE - 5;
size_t real_size;
ptr = kmalloc(size, GFP_KERNEL);
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
real_size = ksize(ptr);
KUNIT_EXPECT_GT(test, real_size, size);
OPTIMIZER_HIDE_VAR(ptr);
/* This access shouldn't trigger a KASAN report. */
ptr[size] = 'x';
/* These accesses shouldn't trigger a KASAN report. */
ptr[0] = 'x';
ptr[size - 1] = 'x';
/* This one must. */
KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[real_size]);
/* These must trigger a KASAN report. */
if (IS_ENABLED(CONFIG_KASAN_GENERIC))
KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[size]);
KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[size + 5]);
KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[real_size - 1]);
kfree(ptr);
}

26
mm/slab_common.c
View File

@ -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);