On 11/18/22 04:56, Kees Cook wrote: > With all "silently resizing" callers of ksize() refactored, remove the At cursory look seems it's true now in -next (but not mainline?) can you confirm? That would probably be safe enough to have slab.git expose this to -next now and time a PR appropriately in the next merge window? > 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. > > Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx> > Cc: Christoph Lameter <cl@xxxxxxxxx> > Cc: Pekka Enberg <penberg@xxxxxxxxxx> > Cc: David Rientjes <rientjes@xxxxxxxxxx> > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx> > Cc: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> > Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> > Cc: Alexander Potapenko <glider@xxxxxxxxxx> > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> > Cc: linux-mm@xxxxxxxxx > Cc: kasan-dev@xxxxxxxxxxxxxxxx > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > --- > v2: > - improve kunit test precision (andreyknvl) > - add Ack (vbabka) > v1: https://lore.kernel.org/all/20221022180455.never.023-kees@xxxxxxxxxx > --- > mm/kasan/kasan_test.c | 14 +++++++++----- > mm/slab_common.c | 26 ++++++++++---------------- > 2 files changed, 19 insertions(+), 21 deletions(-) > > diff --git a/mm/kasan/kasan_test.c b/mm/kasan/kasan_test.c > index 7502f03c807c..fc4b22916587 100644 > --- a/mm/kasan/kasan_test.c > +++ b/mm/kasan/kasan_test.c > @@ -821,7 +821,7 @@ 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; > @@ -829,15 +829,19 @@ static void ksize_unpoisons_memory(struct kunit *test) > > 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. */ > + KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[size]); > + KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[real_size - 1]); > > kfree(ptr); > } > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 8276022f0da4..27caa57af070 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -1335,11 +1335,11 @@ __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; > > @@ -1407,21 +1407,21 @@ 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); > > 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(). > @@ -1435,13 +1435,7 @@ 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); >
