+ kasan-mm-optimize-krealloc-poisoning.patch added to -mm tree

* + kasan-mm-optimize-krealloc-poisoning.patch added to -mm tree
@ 2021-02-05 21:18 akpm
  0 siblings, 0 replies; 2+ messages in thread
From: akpm @ 2021-02-05 21:18 UTC (permalink / raw)
  To: andreyknvl, aryabinin, Branislav.Rankov, catalin.marinas,
	dvyukov, elver, eugenis, glider, kevin.brodsky, mm-commits, pcc,
	vincenzo.frascino, will.deacon


The patch titled
     Subject: kasan, mm: optimize krealloc poisoning
has been added to the -mm tree.  Its filename is
     kasan-mm-optimize-krealloc-poisoning.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/kasan-mm-optimize-krealloc-poisoning.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/kasan-mm-optimize-krealloc-poisoning.patch

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------------------------------------------------------
From: Andrey Konovalov <andreyknvl@google.com>
Subject: kasan, mm: optimize krealloc poisoning

Currently, krealloc() always calls ksize(), which unpoisons the whole
object including the redzone.  This is inefficient, as kasan_krealloc()
repoisons the redzone for objects that fit into the same buffer.

This patch changes krealloc() instrumentation to use uninstrumented
__ksize() that doesn't unpoison the memory.  Instead, kasan_kreallos() is
changed to unpoison the memory excluding the redzone.

For objects that don't fit into the old allocation, this patch disables
KASAN accessibility checks when copying memory into a new object instead
of unpoisoning it.

Link: https://lkml.kernel.org/r/9bef90327c9cb109d736c40115684fd32f49e6b0.1612546384.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/kasan/common.c |   12 ++++++++++--
 mm/slab_common.c  |   20 ++++++++++++++------
 2 files changed, 24 insertions(+), 8 deletions(-)

--- a/mm/kasan/common.c~kasan-mm-optimize-krealloc-poisoning
+++ a/mm/kasan/common.c
@@ -476,7 +476,7 @@ static void *____kasan_kmalloc(struct km
 
 	/*
 	 * The object has already been unpoisoned by kasan_slab_alloc() for
-	 * kmalloc() or by ksize() for krealloc().
+	 * kmalloc() or by kasan_krealloc() for krealloc().
 	 */
 
 	/*
@@ -526,7 +526,7 @@ void * __must_check __kasan_kmalloc_larg
 
 	/*
 	 * The object has already been unpoisoned by kasan_alloc_pages() for
-	 * alloc_pages() or by ksize() for krealloc().
+	 * alloc_pages() or by kasan_krealloc() for krealloc().
 	 */
 
 	/*
@@ -554,8 +554,16 @@ void * __must_check __kasan_krealloc(con
 	if (unlikely(object == ZERO_SIZE_PTR))
 		return (void *)object;
 
+	/*
+	 * Unpoison the object's data.
+	 * Part of it might already have been unpoisoned, but it's unknown
+	 * how big that part is.
+	 */
+	kasan_unpoison(object, size);
+
 	page = virt_to_head_page(object);
 
+	/* Piggy-back on kmalloc() instrumentation to poison the redzone. */
 	if (unlikely(!PageSlab(page)))
 		return __kasan_kmalloc_large(object, size, flags);
 	else
--- a/mm/slab_common.c~kasan-mm-optimize-krealloc-poisoning
+++ a/mm/slab_common.c
@@ -1061,19 +1061,27 @@ static __always_inline void *__do_kreall
 	void *ret;
 	size_t ks;
 
-	if (likely(!ZERO_OR_NULL_PTR(p)) && !kasan_check_byte(p))
-		return NULL;
-
-	ks = ksize(p);
+	/* Don't use instrumented ksize to allow precise KASAN poisoning. */
+	if (likely(!ZERO_OR_NULL_PTR(p))) {
+		if (!kasan_check_byte(p))
+			return NULL;
+		ks = kfence_ksize(p) ?: __ksize(p);
+	} else
+		ks = 0;
 
+	/* If the object still fits, repoison it precisely. */
 	if (ks >= new_size) {
 		p = kasan_krealloc((void *)p, new_size, flags);
 		return (void *)p;
 	}
 
 	ret = kmalloc_track_caller(new_size, flags);
-	if (ret && p)
-		memcpy(ret, p, ks);
+	if (ret && p) {
+		/* Disable KASAN checks as the object's redzone is accessed. */
+		kasan_disable_current();
+		memcpy(ret, kasan_reset_tag(p), ks);
+		kasan_enable_current();
+	}
 
 	return ret;
 }
_

Patches currently in -mm which might be from andreyknvl@google.com are

kasan-prefix-global-functions-with-kasan_.patch
kasan-clarify-hw_tags-impact-on-tbi.patch
kasan-clean-up-comments-in-tests.patch
kasan-add-macros-to-simplify-checking-test-constraints.patch
kasan-add-match-all-tag-tests.patch
kasan-arm64-allow-using-kunit-tests-with-hw_tags-mode.patch
kasan-rename-config_test_kasan_module.patch
kasan-add-compiler-barriers-to-kunit_expect_kasan_fail.patch
kasan-adapt-kmalloc_uaf2-test-to-hw_tags-mode.patch
kasan-fix-memory-corruption-in-kasan_bitops_tags-test.patch
kasan-move-_ret_ip_-to-inline-wrappers.patch
kasan-fix-bug-detection-via-ksize-for-hw_tags-mode.patch
kasan-add-proper-page-allocator-tests.patch
kasan-add-a-test-for-kmem_cache_alloc-free_bulk.patch
kasan-dont-run-tests-when-kasan-is-not-enabled.patch
kfence-kasan-make-kfence-compatible-with-kasan-fix-2.patch
kasan-mm-dont-save-alloc-stacks-twice.patch
kasan-mm-optimize-kmalloc-poisoning.patch
kasan-optimize-large-kmalloc-poisoning.patch
kasan-clean-up-setting-free-info-in-kasan_slab_free.patch
kasan-unify-large-kfree-checks.patch
kasan-rework-krealloc-tests.patch
kasan-mm-fail-krealloc-on-freed-objects.patch
kasan-mm-optimize-krealloc-poisoning.patch
kasan-ensure-poisoning-size-alignment.patch
arm64-kasan-simplify-and-inline-mte-functions.patch
kasan-inline-hw_tags-helper-functions.patch
arm64-kasan-export-mte-symbols-for-kasan-tests.patch
kasan-clarify-that-only-first-bug-is-reported-in-hw_tags.patch


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