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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id w9-20020a628209000000b0056276519e8fsm10507248pfd.73.2022.10.22.11.08.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 22 Oct 2022 11:08:36 -0700 (PDT) From: Kees Cook To: Christoph Lameter , Dmitry Vyukov Cc: Kees Cook , Jakub Kicinski , Paolo Abeni , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Vincenzo Frascino , linux-mm@kvack.org, kasan-dev@googlegroups.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH] mm: Make ksize() a reporting-only function Date: Sat, 22 Oct 2022 11:08:15 -0700 Message-Id: <20221022180455.never.023-kees@kernel.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=5852; h=from:subject:message-id; bh=HZuoaDzt6/LPxyvOVuzqy3FtD9MM88oVQvBYI2b7PvI=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBjVDGPT373RHlxlNzRB3FSVMPSd+3N5IOFs8nbEih6 a4JcCZSJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCY1QxjwAKCRCJcvTf3G3AJg0sEA CJQgeNhzT7kGutiZ6DfvUQ98sYDiSG8cy5fz0XvctLjXFa0E+0jHWMYAU49DaTSiJAPjvkJtC3eGqU 6H9Yhzx9OnK6+3Pf6CkgpLB2j2roioL0N9/uKNk3O/B2Zg1vC5X5WSChvXQKKYa/DWRZFjm1hYuSe6 eJtnb4TJbTlAswbsKtrfUiRdurXNZNeo93YLboPpjS3Oui2Zmkjs3yXUfQ0wbI1EAg7/Lt76SiyOEk xNIhZchALtO+3yxGXJbt5/E4CJQNgHyzMQ3zidIrYmZSMr0kRDJiFI7yTRmMMI0lBclAXkUM9DX4qW hRRkLsDseezDlETYXdhqTUlsufdXvAkrRPatPCnP/z66b+G0HAlR4Op/K5RMvloMen54XAbuXSCb3f szujhc7zJ0Ivi0uis3misDev9gs4NVzX6jAIfK9HQaWVf5ybskYfX13uIDyQUgrDAJ2zz9nkWvzhs2 4hTLhJWpQfeMm38oPVkvCP7IbG6I4mdB1J5OdiYiA8VeriacD3+wR/UupDY/Jj8Jg7UfZ1mOVC8sv5 om+rocuJfmZOlkrezs1scXeeSujkP68ukOUtcdRMlNVkHBcNBzjUQ0SGgx0J2ToE0V2CFsQEG4XXjz 833VvH5PsOTeK7/T5CefUcbv4z3/iq4+gl9YtUf8Rd5EvVizs2QIsOzNYy2g== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org 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. Cc: Dmitry Vyukov Cc: Jakub Kicinski Cc: Paolo Abeni Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Andrew Morton Cc: Vlastimil Babka Cc: Roman Gushchin Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: Andrey Ryabinin Cc: Alexander Potapenko Cc: Andrey Konovalov Cc: Vincenzo Frascino Cc: linux-mm@kvack.org Cc: kasan-dev@googlegroups.com Cc: netdev@vger.kernel.org Signed-off-by: Kees Cook Acked-by: Vlastimil Babka --- This requires at least this be landed first: https://lore.kernel.org/lkml/20221021234713.you.031-kees@kernel.org/ I suspect given that is the most central ksize() user, this ksize() fix might be best to land through the netdev tree... --- mm/kasan/kasan_test.c | 8 +++++--- mm/slab_common.c | 33 ++++++++++++++------------------- 2 files changed, 19 insertions(+), 22 deletions(-) diff --git a/mm/kasan/kasan_test.c b/mm/kasan/kasan_test.c index 0d59098f0876..cb5c54adb503 100644 --- a/mm/kasan/kasan_test.c +++ b/mm/kasan/kasan_test.c @@ -783,7 +783,7 @@ 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; @@ -791,15 +791,17 @@ 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'; + ptr[size - 1] = 'x'; /* This one must. */ - KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[real_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 33b1886b06eb..eabd66fcabd0 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); @@ -1415,10 +1417,11 @@ EXPORT_SYMBOL(kfree_sensitive); * ksize - get the actual amount of memory allocated for a given object * @objp: Pointer to the object * - * kmalloc may internally round up allocations and return more memory + * kmalloc() may internally round up allocations and return more memory * than requested. ksize() can be used to determine the actual amount of - * memory allocated. The caller may use this additional memory, even though - * a smaller amount of memory was initially specified with the kmalloc call. + * allocated memory. The caller may NOT use this additional memory, unless + * it calls krealloc(). To avoid an alloc/realloc cycle, callers can use + * kmalloc_size_roundup() to find the size of the associated kmalloc bucket. * The caller must guarantee that objp points to a valid object previously * allocated with either kmalloc() or kmem_cache_alloc(). The object * must not be freed during the duration of the call. @@ -1427,13 +1430,11 @@ 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 +1448,7 @@ 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);