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R. Silva" , Andrew Morton , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , llvm@lists.linux.dev, linux-hardening@vger.kernel.org, Mark Rutland , Miguel Ojeda , Marco Elver , linux-kernel@vger.kernel.org Subject: [PATCH 2/5] overflow: Expand check_add_overflow() for pointer addition Date: Mon, 29 Jan 2024 10:34:06 -0800 Message-Id: <20240129183411.3791340-2-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240129182845.work.694-kees@kernel.org> References: <20240129182845.work.694-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=10664; i=keescook@chromium.org; h=from:subject; bh=wU5wiWooVyd2eqSdpoTBHd90qKwM9wZ/F9mLDiaQmqs=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlt++hOmJWNChP5gjc4TpxLGURO5jKzEEgWMbHO GpeBzggvUWJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZbfvoQAKCRCJcvTf3G3A JshUD/4mfIxZHN04yZHdDDv+6B1mABxoQcm8MH8k5+dd+1Cg2mWb2V4dyLaHGOAXy0VSNJfF/EP O+vimDvJMsIZdST6MlKaXVJlZf+eFfG6AafkEtRLoBtBpXCj+FXSXt+dDhCCaW/iLHhdEDk3KYa DmmGSN8Adg1hdRFmVDiUXRefTS62WOY/jaZVomk9moOg8doMlKC3812t7dtp3qoeaWIRBIr/bMM wV43sD2nLqxSItSJD61I5sBZVOENslq1ibBg8BEQNkGV2VlR1mW57dYhFqIki2dZzU8cyPTi5bo 1lkHC9FI/xA6xEZ/xk/X2FM1Z7/QY1Cnt3C3HcjsEuq9v/XkP4bJRzyybEHSHRUfDS7AYD3QodD pH53rdjtqpYXmCXu77+XnR3e1r06vIWqhEHC+OCfhUruHhRUnh80seJbjLf9JT0vBBy/pYKNj2d Si0NuZy4FAN5ZtqOOSMV0FBWt3trfnSrfdg08H8FnJZ4ArlNcxD4+8DteNXDLYShnJCUN0tIfKr PBnqZGcPOGapoFOOA2GY+lSZPS3tKYH6hsfAfm4Y9e1XxIT3AG/9bv6GBhLRDm4Fh84ksGdEXVK 1wOrPvVNg2y8tgCPDXr41Tzuces9sa6QPztqCxgKFVZ1OL+o98SdArPyOeP+aQt2aRXa/wk0KQI jSPhzQFtz2fupRQ== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 The check_add_overflow() helper is mostly a wrapper around __builtin_add_overflow(), but GCC and Clang refuse to operate on pointer arguments that would normally be allowed if the addition were open-coded. For example, we have many places where pointer overflow is tested: struct foo *ptr; ... /* Check for overflow */ if (ptr + count < ptr) ... And in order to avoid running into the overflow sanitizers in the future, we need to rewrite these "intended" overflow checks: if (check_add_overflow(ptr, count, &result)) ... Frustratingly the argument type validation for __builtin_add_overflow() is done before evaluating __builtin_choose_expr(), so for arguments to be valid simultaneously for sizeof(*p) (when p may not be a pointer), and __builtin_add_overflow(a, ...) (when a may be a pointer), we must introduce wrappers that always produce a specific type (but they are only used in the places where the bogus arguments will be ignored). To test whether a variable is a pointer or not, introduce the __is_ptr() helper, which uses __builtin_classify_type() to find arrays and pointers (via the new __is_ptr_or_array() helper), and then decays arrays into pointers (via the new __decay() helper), to distinguish pointers from arrays. Additionally update the unit tests to cover pointer addition. Cc: Rasmus Villemoes Cc: "Gustavo A. R. Silva" Cc: Andrew Morton Cc: Nathan Chancellor Cc: Nick Desaulniers Cc: Bill Wendling Cc: Justin Stitt Cc: llvm@lists.linux.dev Cc: linux-hardening@vger.kernel.org Signed-off-by: Kees Cook --- include/linux/compiler_types.h | 10 +++++ include/linux/overflow.h | 44 ++++++++++++++++++- lib/overflow_kunit.c | 77 ++++++++++++++++++++++++++++++---- 3 files changed, 120 insertions(+), 11 deletions(-) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 6f1ca49306d2..d27b58fddfaa 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -375,6 +375,16 @@ struct ftrace_likely_data { /* Are two types/vars the same type (ignoring qualifiers)? */ #define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b)) +/* Is variable addressable? */ +#define __is_ptr_or_array(p) (__builtin_classify_type(p) == 5) + +/* Return an array decayed to a pointer. */ +#define __decay(p) \ + (&*__builtin_choose_expr(__is_ptr_or_array(p), p, NULL)) + +/* Report if variable is a pointer type. */ +#define __is_ptr(p) __same_type(p, __decay(p)) + /* * __unqual_scalar_typeof(x) - Declare an unqualified scalar type, leaving * non-scalar types unchanged. diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 4e741ebb8005..210e5602e89b 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -51,6 +51,43 @@ static inline bool __must_check __must_check_overflow(bool overflow) return unlikely(overflow); } +/* Always produce an integral variable expression. */ +#define __filter_integral(x) \ + __builtin_choose_expr(!__is_ptr(x), (x), 0) + +/* Always produce a pointer value. */ +#define __filter_ptr(x) \ + __builtin_choose_expr(__is_ptr(x), (x), NULL) + +/* Always produce a pointer to an integral value. */ +#define __filter_ptrint(x) \ + __builtin_choose_expr(!__is_ptr(*(x)), x, &(int){ 0 }) + +/** + * __check_ptr_add_overflow() - Calculate pointer addition with overflow checking + * @a: pointer addend + * @b: numeric addend + * @d: pointer to store sum + * + * Returns 0 on success, 1 on wrap-around. + * + * Do not use this function directly, use check_add_overflow() instead. + * + * *@d holds the results of the attempted addition, which may wrap-around. + */ +#define __check_ptr_add_overflow(a, b, d) \ + ({ \ + typeof(a) __a = (a); \ + typeof(b) __b = (b); \ + size_t __bytes; \ + bool __overflow; \ + \ + /* we want to perform the wrap-around, but retain the result */ \ + __overflow = __builtin_mul_overflow(sizeof(*(__a)), __b, &__bytes); \ + __builtin_add_overflow((unsigned long)(__a), __bytes, (unsigned long *)(d)) || \ + __overflow; \ + }) + /** * check_add_overflow() - Calculate addition with overflow checking * @a: first addend @@ -61,8 +98,11 @@ static inline bool __must_check __must_check_overflow(bool overflow) * * *@d holds the results of the attempted addition, which may wrap-around. */ -#define check_add_overflow(a, b, d) \ - __must_check_overflow(__builtin_add_overflow(a, b, d)) +#define check_add_overflow(a, b, d) \ + __must_check_overflow(__builtin_choose_expr(__is_ptr(a), \ + __check_ptr_add_overflow(__filter_ptr(a), b, d), \ + __builtin_add_overflow(__filter_integral(a), b, \ + __filter_ptrint(d)))) /** * check_sub_overflow() - Calculate subtraction with overflow checking diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c index c527f6b75789..2d106e880956 100644 --- a/lib/overflow_kunit.c +++ b/lib/overflow_kunit.c @@ -45,13 +45,18 @@ # define SKIP_64_ON_32(t) do { } while (0) #endif -#define DEFINE_TEST_ARRAY_TYPED(t1, t2, t) \ - static const struct test_ ## t1 ## _ ## t2 ## __ ## t { \ +#define DEFINE_TEST_ARRAY_NAMED_TYPED(n1, n2, n, t1, t2, t) \ + static const struct test_ ## n1 ## _ ## n2 ## __ ## n { \ t1 a; \ t2 b; \ - t sum, diff, prod; \ + t sum; \ + t diff; \ + t prod; \ bool s_of, d_of, p_of; \ - } t1 ## _ ## t2 ## __ ## t ## _tests[] + } n1 ## _ ## n2 ## __ ## n ## _tests[] + +#define DEFINE_TEST_ARRAY_TYPED(t1, t2, t) \ + DEFINE_TEST_ARRAY_NAMED_TYPED(t1, t2, t, t1, t2, t) #define DEFINE_TEST_ARRAY(t) DEFINE_TEST_ARRAY_TYPED(t, t, t) @@ -251,8 +256,10 @@ DEFINE_TEST_ARRAY(s64) = { }; #define check_one_op(t, fmt, op, sym, a, b, r, of) do { \ - int _a_orig = a, _a_bump = a + 1; \ - int _b_orig = b, _b_bump = b + 1; \ + typeof(a + 0) _a_orig = a; \ + typeof(a + 0) _a_bump = a + 1; \ + typeof(b + 0) _b_orig = b; \ + typeof(b + 0) _b_bump = b + 1; \ bool _of; \ t _r; \ \ @@ -260,13 +267,13 @@ DEFINE_TEST_ARRAY(s64) = { KUNIT_EXPECT_EQ_MSG(test, _of, of, \ "expected "fmt" "sym" "fmt" to%s overflow (type %s)\n", \ a, b, of ? "" : " not", #t); \ - KUNIT_EXPECT_EQ_MSG(test, _r, r, \ + KUNIT_EXPECT_TRUE_MSG(test, _r == r, \ "expected "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \ a, b, r, _r, #t); \ /* Check for internal macro side-effects. */ \ _of = check_ ## op ## _overflow(_a_orig++, _b_orig++, &_r); \ - KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, "Unexpected " #op " macro side-effect!\n"); \ - KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, "Unexpected " #op " macro side-effect!\n"); \ + KUNIT_EXPECT_TRUE_MSG(test, _a_orig == _a_bump, "Unexpected " #op " macro side-effect!\n"); \ + KUNIT_EXPECT_TRUE_MSG(test, _b_orig == _b_bump, "Unexpected " #op " macro side-effect!\n"); \ } while (0) #define DEFINE_TEST_FUNC_TYPED(n, t, fmt) \ @@ -333,6 +340,55 @@ DEFINE_TEST_ARRAY_TYPED(int, int, u8) = { }; DEFINE_TEST_FUNC_TYPED(int_int__u8, u8, "%d"); +#define DEFINE_TEST_PTR_FUNC_TYPED(n, t, fmt) \ +static void do_ptr_test_ ## n(struct kunit *test, const struct test_ ## n *p) \ +{ \ + /* we're only doing single-direction sums, no product or division */ \ + check_one_op(t, fmt, add, "+", p->a, p->b, p->sum, p->s_of);\ +} \ + \ +static void n ## _overflow_test(struct kunit *test) { \ + unsigned i; \ + \ + for (i = 0; i < ARRAY_SIZE(n ## _tests); ++i) \ + do_ptr_test_ ## n(test, &n ## _tests[i]); \ + kunit_info(test, "%zu %s arithmetic tests finished\n", \ + ARRAY_SIZE(n ## _tests), #n); \ +} + +DEFINE_TEST_ARRAY_NAMED_TYPED(void, int, void, void *, int, void *) = { + {NULL, 0, NULL, NULL, NULL, false, false, false}, + {(void *)0x30, 0x10, (void *)0x40, NULL, NULL, false, false, false}, + {(void *)ULONG_MAX, 0, (void *)ULONG_MAX, NULL, NULL, false, false, false}, + {(void *)ULONG_MAX, 1, NULL, NULL, NULL, true, false, false}, + {(void *)ULONG_MAX, INT_MAX, (void *)(INT_MAX - 1), NULL, NULL, true, false, false}, +}; +DEFINE_TEST_PTR_FUNC_TYPED(void_int__void, void *, "%lx"); + +struct _sized { + int a; + char b; +}; + +DEFINE_TEST_ARRAY_NAMED_TYPED(sized, int, sized, struct _sized *, int, struct _sized *) = { + {NULL, 0, NULL, NULL, NULL, false, false, false}, + {NULL, 1, (struct _sized *)(sizeof(struct _sized)), NULL, NULL, false, false, false}, + {NULL, 0x10, (struct _sized *)(sizeof(struct _sized) * 0x10), NULL, NULL, false, false, false}, + {(void *)(ULONG_MAX - sizeof(struct _sized)), 1, (struct _sized *)ULONG_MAX, NULL, NULL, false, false, false}, + {(void *)(ULONG_MAX - sizeof(struct _sized) + 1), 1, NULL, NULL, NULL, true, false, false}, + {(void *)(ULONG_MAX - sizeof(struct _sized) + 1), 2, (struct _sized *)(sizeof(struct _sized)), NULL, NULL, true, false, false}, + {(void *)(ULONG_MAX - sizeof(struct _sized) + 1), 3, (struct _sized *)(sizeof(struct _sized) * 2), NULL, NULL, true, false, false}, +}; +DEFINE_TEST_PTR_FUNC_TYPED(sized_int__sized, struct _sized *, "%lx"); + +DEFINE_TEST_ARRAY_NAMED_TYPED(sized, size_t, sized, struct _sized *, size_t, struct _sized *) = { + {NULL, 0, NULL, NULL, NULL, false, false, false}, + {NULL, 1, (struct _sized *)(sizeof(struct _sized)), NULL, NULL, false, false, false}, + {NULL, 0x10, (struct _sized *)(sizeof(struct _sized) * 0x10), NULL, NULL, false, false, false}, + {NULL, SIZE_MAX - 10, (struct _sized *)18446744073709551528UL, NULL, NULL, true, false, false}, +}; +DEFINE_TEST_PTR_FUNC_TYPED(sized_size_t__sized, struct _sized *, "%zu"); + /* Args are: value, shift, type, expected result, overflow expected */ #define TEST_ONE_SHIFT(a, s, t, expect, of) do { \ typeof(a) __a = (a); \ @@ -1122,6 +1178,9 @@ static struct kunit_case overflow_test_cases[] = { KUNIT_CASE(s32_s32__s32_overflow_test), KUNIT_CASE(u64_u64__u64_overflow_test), KUNIT_CASE(s64_s64__s64_overflow_test), + KUNIT_CASE(void_int__void_overflow_test), + KUNIT_CASE(sized_int__sized_overflow_test), + KUNIT_CASE(sized_size_t__sized_overflow_test), KUNIT_CASE(u32_u32__int_overflow_test), KUNIT_CASE(u32_u32__u8_overflow_test), KUNIT_CASE(u8_u8__int_overflow_test),