From 0a6a5f8656ccf9a60ac516c68cd4eb40ff4630c4 Mon Sep 17 00:00:00 2001 From: David Malcolm Date: Tue, 20 Feb 2024 19:44:51 -0500 Subject: [PATCH] analyzer: handle array-initialization from a string_cst [PR113999] gcc/analyzer/ChangeLog: PR analyzer/113999 * analyzer.h (get_string_cst_size): New decl. * region-model-manager.cc (get_string_cst_size): New. (region_model_manager::maybe_get_char_from_string_cst): Treat single-byte accesses within string_cst but beyond TREE_STRING_LENGTH as being 0. * region-model.cc (string_cst_has_null_terminator): Likewise. gcc/testsuite/ChangeLog: PR analyzer/113999 * c-c++-common/analyzer/strlen-pr113999.c: New test. * gcc.dg/analyzer/strlen-1.c: More test coverage. Signed-off-by: David Malcolm --- gcc/analyzer/analyzer.h | 3 ++ gcc/analyzer/region-model-manager.cc | 35 +++++++++++-- gcc/analyzer/region-model.cc | 17 +++++- .../c-c++-common/analyzer/strlen-pr113999.c | 8 +++ gcc/testsuite/gcc.dg/analyzer/strlen-1.c | 52 +++++++++++++++++++ 5 files changed, 109 insertions(+), 6 deletions(-) create mode 100644 gcc/testsuite/c-c++-common/analyzer/strlen-pr113999.c diff --git a/gcc/analyzer/analyzer.h b/gcc/analyzer/analyzer.h index 23e3f71df0a..20a8e3f9a1d 100644 --- a/gcc/analyzer/analyzer.h +++ b/gcc/analyzer/analyzer.h @@ -430,6 +430,9 @@ byte_offset_to_json (const byte_offset_t &offset); extern tristate compare_constants (tree lhs_const, enum tree_code op, tree rhs_const); +extern tree +get_string_cst_size (const_tree string_cst); + } // namespace ana extern bool is_special_named_call_p (const gcall *call, const char *funcname, diff --git a/gcc/analyzer/region-model-manager.cc b/gcc/analyzer/region-model-manager.cc index 21e13b48025..93e72ec45a8 100644 --- a/gcc/analyzer/region-model-manager.cc +++ b/gcc/analyzer/region-model-manager.cc @@ -1407,6 +1407,20 @@ get_or_create_const_fn_result_svalue (tree type, return const_fn_result_sval; } +/* Get a tree for the size of STRING_CST, or NULL_TREE. + Note that this may be larger than TREE_STRING_LENGTH (implying + a run of trailing zero bytes from TREE_STRING_LENGTH up to this + higher limit). */ + +tree +get_string_cst_size (const_tree string_cst) +{ + gcc_assert (TREE_CODE (string_cst) == STRING_CST); + gcc_assert (TREE_CODE (TREE_TYPE (string_cst)) == ARRAY_TYPE); + + return TYPE_SIZE_UNIT (TREE_TYPE (string_cst)); +} + /* Given STRING_CST, a STRING_CST and BYTE_OFFSET_CST a constant, attempt to get the character at that offset, returning either the svalue for the character constant, or NULL if unsuccessful. */ @@ -1420,16 +1434,27 @@ region_model_manager::maybe_get_char_from_string_cst (tree string_cst, /* Adapted from fold_read_from_constant_string. */ scalar_int_mode char_mode; if (TREE_CODE (byte_offset_cst) == INTEGER_CST - && compare_tree_int (byte_offset_cst, - TREE_STRING_LENGTH (string_cst)) < 0 && is_int_mode (TYPE_MODE (TREE_TYPE (TREE_TYPE (string_cst))), &char_mode) && GET_MODE_SIZE (char_mode) == 1) { + /* If we're beyond the string_cst, the read is unsuccessful. */ + if (compare_constants (byte_offset_cst, + GE_EXPR, + get_string_cst_size (string_cst)).is_true ()) + return NULL; + + int char_val; + if (compare_tree_int (byte_offset_cst, + TREE_STRING_LENGTH (string_cst)) < 0) + /* We're within the area defined by TREE_STRING_POINTER. */ + char_val = (TREE_STRING_POINTER (string_cst) + [TREE_INT_CST_LOW (byte_offset_cst)]); + else + /* We're in the padding area of trailing zeroes. */ + char_val = 0; tree char_cst - = build_int_cst_type (TREE_TYPE (TREE_TYPE (string_cst)), - (TREE_STRING_POINTER (string_cst) - [TREE_INT_CST_LOW (byte_offset_cst)])); + = build_int_cst_type (TREE_TYPE (TREE_TYPE (string_cst)), char_val); return get_or_create_constant_svalue (char_cst); } return NULL; diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc index a26be707599..6ab917465d6 100644 --- a/gcc/analyzer/region-model.cc +++ b/gcc/analyzer/region-model.cc @@ -3648,7 +3648,22 @@ string_cst_has_null_terminator (tree string_cst, byte_offset_t *out_bytes_read) { gcc_assert (bytes.m_start_byte_offset >= 0); - gcc_assert (bytes.m_start_byte_offset < TREE_STRING_LENGTH (string_cst)); + + /* If we're beyond the string_cst, reads are unsuccessful. */ + if (tree cst_size = get_string_cst_size (string_cst)) + if (TREE_CODE (cst_size) == INTEGER_CST) + if (bytes.m_start_byte_offset >= TREE_INT_CST_LOW (cst_size)) + return tristate::unknown (); + + /* Assume all bytes after TREE_STRING_LENGTH are zero. This handles + the case where an array is initialized with a string_cst that isn't + as long as the array, where the remaining elements are + empty-initialized and thus zeroed. */ + if (bytes.m_start_byte_offset >= TREE_STRING_LENGTH (string_cst)) + { + *out_bytes_read = 1; + return tristate (true); + } /* Look for the first 0 byte within STRING_CST from START_READ_OFFSET onwards. */ diff --git a/gcc/testsuite/c-c++-common/analyzer/strlen-pr113999.c b/gcc/testsuite/c-c++-common/analyzer/strlen-pr113999.c new file mode 100644 index 00000000000..f822606415a --- /dev/null +++ b/gcc/testsuite/c-c++-common/analyzer/strlen-pr113999.c @@ -0,0 +1,8 @@ +int main() { + char a[20] = "ab"; + __builtin_strcpy(a, "123"); + long n0 = __builtin_strlen(a); + __builtin_strncpy(a + 3, a, n0); + __builtin_strlen(a); + return 0; +} diff --git a/gcc/testsuite/gcc.dg/analyzer/strlen-1.c b/gcc/testsuite/gcc.dg/analyzer/strlen-1.c index 99ce3aa297b..54e8ef1dd29 100644 --- a/gcc/testsuite/gcc.dg/analyzer/strlen-1.c +++ b/gcc/testsuite/gcc.dg/analyzer/strlen-1.c @@ -52,3 +52,55 @@ test_passthrough (const char *str) - complain if NULL str - should it be tainted if str's bytes are tainted? */ + +static size_t __attribute__((noinline)) +call_strlen_3 (const char *p) +{ + return __builtin_strlen (p); +} + +void test_array_initialization_from_shorter_literal (void) +{ + const char buf[10] = "abc"; + __analyzer_eval (call_strlen_3 (buf) == 3); /* { dg-warning "TRUE" } */ + __analyzer_eval (call_strlen_3 (buf + 5) == 0); /* { dg-warning "TRUE" } */ + __analyzer_eval (buf[5] == 0); /* { dg-warning "TRUE" } */ +} + +static size_t __attribute__((noinline)) +call_strlen_4 (const char *p) +{ + return __builtin_strlen (p); /* { dg-warning "stack-based buffer over-read" } */ +} + +char test_array_initialization_from_longer_literal (void) +{ + const char buf[3] = "abcdefg"; /* { dg-warning "initializer-string for array of 'char' is too long" } */ + __analyzer_eval (call_strlen_4 (buf) == 3); /* { dg-warning "UNKNOWN" } */ + return buf[5]; /* { dg-warning "stack-based buffer over-read" } */ +} + +static size_t __attribute__((noinline)) +call_strlen_5 (const char *p) +{ + return __builtin_strlen (p); +} + +static size_t __attribute__((noinline)) +call_strlen_5a (const char *p) +{ + return __builtin_strlen (p); /* { dg-warning "stack-based buffer over-read" } */ +} + +char test_array_initialization_implicit_length (void) +{ + const char buf[] = "abc"; + __analyzer_eval (call_strlen_5 (buf) == 3); /* { dg-warning "TRUE" } */ + __analyzer_eval (call_strlen_5 (buf + 2) == 1); /* { dg-warning "TRUE" } */ + __analyzer_eval (call_strlen_5 (buf + 3) == 0); /* { dg-warning "TRUE" } */ + __analyzer_eval (buf[0] == 'a'); /* { dg-warning "TRUE" } */ + __analyzer_eval (buf[3] == 0); /* { dg-warning "TRUE" } */ + __analyzer_eval (call_strlen_5a (buf + 4) == 0); /* { dg-warning "UNKNOWN" } */ + return buf[4]; /* { dg-warning "stack-based buffer over-read" } */ +} +