From e2f014fcefcd2ad56b31995329820bbd99072eae Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Fri, 27 May 2022 11:40:42 +0200 Subject: [PATCH] fold-const: Fix up -fsanitize=null in C++ [PR105729] The following testcase triggers a false positive UBSan binding a reference to null diagnostics. In the FE we instrument conversions from pointer to reference type to diagnose at runtime if the operand of such a conversion is 0. The problem is that a GENERIC folding folds ((const struct Bar *) ((const struct Foo *) this)->data) + (sizetype) range_check (x) conversion to const struct Bar & by converting to that the first operand of the POINTER_PLUS_EXPR. But that changes when the -fsanitize=null binding to reference runtime check occurs. Without the optimization, it is invoked on the result of the POINTER_PLUS_EXPR, and as range_check call throws, that means it never triggers in the testcase. With the optimization, it checks whether this->data is NULL and it is. The following patch avoids that optimization during GENERIC folding when -fsanitize=null is enabled and it is a cast from non-REFERENCE_TYPE to REFERENCE_TYPE. 2022-05-27 Jakub Jelinek PR sanitizer/105729 * fold-const.cc (fold_unary_loc): Don't optimize (X &) ((Y *) z + w) to (X &) z + w if -fsanitize=null during GENERIC folding. * g++.dg/ubsan/pr105729.C: New test. --- gcc/fold-const.cc | 10 ++++++++++ gcc/testsuite/g++.dg/ubsan/pr105729.C | 29 +++++++++++++++++++++++++++++ 2 files changed, 39 insertions(+) create mode 100644 gcc/testsuite/g++.dg/ubsan/pr105729.C diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc index 7bf1231..fbdf3c8 100644 --- a/gcc/fold-const.cc +++ b/gcc/fold-const.cc @@ -9516,6 +9516,16 @@ fold_unary_loc (location_t loc, enum tree_code code, tree type, tree op0) > min_align_of_type (TREE_TYPE (TREE_TYPE (arg00))))) return NULL_TREE; + /* Similarly, avoid this optimization in GENERIC for -fsanitize=null + when type is a reference type and arg00's type is not, + because arg00 could be validly nullptr and if arg01 doesn't return, + we don't want false positive binding of reference to nullptr. */ + if (TREE_CODE (type) == REFERENCE_TYPE + && !in_gimple_form + && sanitize_flags_p (SANITIZE_NULL) + && TREE_CODE (TREE_TYPE (arg00)) != REFERENCE_TYPE) + return NULL_TREE; + arg00 = fold_convert_loc (loc, type, arg00); return fold_build_pointer_plus_loc (loc, arg00, arg01); } diff --git a/gcc/testsuite/g++.dg/ubsan/pr105729.C b/gcc/testsuite/g++.dg/ubsan/pr105729.C new file mode 100644 index 0000000..fb67663 --- /dev/null +++ b/gcc/testsuite/g++.dg/ubsan/pr105729.C @@ -0,0 +1,29 @@ +// PR sanitizer/105729 +// { dg-do run } +// { dg-options "-fsanitize=null -fno-sanitize-recover=null" } + +int +foo (int x) +{ + throw 0; +} + +struct S {}; +struct T { + S *data; + T () : data (0) {} + const S &bar (int x) const { return data[foo (x)]; } +}; + +int +main () +{ + T t; + try + { + t.bar (-1); + } + catch (...) + { + } +} -- 2.7.4