[Bug analyzer/105948] New: RFE: analyzer could check c++ placement-new sizes

[Bug analyzer/105948] New: RFE: analyzer could check c++ placement-new sizes

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105948

            Bug ID: 105948
           Summary: RFE: analyzer could check c++ placement-new sizes
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: dmalcolm at gcc dot gnu.org
            Blocks: 97110, 105887
  Target Milestone: ---

clang's static analyzer has:
 
https://clang.llvm.org/docs/analyzer/checkers.html#cplusplus-placementnewchecker-c

We should check that placement new's memory region is large enough (for both
static and dynamic allocation cases).


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97110
[Bug 97110] [meta-bug] tracker bug for supporting C++ in -fanalyzer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105887
[Bug 105887] [meta-bug] clang analyzer warnings that GCC's -fanalyzer could
implement

[Bug analyzer/105948] RFE: analyzer could check c++ placement-new sizes

[vultkayn at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105948

--- Comment #1 from Benjamin Priour <vultkayn at gcc dot gnu.org> ---
I'm writing a patch for this, and I've got support for non symbolic bounds.
However, as I wrote my patch, a missing warning came up.
Consider the test case:

---

void var_too_short ()
{
  short s;
  long *lp = new (&s) long; /* { dg-warning "stack-based buffer overflow" } */
  /* { dg-warning "allocated buffer size is not a multiple of the pointee's
size" "" { target *-*-* } .-1 } */
}

void static_buffer_too_short ()
{
  int n = 16;
  int buf[n];
  int *p = new (buf) int[n + 1]; /* { dg-warning "stack-based buffer overflow"
} */
  /* (+) */
}

---

In 'var_too_short', two warnings are emitted, second being from
'-Wanalyzer-allocation-size', which makes sense.

Then given the name of this warning, would it not also makes sense to emit it
at (+) in 'static_buffer_too_short' ?

Pointer 'p' is an int, and 'buf' is an array of int, so the buffer size is
indeed a multiple size of 'p'.

However, we know 'p' points to an area actually overflowing 'buf', so
-Wanalyzer-allocation-size is reasonable there.

What are your thoughts on that ?

[Bug analyzer/105948] RFE: analyzer could check c++ placement-new sizes

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105948

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Benjamin Priour <vultkayn@gcc.gnu.org>:

https://gcc.gnu.org/g:e7b267444045c507654a2a3f758efee5d5b550df

commit r14-3632-ge7b267444045c507654a2a3f758efee5d5b550df
Author: benjamin priour <priour.be@gmail.com>
Date:   Fri Sep 1 00:01:29 2023 +0200

    analyzer: Add support of placement new and improved operator new
[PR105948,PR94355]

    Fixed spurious possibly-NULL warning always tagging along throwing
    operator new despite it never returning NULL.
    Now operator new is correctly recognized as possibly returning NULL
    if and only if it is non-throwing or exceptions have been disabled.
    Different standard signatures of operator new are now properly
    recognized.

    Added support of placement new, so that it is now properly recognized,
    and a 'heap_allocated' region is no longer created for it.
    Placement new size is also checked and a 'Wanalyzer-allocation-size'
    is emitted when relevant, as well as always a 'Wanalyzer-out-of-bounds'.

    'operator new' non-throwing variants are detected y checking the types
    of the parameters.
    Indeed, in a call to new (std::nothrow) () the chosen overload
    has signature 'operator new (void*, std::nothrow_t&)', where the second
    parameter is a reference. In a placement new, the second parameter will
    always be a void pointer.

    Prior to this patch, some buffers first allocated with 'new', then deleted
    an thereafter used would result in a 'Wanalyzer-user-after-free'
    warning. However the wording was "use after 'free'" instead of the
    expected "use after 'delete'".
    This patch fixes this by introducing a new kind of poisoned value,
    namely POISON_KIND_DELETED.

    Due to how the analyzer sees calls to non-throwing variants of
    operator new, dereferencing a pointer freshly allocated in this fashion
    caused both a 'Wanalyzer-use-of-uninitialized-value' and a
    'Wanalyzer-null-dereference' to be emitted, while only the latter was
    relevant. As a result, 'null-dereference' now supersedes
    'use-of-uninitialized'.

    Signed-off-by: benjamin priour <vultkayn@gcc.gnu.org>

    gcc/analyzer/ChangeLog:

            PR analyzer/105948
            PR analyzer/94355
            * analyzer.h (is_placement_new_p): New declaration.
            * call-details.cc
            (call_details::deref_ptr_arg): New function.
            Dereference the argument at given index if possible.
            * call-details.h: Declaration of the above function.
            * kf-lang-cp.cc (is_placement_new_p): Returns true if the gcall
            is recognized as a placement new.
            (kf_operator_delete::impl_call_post): Unbinding a region and its
            descendents now poisons with POISON_KIND_DELETED.
            (register_known_functions_lang_cp): Known function "operator
            delete" is now registered only once independently of its number of
            arguments.
            * region-model.cc (region_model::eval_condition): Now
            recursively calls itself if any of the operand is wrapped in a
            cast.
            * sm-malloc.cc (malloc_state_machine::on_stmt):
            Add placement new recognition.
            * svalue.cc (poison_kind_to_str): Wording for the new PK.
            * svalue.h (enum poison_kind): Add value POISON_KIND_DELETED.

    gcc/testsuite/ChangeLog:

            PR analyzer/105948
            PR analyzer/94355
            * g++.dg/analyzer/out-of-bounds-placement-new.C: Added a directive.
            * g++.dg/analyzer/placement-new.C: Added tests.
            * g++.dg/analyzer/new-2.C: New test.
            * g++.dg/analyzer/noexcept-new.C: New test.
            * g++.dg/analyzer/placement-new-size.C: New test.

[Bug analyzer/105948] RFE: analyzer could check c++ placement-new sizes

[vultkayn at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105948

--- Comment #3 from Benjamin Priour <vultkayn at gcc dot gnu.org> ---
I believe the above patch resolves this PR.
I'm letting it sip in trunk for a few days before marking it as solved.