* [PATCH] c++: ICE with -fsanitize=vptr and constexpr dynamic_cast [PR98103]
@ 2020-12-02 23:18 Marek Polacek
2020-12-03 2:01 ` Jason Merrill
0 siblings, 1 reply; 4+ messages in thread
From: Marek Polacek @ 2020-12-02 23:18 UTC (permalink / raw)
To: Jason Merrill, GCC Patches
-fsanitize=vptr initializes all vtable pointers to null so that it can
catch invalid calls; see cp_ubsan_maybe_initialize_vtbl_ptrs. That
means that evaluating a vtable reference can produce a null pointer
in this mode, so cxx_eval_dynamic_cast_fn should check that.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
gcc/cp/ChangeLog:
PR c++/98103
* constexpr.c (cxx_eval_dynamic_cast_fn): If the evaluating of vtable
yields a null pointer, return.
gcc/testsuite/ChangeLog:
PR c++/98103
* g++.dg/ubsan/vptr-18.C: New test.
---
gcc/cp/constexpr.c | 4 +++-
gcc/testsuite/g++.dg/ubsan/vptr-18.C | 27 +++++++++++++++++++++++++++
2 files changed, 30 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/ubsan/vptr-18.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 9a1a1db1267..8c6a9cf2b40 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -1996,7 +1996,9 @@ cxx_eval_dynamic_cast_fn (const constexpr_ctx *ctx, tree call,
tree vtable = build_vfield_ref (obj, TREE_TYPE (obj));
vtable = cxx_eval_constant_expression (ctx, vtable, /*lval*/false,
non_constant_p, overflow_p);
- if (*non_constant_p)
+ /* With -fsanitize=vptr, we initialize all vtable pointers to null,
+ so it's possible that we got a null pointer now. */
+ if (*non_constant_p || integer_zerop (vtable))
return call;
/* VTABLE will be &_ZTV1A + 16 or similar, get _ZTV1A. */
vtable = extract_obj_from_addr_offset (vtable);
diff --git a/gcc/testsuite/g++.dg/ubsan/vptr-18.C b/gcc/testsuite/g++.dg/ubsan/vptr-18.C
new file mode 100644
index 00000000000..9f421c269bc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ubsan/vptr-18.C
@@ -0,0 +1,27 @@
+// PR c++/98103
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-fsanitize=vptr" }
+// Modified constexpr-dynamic17.C. -fsanitize=vptr initializes all vtable
+// pointers to null, so we don't get the "accessing uninitialized member"
+// error.
+
+struct V {
+ virtual void f();
+};
+
+struct A : V { };
+
+struct B : V {
+ constexpr B(V*, A*);
+};
+
+struct D : B, A {
+ constexpr D() : B((A*)this, this) { }
+};
+
+constexpr B::B(V* v, A* a)
+{
+ dynamic_cast<B*>(a);
+}
+
+constexpr D d;
base-commit: dc2b372ed1b1e9af6db45051cff95478c7616807
--
2.28.0
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] c++: ICE with -fsanitize=vptr and constexpr dynamic_cast [PR98103]
2020-12-02 23:18 [PATCH] c++: ICE with -fsanitize=vptr and constexpr dynamic_cast [PR98103] Marek Polacek
@ 2020-12-03 2:01 ` Jason Merrill
2020-12-05 3:40 ` Marek Polacek
0 siblings, 1 reply; 4+ messages in thread
From: Jason Merrill @ 2020-12-03 2:01 UTC (permalink / raw)
To: Marek Polacek, GCC Patches
On 12/2/20 6:18 PM, Marek Polacek wrote:
> -fsanitize=vptr initializes all vtable pointers to null so that it can
> catch invalid calls; see cp_ubsan_maybe_initialize_vtbl_ptrs. That
> means that evaluating a vtable reference can produce a null pointer
> in this mode, so cxx_eval_dynamic_cast_fn should check that.
Yes, but we shouldn't accept it silently; sanitize is supposed to flag
undefined behavior, not allow it. If we see a null vptr, we should
complain and set *non_constant_p.
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>
> gcc/cp/ChangeLog:
>
> PR c++/98103
> * constexpr.c (cxx_eval_dynamic_cast_fn): If the evaluating of vtable
> yields a null pointer, return.
>
> gcc/testsuite/ChangeLog:
>
> PR c++/98103
> * g++.dg/ubsan/vptr-18.C: New test.
> ---
> gcc/cp/constexpr.c | 4 +++-
> gcc/testsuite/g++.dg/ubsan/vptr-18.C | 27 +++++++++++++++++++++++++++
> 2 files changed, 30 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/g++.dg/ubsan/vptr-18.C
>
> diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
> index 9a1a1db1267..8c6a9cf2b40 100644
> --- a/gcc/cp/constexpr.c
> +++ b/gcc/cp/constexpr.c
> @@ -1996,7 +1996,9 @@ cxx_eval_dynamic_cast_fn (const constexpr_ctx *ctx, tree call,
> tree vtable = build_vfield_ref (obj, TREE_TYPE (obj));
> vtable = cxx_eval_constant_expression (ctx, vtable, /*lval*/false,
> non_constant_p, overflow_p);
> - if (*non_constant_p)
> + /* With -fsanitize=vptr, we initialize all vtable pointers to null,
> + so it's possible that we got a null pointer now. */
> + if (*non_constant_p || integer_zerop (vtable))
> return call;
> /* VTABLE will be &_ZTV1A + 16 or similar, get _ZTV1A. */
> vtable = extract_obj_from_addr_offset (vtable);
> diff --git a/gcc/testsuite/g++.dg/ubsan/vptr-18.C b/gcc/testsuite/g++.dg/ubsan/vptr-18.C
> new file mode 100644
> index 00000000000..9f421c269bc
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/ubsan/vptr-18.C
> @@ -0,0 +1,27 @@
> +// PR c++/98103
> +// { dg-do compile { target c++20 } }
> +// { dg-additional-options "-fsanitize=vptr" }
> +// Modified constexpr-dynamic17.C. -fsanitize=vptr initializes all vtable
> +// pointers to null, so we don't get the "accessing uninitialized member"
> +// error.
> +
> +struct V {
> + virtual void f();
> +};
> +
> +struct A : V { };
> +
> +struct B : V {
> + constexpr B(V*, A*);
> +};
> +
> +struct D : B, A {
> + constexpr D() : B((A*)this, this) { }
> +};
> +
> +constexpr B::B(V* v, A* a)
> +{
> + dynamic_cast<B*>(a);
> +}
> +
> +constexpr D d;
>
> base-commit: dc2b372ed1b1e9af6db45051cff95478c7616807
>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] c++: ICE with -fsanitize=vptr and constexpr dynamic_cast [PR98103]
2020-12-03 2:01 ` Jason Merrill
@ 2020-12-05 3:40 ` Marek Polacek
2020-12-08 21:50 ` Jason Merrill
0 siblings, 1 reply; 4+ messages in thread
From: Marek Polacek @ 2020-12-05 3:40 UTC (permalink / raw)
To: Jason Merrill; +Cc: GCC Patches
On Wed, Dec 02, 2020 at 09:01:48PM -0500, Jason Merrill wrote:
> On 12/2/20 6:18 PM, Marek Polacek wrote:
> > -fsanitize=vptr initializes all vtable pointers to null so that it can
> > catch invalid calls; see cp_ubsan_maybe_initialize_vtbl_ptrs. That
> > means that evaluating a vtable reference can produce a null pointer
> > in this mode, so cxx_eval_dynamic_cast_fn should check that.
>
> Yes, but we shouldn't accept it silently; sanitize is supposed to flag
> undefined behavior, not allow it. If we see a null vptr, we should complain
> and set *non_constant_p.
True, I shouldn't have left it for the run-time diagnostic. How's this, then?
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
-fsanitize=vptr initializes all vtable pointers to null so that it can
catch invalid calls; see cp_ubsan_maybe_initialize_vtbl_ptrs. That
means that evaluating a vtable reference can produce a null pointer
in this mode, so cxx_eval_dynamic_cast_fn should check that and give
and error.
gcc/cp/ChangeLog:
PR c++/98103
* constexpr.c (cxx_eval_dynamic_cast_fn): If the evaluating of vtable
yields a null pointer, give an error and return. Use objtype.
gcc/testsuite/ChangeLog:
PR c++/98103
* g++.dg/ubsan/vptr-18.C: New test.
---
gcc/cp/constexpr.c | 11 ++++++++++-
gcc/testsuite/g++.dg/ubsan/vptr-18.C | 25 +++++++++++++++++++++++++
2 files changed, 35 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/ubsan/vptr-18.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index e0d358027c9..c413313fbe1 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -1998,11 +1998,20 @@ cxx_eval_dynamic_cast_fn (const constexpr_ctx *ctx, tree call,
to the object under construction or destruction, this object is
considered to be a most derived object that has the type of the
constructor or destructor's class. */
- tree vtable = build_vfield_ref (obj, TREE_TYPE (obj));
+ tree vtable = build_vfield_ref (obj, objtype);
vtable = cxx_eval_constant_expression (ctx, vtable, /*lval*/false,
non_constant_p, overflow_p);
if (*non_constant_p)
return call;
+ /* With -fsanitize=vptr, we initialize all vtable pointers to null,
+ so it's possible that we got a null pointer now. */
+ if (integer_zerop (vtable))
+ {
+ if (!ctx->quiet)
+ error_at (loc, "virtual table pointer is used uninitialized");
+ *non_constant_p = true;
+ return integer_zero_node;
+ }
/* VTABLE will be &_ZTV1A + 16 or similar, get _ZTV1A. */
vtable = extract_obj_from_addr_offset (vtable);
const tree mdtype = DECL_CONTEXT (vtable);
diff --git a/gcc/testsuite/g++.dg/ubsan/vptr-18.C b/gcc/testsuite/g++.dg/ubsan/vptr-18.C
new file mode 100644
index 00000000000..cd2ca0a9fb6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ubsan/vptr-18.C
@@ -0,0 +1,25 @@
+// PR c++/98103
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-fsanitize=vptr -fno-sanitize-recover=vptr" }
+// Modified constexpr-dynamic17.C.
+
+struct V {
+ virtual void f();
+};
+
+struct A : V { };
+
+struct B : V {
+ constexpr B(V*, A*);
+};
+
+struct D : B, A {
+ constexpr D() : B((A*)this, this) { }
+};
+
+constexpr B::B(V* v, A* a)
+{
+ dynamic_cast<B*>(a); // { dg-error "uninitialized" }
+}
+
+constexpr D d;
base-commit: df933e307b1950ce12472660dcac1765b8eb431d
--
2.28.0
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] c++: ICE with -fsanitize=vptr and constexpr dynamic_cast [PR98103]
2020-12-05 3:40 ` Marek Polacek
@ 2020-12-08 21:50 ` Jason Merrill
0 siblings, 0 replies; 4+ messages in thread
From: Jason Merrill @ 2020-12-08 21:50 UTC (permalink / raw)
To: Marek Polacek; +Cc: GCC Patches
On 12/4/20 10:40 PM, Marek Polacek wrote:
> On Wed, Dec 02, 2020 at 09:01:48PM -0500, Jason Merrill wrote:
>> On 12/2/20 6:18 PM, Marek Polacek wrote:
>>> -fsanitize=vptr initializes all vtable pointers to null so that it can
>>> catch invalid calls; see cp_ubsan_maybe_initialize_vtbl_ptrs. That
>>> means that evaluating a vtable reference can produce a null pointer
>>> in this mode, so cxx_eval_dynamic_cast_fn should check that.
>>
>> Yes, but we shouldn't accept it silently; sanitize is supposed to flag
>> undefined behavior, not allow it. If we see a null vptr, we should complain
>> and set *non_constant_p.
>
> True, I shouldn't have left it for the run-time diagnostic. How's this, then?
>
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
OK.
> -- >8 --
> -fsanitize=vptr initializes all vtable pointers to null so that it can
> catch invalid calls; see cp_ubsan_maybe_initialize_vtbl_ptrs. That
> means that evaluating a vtable reference can produce a null pointer
> in this mode, so cxx_eval_dynamic_cast_fn should check that and give
> and error.
>
> gcc/cp/ChangeLog:
>
> PR c++/98103
> * constexpr.c (cxx_eval_dynamic_cast_fn): If the evaluating of vtable
> yields a null pointer, give an error and return. Use objtype.
>
> gcc/testsuite/ChangeLog:
>
> PR c++/98103
> * g++.dg/ubsan/vptr-18.C: New test.
> ---
> gcc/cp/constexpr.c | 11 ++++++++++-
> gcc/testsuite/g++.dg/ubsan/vptr-18.C | 25 +++++++++++++++++++++++++
> 2 files changed, 35 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/g++.dg/ubsan/vptr-18.C
>
> diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
> index e0d358027c9..c413313fbe1 100644
> --- a/gcc/cp/constexpr.c
> +++ b/gcc/cp/constexpr.c
> @@ -1998,11 +1998,20 @@ cxx_eval_dynamic_cast_fn (const constexpr_ctx *ctx, tree call,
> to the object under construction or destruction, this object is
> considered to be a most derived object that has the type of the
> constructor or destructor's class. */
> - tree vtable = build_vfield_ref (obj, TREE_TYPE (obj));
> + tree vtable = build_vfield_ref (obj, objtype);
> vtable = cxx_eval_constant_expression (ctx, vtable, /*lval*/false,
> non_constant_p, overflow_p);
> if (*non_constant_p)
> return call;
> + /* With -fsanitize=vptr, we initialize all vtable pointers to null,
> + so it's possible that we got a null pointer now. */
> + if (integer_zerop (vtable))
> + {
> + if (!ctx->quiet)
> + error_at (loc, "virtual table pointer is used uninitialized");
> + *non_constant_p = true;
> + return integer_zero_node;
> + }
> /* VTABLE will be &_ZTV1A + 16 or similar, get _ZTV1A. */
> vtable = extract_obj_from_addr_offset (vtable);
> const tree mdtype = DECL_CONTEXT (vtable);
> diff --git a/gcc/testsuite/g++.dg/ubsan/vptr-18.C b/gcc/testsuite/g++.dg/ubsan/vptr-18.C
> new file mode 100644
> index 00000000000..cd2ca0a9fb6
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/ubsan/vptr-18.C
> @@ -0,0 +1,25 @@
> +// PR c++/98103
> +// { dg-do compile { target c++20 } }
> +// { dg-additional-options "-fsanitize=vptr -fno-sanitize-recover=vptr" }
> +// Modified constexpr-dynamic17.C.
> +
> +struct V {
> + virtual void f();
> +};
> +
> +struct A : V { };
> +
> +struct B : V {
> + constexpr B(V*, A*);
> +};
> +
> +struct D : B, A {
> + constexpr D() : B((A*)this, this) { }
> +};
> +
> +constexpr B::B(V* v, A* a)
> +{
> + dynamic_cast<B*>(a); // { dg-error "uninitialized" }
> +}
> +
> +constexpr D d;
>
> base-commit: df933e307b1950ce12472660dcac1765b8eb431d
>
^ permalink raw reply [flat|nested] 4+ messages in thread
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2020-12-02 23:18 [PATCH] c++: ICE with -fsanitize=vptr and constexpr dynamic_cast [PR98103] Marek Polacek
2020-12-03 2:01 ` Jason Merrill
2020-12-05 3:40 ` Marek Polacek
2020-12-08 21:50 ` Jason Merrill
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