Re: [PATCH] extend -Wstringop-overflow to allocated objects (PR 91582)
On 12/6/19 8:44 AM, Christophe Lyon wrote:
On Thu, 5 Dec 2019 at 02:37, Martin Sebor wrote:
On 12/2/19 10:06 AM, Jeff Law wrote:
On 11/8/19 3:11 PM, Martin Sebor wrote:
Unless it's used with _FORTIFY_SOURCE, -Wstringop-overflow
doesn't consider out-of-bounds accesses to objects allocated
by alloca, malloc, other functions declared with attribute
alloc_size, or even VLAs with variable bounds. This was
a known limitation of the checks (done just before expansion)
relying on the the object size pass when they were introduced
in GCC 7.
But since its introduction in GCC 7, the warning has evolved
beyond some of the limitations of the object size pass. Unlike
it, the warning considers non-constant offsets and stores with
non-constant sizes. Attached is a simple enhancement that
(finally) adds the ability to also detect overflow in allocated
objects to the warning.
With the patch GCC detects the overflow in code like this:
char* f (void)
{
char s[] = "12345";
char *p = malloc (strlen (s));
strcpy (p, s); // warning here
return p;
}
but not (yet) in something like this:
char* g (const char *s)
{
char *p = malloc (strlen (s));
strcpy (p, s); // no warning (yet)
return p;
}
and quite a few other examples. Doing better requires extending
the strlen pass. I'm working on this extension and expect to
submit a patch before stage 1 ends.
Martin
PS I was originally planning to do all the allocation checking
in the strlen pass but it occurred to me that by also enhancing
the compute_objsize function, all warnings that use it will
benefit. Besides -Wstringop-overflow this includes a subset
of -Warray-bounds, -Wformat-overflow, and -Wrestrict. It's
nice when a small enhancement has such a broad positive effect.
PR middle-end/91582 - missing heap overflow detection for strcpy
gcc/ChangeLog:
* builtins.c (gimple_call_alloc_size): New function.
(compute_objsize): Add argument. Call gimple_call_alloc_size.
Handle variable offsets and indices.
* builtins.h (gimple_call_alloc_size): Declare.
(compute_objsize): Add argument.
* tree-ssa-strlen.c (handle_store): Handle calls to allocated objects.
gcc/testsuite/ChangeLog:
* c-c++-common/Wstringop-truncation.c: Remove xfails.
* gcc/testsuite/g++.dg/ext/attr-alloc_size.C: Suppress -Warray-bounds.
* gcc.dg/Wstringop-overflow-22.c: New test.
* gcc/testsuite/gcc.dg/attr-alloc_size.c: Suppress -Warray-bounds.
* gcc/testsuite/gcc.dg/attr-copy-2.c: Same.
* gcc.dg/builtin-stringop-chk-5.c: Remove xfails.
* gcc.dg/builtin-stringop-chk-8.c: Same. Correct the text of expected
warnings.
* gcc.target/i386/pr82002-2a.c: Prune expected warning.
* gcc.target/i386/pr82002-2b.c: Same.
[ ... ]
Index: gcc/builtins.c
===
--- gcc/builtins.c (revision 277978)
+++ gcc/builtins.c (working copy)
@@ -3563,6 +3563,80 @@ check_access (tree exp, tree, tree, tree dstwrite,
return true;
}
+/* If STMT is a call to an allocation function, returns the size
+ of the object allocated by the call. */
+
+tree
+gimple_call_alloc_size (gimple *stmt)
+{
+ tree size = gimple_call_arg (stmt, argidx1);
+ tree n = argidx2 < nargs ? gimple_call_arg (stmt, argidx2) :
integer_one_node;
+
+ /* To handle ranges do the math in wide_int and return the product
+ of the upper bounds as a constant. Ignore anti-ranges. */
+ wide_int rng1[2];
+ if (TREE_CODE (size) == INTEGER_CST)
+rng1[0] = rng1[1] = wi::to_wide (size);
+ else if (TREE_CODE (size) != SSA_NAME
+ || get_range_info (size, rng1, rng1 + 1) != VR_RANGE)
+return NULL_TREE;
+
+ wide_int rng2[2];
+ if (TREE_CODE (n) == INTEGER_CST)
+rng2[0] = rng2[1] = wi::to_wide (n);
+ else if (TREE_CODE (n) != SSA_NAME
+ || get_range_info (n, rng2 + 1, rng2 + 1) != VR_RANGE)
+return NULL_TREE;
Should that 2nd call to get_range_info be "get_range_info (n, rng2, rng2
+ 1)? I don't think it makes any difference in practice due to the
implementation of get_range_info, but if it wasn't intentional let's get
it fixed.
Yes, it should be. It's correct in my tree but didn't post
the updated revision.
Index: gcc/builtins.h
===
--- gcc/builtins.h (revision 277978)
+++ gcc/builtins.h (working copy)
@@ -134,7 +134,8 @@ extern tree fold_call_stmt (gcall *, bool);
extern void set_builtin_user_assembler_name (tree decl, const char *asmspec);
extern bool is_simple_builtin (tree);
extern bool is_inexpensive_builtin (tree);
-extern tree compute_objsize (tree, int, tree * = NULL);
+tree gimple_call_alloc_size (gimple *);
+extern tree compute_objsize (tree, int, tree * = NULL, tree * = NULL);
extern bool readonly_data_expr (tree
Re: [PATCH] extend -Wstringop-overflow to allocated objects (PR 91582)
On Thu, 5 Dec 2019 at 02:37, Martin Sebor wrote:
>
> On 12/2/19 10:06 AM, Jeff Law wrote:
> > On 11/8/19 3:11 PM, Martin Sebor wrote:
> >> Unless it's used with _FORTIFY_SOURCE, -Wstringop-overflow
> >> doesn't consider out-of-bounds accesses to objects allocated
> >> by alloca, malloc, other functions declared with attribute
> >> alloc_size, or even VLAs with variable bounds. This was
> >> a known limitation of the checks (done just before expansion)
> >> relying on the the object size pass when they were introduced
> >> in GCC 7.
> >>
> >> But since its introduction in GCC 7, the warning has evolved
> >> beyond some of the limitations of the object size pass. Unlike
> >> it, the warning considers non-constant offsets and stores with
> >> non-constant sizes. Attached is a simple enhancement that
> >> (finally) adds the ability to also detect overflow in allocated
> >> objects to the warning.
> >>
> >> With the patch GCC detects the overflow in code like this:
> >>
> >>char* f (void)
> >>{
> >> char s[] = "12345";
> >> char *p = malloc (strlen (s));
> >> strcpy (p, s); // warning here
> >> return p;
> >>}
> >>
> >> but not (yet) in something like this:
> >>
> >>char* g (const char *s)
> >>{
> >> char *p = malloc (strlen (s));
> >> strcpy (p, s); // no warning (yet)
> >> return p;
> >>}
> >>
> >> and quite a few other examples. Doing better requires extending
> >> the strlen pass. I'm working on this extension and expect to
> >> submit a patch before stage 1 ends.
> >>
> >> Martin
> >>
> >> PS I was originally planning to do all the allocation checking
> >> in the strlen pass but it occurred to me that by also enhancing
> >> the compute_objsize function, all warnings that use it will
> >> benefit. Besides -Wstringop-overflow this includes a subset
> >> of -Warray-bounds, -Wformat-overflow, and -Wrestrict. It's
> >> nice when a small enhancement has such a broad positive effect.
> >
> >> PR middle-end/91582 - missing heap overflow detection for strcpy
> >>
> >> gcc/ChangeLog:
> >>
> >> * builtins.c (gimple_call_alloc_size): New function.
> >> (compute_objsize): Add argument. Call gimple_call_alloc_size.
> >> Handle variable offsets and indices.
> >> * builtins.h (gimple_call_alloc_size): Declare.
> >> (compute_objsize): Add argument.
> >> * tree-ssa-strlen.c (handle_store): Handle calls to allocated
> >> objects.
> >>
> >> gcc/testsuite/ChangeLog:
> >>
> >> * c-c++-common/Wstringop-truncation.c: Remove xfails.
> >> * gcc/testsuite/g++.dg/ext/attr-alloc_size.C: Suppress
> >> -Warray-bounds.
> >> * gcc.dg/Wstringop-overflow-22.c: New test.
> >> * gcc/testsuite/gcc.dg/attr-alloc_size.c: Suppress -Warray-bounds.
> >> * gcc/testsuite/gcc.dg/attr-copy-2.c: Same.
> >> * gcc.dg/builtin-stringop-chk-5.c: Remove xfails.
> >> * gcc.dg/builtin-stringop-chk-8.c: Same. Correct the text of
> >> expected
> >> warnings.
> >> * gcc.target/i386/pr82002-2a.c: Prune expected warning.
> >> * gcc.target/i386/pr82002-2b.c: Same.
> > [ ... ]
> >
> >
> >> Index: gcc/builtins.c
> >> ===
> >> --- gcc/builtins.c (revision 277978)
> >> +++ gcc/builtins.c (working copy)
> >> @@ -3563,6 +3563,80 @@ check_access (tree exp, tree, tree, tree dstwrite,
> >> return true;
> >> }
> >>
> >> +/* If STMT is a call to an allocation function, returns the size
> >> + of the object allocated by the call. */
> >> +
> >> +tree
> >> +gimple_call_alloc_size (gimple *stmt)
> >> +{
> >> + tree size = gimple_call_arg (stmt, argidx1);
> >> + tree n = argidx2 < nargs ? gimple_call_arg (stmt, argidx2) :
> >> integer_one_node;
> >> +
> >> + /* To handle ranges do the math in wide_int and return the product
> >> + of the upper bounds as a constant. Ignore anti-ranges. */
> >> + wide_int rng1[2];
> >> + if (TREE_CODE (size) == INTEGER_CST)
> >> +rng1[0] = rng1[1] = wi::to_wide (size);
> >> + else if (TREE_CODE (size) != SSA_NAME
> >> + || get_range_info (size, rng1, rng1 + 1) != VR_RANGE)
> >> +return NULL_TREE;
> >> +
> >> + wide_int rng2[2];
> >> + if (TREE_CODE (n) == INTEGER_CST)
> >> +rng2[0] = rng2[1] = wi::to_wide (n);
> >> + else if (TREE_CODE (n) != SSA_NAME
> >> + || get_range_info (n, rng2 + 1, rng2 + 1) != VR_RANGE)
> >> +return NULL_TREE;
> > Should that 2nd call to get_range_info be "get_range_info (n, rng2, rng2
> > + 1)? I don't think it makes any difference in practice due to the
> > implementation of get_range_info, but if it wasn't intentional let's get
> > it fixed.
>
> Yes, it should be. It's correct in my tree but didn't post
> the updated revision.
>
> >
> >
> >> Index: gcc/builtins.h
> >> ===
> >> --- gcc/builtins.h (revision
Re: [PATCH] extend -Wstringop-overflow to allocated objects (PR 91582)
On 12/2/19 10:06 AM, Jeff Law wrote:
On 11/8/19 3:11 PM, Martin Sebor wrote:
Unless it's used with _FORTIFY_SOURCE, -Wstringop-overflow
doesn't consider out-of-bounds accesses to objects allocated
by alloca, malloc, other functions declared with attribute
alloc_size, or even VLAs with variable bounds. This was
a known limitation of the checks (done just before expansion)
relying on the the object size pass when they were introduced
in GCC 7.
But since its introduction in GCC 7, the warning has evolved
beyond some of the limitations of the object size pass. Unlike
it, the warning considers non-constant offsets and stores with
non-constant sizes. Attached is a simple enhancement that
(finally) adds the ability to also detect overflow in allocated
objects to the warning.
With the patch GCC detects the overflow in code like this:
char* f (void)
{
char s[] = "12345";
char *p = malloc (strlen (s));
strcpy (p, s); // warning here
return p;
}
but not (yet) in something like this:
char* g (const char *s)
{
char *p = malloc (strlen (s));
strcpy (p, s); // no warning (yet)
return p;
}
and quite a few other examples. Doing better requires extending
the strlen pass. I'm working on this extension and expect to
submit a patch before stage 1 ends.
Martin
PS I was originally planning to do all the allocation checking
in the strlen pass but it occurred to me that by also enhancing
the compute_objsize function, all warnings that use it will
benefit. Besides -Wstringop-overflow this includes a subset
of -Warray-bounds, -Wformat-overflow, and -Wrestrict. It's
nice when a small enhancement has such a broad positive effect.
PR middle-end/91582 - missing heap overflow detection for strcpy
gcc/ChangeLog:
* builtins.c (gimple_call_alloc_size): New function.
(compute_objsize): Add argument. Call gimple_call_alloc_size.
Handle variable offsets and indices.
* builtins.h (gimple_call_alloc_size): Declare.
(compute_objsize): Add argument.
* tree-ssa-strlen.c (handle_store): Handle calls to allocated objects.
gcc/testsuite/ChangeLog:
* c-c++-common/Wstringop-truncation.c: Remove xfails.
* gcc/testsuite/g++.dg/ext/attr-alloc_size.C: Suppress -Warray-bounds.
* gcc.dg/Wstringop-overflow-22.c: New test.
* gcc/testsuite/gcc.dg/attr-alloc_size.c: Suppress -Warray-bounds.
* gcc/testsuite/gcc.dg/attr-copy-2.c: Same.
* gcc.dg/builtin-stringop-chk-5.c: Remove xfails.
* gcc.dg/builtin-stringop-chk-8.c: Same. Correct the text of expected
warnings.
* gcc.target/i386/pr82002-2a.c: Prune expected warning.
* gcc.target/i386/pr82002-2b.c: Same.
[ ... ]
Index: gcc/builtins.c
===
--- gcc/builtins.c (revision 277978)
+++ gcc/builtins.c (working copy)
@@ -3563,6 +3563,80 @@ check_access (tree exp, tree, tree, tree dstwrite,
return true;
}
+/* If STMT is a call to an allocation function, returns the size
+ of the object allocated by the call. */
+
+tree
+gimple_call_alloc_size (gimple *stmt)
+{
+ tree size = gimple_call_arg (stmt, argidx1);
+ tree n = argidx2 < nargs ? gimple_call_arg (stmt, argidx2) :
integer_one_node;
+
+ /* To handle ranges do the math in wide_int and return the product
+ of the upper bounds as a constant. Ignore anti-ranges. */
+ wide_int rng1[2];
+ if (TREE_CODE (size) == INTEGER_CST)
+rng1[0] = rng1[1] = wi::to_wide (size);
+ else if (TREE_CODE (size) != SSA_NAME
+ || get_range_info (size, rng1, rng1 + 1) != VR_RANGE)
+return NULL_TREE;
+
+ wide_int rng2[2];
+ if (TREE_CODE (n) == INTEGER_CST)
+rng2[0] = rng2[1] = wi::to_wide (n);
+ else if (TREE_CODE (n) != SSA_NAME
+ || get_range_info (n, rng2 + 1, rng2 + 1) != VR_RANGE)
+return NULL_TREE;
Should that 2nd call to get_range_info be "get_range_info (n, rng2, rng2
+ 1)? I don't think it makes any difference in practice due to the
implementation of get_range_info, but if it wasn't intentional let's get
it fixed.
Yes, it should be. It's correct in my tree but didn't post
the updated revision.
Index: gcc/builtins.h
===
--- gcc/builtins.h (revision 277978)
+++ gcc/builtins.h (working copy)
@@ -134,7 +134,8 @@ extern tree fold_call_stmt (gcall *, bool);
extern void set_builtin_user_assembler_name (tree decl, const char *asmspec);
extern bool is_simple_builtin (tree);
extern bool is_inexpensive_builtin (tree);
-extern tree compute_objsize (tree, int, tree * = NULL);
+tree gimple_call_alloc_size (gimple *);
+extern tree compute_objsize (tree, int, tree * = NULL, tree * = NULL);
extern bool readonly_data_expr (tree exp);
extern bool init_target_chars (void);
Is there a reason there's no "extern" on the gimple_call_alloc_size
prototype?
I'm
Re: [PATCH] extend -Wstringop-overflow to allocated objects (PR 91582)
On 11/8/19 3:11 PM, Martin Sebor wrote:
> Unless it's used with _FORTIFY_SOURCE, -Wstringop-overflow
> doesn't consider out-of-bounds accesses to objects allocated
> by alloca, malloc, other functions declared with attribute
> alloc_size, or even VLAs with variable bounds. This was
> a known limitation of the checks (done just before expansion)
> relying on the the object size pass when they were introduced
> in GCC 7.
>
> But since its introduction in GCC 7, the warning has evolved
> beyond some of the limitations of the object size pass. Unlike
> it, the warning considers non-constant offsets and stores with
> non-constant sizes. Attached is a simple enhancement that
> (finally) adds the ability to also detect overflow in allocated
> objects to the warning.
>
> With the patch GCC detects the overflow in code like this:
>
> char* f (void)
> {
> char s[] = "12345";
> char *p = malloc (strlen (s));
> strcpy (p, s); // warning here
> return p;
> }
>
> but not (yet) in something like this:
>
> char* g (const char *s)
> {
> char *p = malloc (strlen (s));
> strcpy (p, s); // no warning (yet)
> return p;
> }
>
> and quite a few other examples. Doing better requires extending
> the strlen pass. I'm working on this extension and expect to
> submit a patch before stage 1 ends.
>
> Martin
>
> PS I was originally planning to do all the allocation checking
> in the strlen pass but it occurred to me that by also enhancing
> the compute_objsize function, all warnings that use it will
> benefit. Besides -Wstringop-overflow this includes a subset
> of -Warray-bounds, -Wformat-overflow, and -Wrestrict. It's
> nice when a small enhancement has such a broad positive effect.
> PR middle-end/91582 - missing heap overflow detection for strcpy
>
> gcc/ChangeLog:
>
> * builtins.c (gimple_call_alloc_size): New function.
> (compute_objsize): Add argument. Call gimple_call_alloc_size.
> Handle variable offsets and indices.
> * builtins.h (gimple_call_alloc_size): Declare.
> (compute_objsize): Add argument.
> * tree-ssa-strlen.c (handle_store): Handle calls to allocated objects.
>
> gcc/testsuite/ChangeLog:
>
> * c-c++-common/Wstringop-truncation.c: Remove xfails.
> * gcc/testsuite/g++.dg/ext/attr-alloc_size.C: Suppress -Warray-bounds.
> * gcc.dg/Wstringop-overflow-22.c: New test.
> * gcc/testsuite/gcc.dg/attr-alloc_size.c: Suppress -Warray-bounds.
> * gcc/testsuite/gcc.dg/attr-copy-2.c: Same.
> * gcc.dg/builtin-stringop-chk-5.c: Remove xfails.
> * gcc.dg/builtin-stringop-chk-8.c: Same. Correct the text of expected
> warnings.
> * gcc.target/i386/pr82002-2a.c: Prune expected warning.
> * gcc.target/i386/pr82002-2b.c: Same.
[ ... ]
> Index: gcc/builtins.c
> ===
> --- gcc/builtins.c (revision 277978)
> +++ gcc/builtins.c (working copy)
> @@ -3563,6 +3563,80 @@ check_access (tree exp, tree, tree, tree dstwrite,
>return true;
> }
>
> +/* If STMT is a call to an allocation function, returns the size
> + of the object allocated by the call. */
> +
> +tree
> +gimple_call_alloc_size (gimple *stmt)
> +{
> + tree size = gimple_call_arg (stmt, argidx1);
> + tree n = argidx2 < nargs ? gimple_call_arg (stmt, argidx2) :
> integer_one_node;
> +
> + /* To handle ranges do the math in wide_int and return the product
> + of the upper bounds as a constant. Ignore anti-ranges. */
> + wide_int rng1[2];
> + if (TREE_CODE (size) == INTEGER_CST)
> +rng1[0] = rng1[1] = wi::to_wide (size);
> + else if (TREE_CODE (size) != SSA_NAME
> + || get_range_info (size, rng1, rng1 + 1) != VR_RANGE)
> +return NULL_TREE;
> +
> + wide_int rng2[2];
> + if (TREE_CODE (n) == INTEGER_CST)
> +rng2[0] = rng2[1] = wi::to_wide (n);
> + else if (TREE_CODE (n) != SSA_NAME
> + || get_range_info (n, rng2 + 1, rng2 + 1) != VR_RANGE)
> +return NULL_TREE;
Should that 2nd call to get_range_info be "get_range_info (n, rng2, rng2
+ 1)? I don't think it makes any difference in practice due to the
implementation of get_range_info, but if it wasn't intentional let's get
it fixed.
> Index: gcc/builtins.h
> ===
> --- gcc/builtins.h (revision 277978)
> +++ gcc/builtins.h (working copy)
> @@ -134,7 +134,8 @@ extern tree fold_call_stmt (gcall *, bool);
> extern void set_builtin_user_assembler_name (tree decl, const char *asmspec);
> extern bool is_simple_builtin (tree);
> extern bool is_inexpensive_builtin (tree);
> -extern tree compute_objsize (tree, int, tree * = NULL);
> +tree gimple_call_alloc_size (gimple *);
> +extern tree compute_objsize (tree, int, tree * = NULL, tree * = NULL);
>
> extern bool readonly_data_expr (tree exp);
> extern bool init_target_chars (void);
Is there a reason
[PING 2][PATCH] extend -Wstringop-overflow to allocated objects (PR 91582)
Ping: https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00652.html
This change is independent of either of the two patches below:
https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00429.html
https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00652.html
On 11/18/19 11:22 AM, Martin Sebor wrote:
Ping: https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00652.html
On 11/8/19 3:11 PM, Martin Sebor wrote:
Unless it's used with _FORTIFY_SOURCE, -Wstringop-overflow
doesn't consider out-of-bounds accesses to objects allocated
by alloca, malloc, other functions declared with attribute
alloc_size, or even VLAs with variable bounds. This was
a known limitation of the checks (done just before expansion)
relying on the the object size pass when they were introduced
in GCC 7.
But since its introduction in GCC 7, the warning has evolved
beyond some of the limitations of the object size pass. Unlike
it, the warning considers non-constant offsets and stores with
non-constant sizes. Attached is a simple enhancement that
(finally) adds the ability to also detect overflow in allocated
objects to the warning.
With the patch GCC detects the overflow in code like this:
char* f (void)
{
char s[] = "12345";
char *p = malloc (strlen (s));
strcpy (p, s); // warning here
return p;
}
but not (yet) in something like this:
char* g (const char *s)
{
char *p = malloc (strlen (s));
strcpy (p, s); // no warning (yet)
return p;
}
and quite a few other examples. Doing better requires extending
the strlen pass. I'm working on this extension and expect to
submit a patch before stage 1 ends.
Martin
PS I was originally planning to do all the allocation checking
in the strlen pass but it occurred to me that by also enhancing
the compute_objsize function, all warnings that use it will
benefit. Besides -Wstringop-overflow this includes a subset
of -Warray-bounds, -Wformat-overflow, and -Wrestrict. It's
nice when a small enhancement has such a broad positive effect.
[PING][PATCH] extend -Wstringop-overflow to allocated objects (PR 91582)
Ping: https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00652.html
On 11/8/19 3:11 PM, Martin Sebor wrote:
Unless it's used with _FORTIFY_SOURCE, -Wstringop-overflow
doesn't consider out-of-bounds accesses to objects allocated
by alloca, malloc, other functions declared with attribute
alloc_size, or even VLAs with variable bounds. This was
a known limitation of the checks (done just before expansion)
relying on the the object size pass when they were introduced
in GCC 7.
But since its introduction in GCC 7, the warning has evolved
beyond some of the limitations of the object size pass. Unlike
it, the warning considers non-constant offsets and stores with
non-constant sizes. Attached is a simple enhancement that
(finally) adds the ability to also detect overflow in allocated
objects to the warning.
With the patch GCC detects the overflow in code like this:
char* f (void)
{
char s[] = "12345";
char *p = malloc (strlen (s));
strcpy (p, s); // warning here
return p;
}
but not (yet) in something like this:
char* g (const char *s)
{
char *p = malloc (strlen (s));
strcpy (p, s); // no warning (yet)
return p;
}
and quite a few other examples. Doing better requires extending
the strlen pass. I'm working on this extension and expect to
submit a patch before stage 1 ends.
Martin
PS I was originally planning to do all the allocation checking
in the strlen pass but it occurred to me that by also enhancing
the compute_objsize function, all warnings that use it will
benefit. Besides -Wstringop-overflow this includes a subset
of -Warray-bounds, -Wformat-overflow, and -Wrestrict. It's
nice when a small enhancement has such a broad positive effect.
[PATCH] extend -Wstringop-overflow to allocated objects (PR 91582)
Unless it's used with _FORTIFY_SOURCE, -Wstringop-overflow
doesn't consider out-of-bounds accesses to objects allocated
by alloca, malloc, other functions declared with attribute
alloc_size, or even VLAs with variable bounds. This was
a known limitation of the checks (done just before expansion)
relying on the the object size pass when they were introduced
in GCC 7.
But since its introduction in GCC 7, the warning has evolved
beyond some of the limitations of the object size pass. Unlike
it, the warning considers non-constant offsets and stores with
non-constant sizes. Attached is a simple enhancement that
(finally) adds the ability to also detect overflow in allocated
objects to the warning.
With the patch GCC detects the overflow in code like this:
char* f (void)
{
char s[] = "12345";
char *p = malloc (strlen (s));
strcpy (p, s); // warning here
return p;
}
but not (yet) in something like this:
char* g (const char *s)
{
char *p = malloc (strlen (s));
strcpy (p, s); // no warning (yet)
return p;
}
and quite a few other examples. Doing better requires extending
the strlen pass. I'm working on this extension and expect to
submit a patch before stage 1 ends.
Martin
PS I was originally planning to do all the allocation checking
in the strlen pass but it occurred to me that by also enhancing
the compute_objsize function, all warnings that use it will
benefit. Besides -Wstringop-overflow this includes a subset
of -Warray-bounds, -Wformat-overflow, and -Wrestrict. It's
nice when a small enhancement has such a broad positive effect.
PR middle-end/91582 - missing heap overflow detection for strcpy
gcc/ChangeLog:
* builtins.c (gimple_call_alloc_size): New function.
(compute_objsize): Add argument. Call gimple_call_alloc_size.
Handle variable offsets and indices.
* builtins.h (gimple_call_alloc_size): Declare.
(compute_objsize): Add argument.
* tree-ssa-strlen.c (handle_store): Handle calls to allocated objects.
gcc/testsuite/ChangeLog:
* c-c++-common/Wstringop-truncation.c: Remove xfails.
* gcc/testsuite/g++.dg/ext/attr-alloc_size.C: Suppress -Warray-bounds.
* gcc.dg/Wstringop-overflow-22.c: New test.
* gcc/testsuite/gcc.dg/attr-alloc_size.c: Suppress -Warray-bounds.
* gcc/testsuite/gcc.dg/attr-copy-2.c: Same.
* gcc.dg/builtin-stringop-chk-5.c: Remove xfails.
* gcc.dg/builtin-stringop-chk-8.c: Same. Correct the text of expected
warnings.
* gcc.target/i386/pr82002-2a.c: Prune expected warning.
* gcc.target/i386/pr82002-2b.c: Same.
Index: gcc/builtins.c
===
--- gcc/builtins.c (revision 277978)
+++ gcc/builtins.c (working copy)
@@ -3563,6 +3563,80 @@ check_access (tree exp, tree, tree, tree dstwrite,
return true;
}
+/* If STMT is a call to an allocation function, returns the size
+ of the object allocated by the call. */
+
+tree
+gimple_call_alloc_size (gimple *stmt)
+{
+ if (!stmt)
+return NULL_TREE;
+
+ tree allocfntype;
+ if (tree fndecl = gimple_call_fndecl (stmt))
+allocfntype = TREE_TYPE (fndecl);
+ else
+allocfntype = gimple_call_fntype (stmt);
+
+ if (!allocfntype)
+return NULL_TREE;
+
+ unsigned argidx1 = UINT_MAX, argidx2 = UINT_MAX;
+ tree at = lookup_attribute ("alloc_size", TYPE_ATTRIBUTES (allocfntype));
+ if (!at)
+{
+ if (!gimple_call_builtin_p (stmt, BUILT_IN_ALLOCA_WITH_ALIGN))
+ return NULL_TREE;
+
+ argidx1 = 0;
+}
+
+ unsigned nargs = gimple_call_num_args (stmt);
+
+ if (argidx1 == UINT_MAX)
+{
+ tree atval = TREE_VALUE (at);
+ if (!atval)
+ return NULL_TREE;
+
+ argidx1 = TREE_INT_CST_LOW (TREE_VALUE (atval)) - 1;
+ if (nargs <= argidx1)
+ return NULL_TREE;
+
+ atval = TREE_CHAIN (atval);
+ if (atval)
+ {
+ argidx2 = TREE_INT_CST_LOW (TREE_VALUE (atval)) - 1;
+ if (nargs <= argidx2)
+ return NULL_TREE;
+ }
+}
+
+ tree size = gimple_call_arg (stmt, argidx1);
+ tree n = argidx2 < nargs ? gimple_call_arg (stmt, argidx2) : integer_one_node;
+
+ /* To handle ranges do the math in wide_int and return the product
+ of the upper bounds as a constant. Ignore anti-ranges. */
+ wide_int rng1[2];
+ if (TREE_CODE (size) == INTEGER_CST)
+rng1[0] = rng1[1] = wi::to_wide (size);
+ else if (TREE_CODE (size) != SSA_NAME
+ || get_range_info (size, rng1, rng1 + 1) != VR_RANGE)
+return NULL_TREE;
+
+ wide_int rng2[2];
+ if (TREE_CODE (n) == INTEGER_CST)
+rng2[0] = rng2[1] = wi::to_wide (n);
+ else if (TREE_CODE (n) != SSA_NAME
+ || get_range_info (n, rng2 + 1, rng2 + 1) != VR_RANGE)
+return NULL_TREE;
+
+ const int prec = TYPE_PRECISION (sizetype);
+ rng1[1] = wide_int::from (rng1[1], prec, UNSIGNED);
+ rng2[1] = wide_int::from (rng2[1], prec, UNSIGNED);
+ return wide_int_to_tree (sizetype, rng1[1] * rng2[1]);
+}
+
/* Helper to compute the size of the object referenced by the DEST
expression which must have pointer type, using
