So You Think You Can Const?

Hi everybody,
I am back to programming in C after many years:
indeed I have forgotten so many things, including
how much I love this language. :)
In particular, I am using C90, and compiling with
`gcc ... -ansi -pedantic -Wall -Wextra` (as I have
the requirement to ideally support any device).
To the question, I was reading this, but I am not
sure what the quoted passage means:
Matt Stancliff, "So You Think You Can Const?",
<https://matt.sh/sytycc>
<< Your compiler, at its discretion, may also choose
    to place any const declarations in read-only storage,
    so if you attempt to hack around the const blocks,
    you could get undefined behavior. >>
I do not understand if just declaring that a pointer
is to constant data may incur in that problem even
if the pointed data was in fact allocated with malloc.
I would say of course not, but I am not sure.
E.g. consider this little internal helper of mine
(which implements an interface that is public to
do an internal thing...), where I am casting to
pointer to non-constant data in order to free the
pointed data (i.e. without warning):
```c
static int MyStruct_free_(MyStruct_t const *pT) {
     assert(pT);
     free((MyStruct_t *)pT);
     return 0;
}
```
Assuming, as said, that the data was originally
allocated with malloc, is that code safe or
something can go wrong even in that case?
Thank in advance for any help/insight,
Julio