Hi Glider, thank you for the quick answer.
I've some doubt, correct me if I'm wrong.
> No, right now it's not possible. ASan instrumentation doesn't distinguish
between a read and a write.
if ((addr >> 3) + offset) __asan_report_load8(addr);
This is inserted before loads, a quick implementations would be a simple
void __asan_report_load8(uptr add) {
if (((addr >> 3) + offset == ASAN_USER_RDONLY_SHADOW) return;
// .. old __asan_report_load
}
And the same for all other variants like __asan_load8 , __asan_report_loadN
etc...
> If you need a one-off solution for marking some small amount of data
read-only, you can allocate a page-aligned memory chunk with mmap(),
store your data in it and seal it with mprotect().
The libdislocator approach doesn't work if a want a single byte read only
inside a RW region
Il giorno giovedì 12 dicembre 2019 13:08:19 UTC+1, Glider ha scritto:
>
> On Thu, Dec 12, 2019 at 1:03 PM Andrea Fioraldi
> <[email protected] <javascript:>> wrote:
> >
> > Hi to all,
>
> Hi Andrea,
>
> > there is a way to poison bytes as read-only in the ASAN runtime?
> > For instance, I have a type field in a dynamic allocated structure that
> is assigned only at creation
> > and I want to mark it as read-only after the first assignment to detect
> type-confusions.
> > I found nothing searching about it in compiler-rt and so this is more a
> feature request, but maybe I missed it and already exists.
>
> No, right now it's not possible. ASan instrumentation doesn't
> distinguish between a read and a write.
> This can be done on LLVM side, but additional complication doesn't
> sound necessary, especially given that there won't be any automated
> way to mark data read-only.
> Without that this feature will have limited use.
>
> If you need a one-off solution for marking some small amount of data
> read-only, you can allocate a page-aligned memory chunk with mmap(),
> store your data in it and seal it with mprotect().
>
> HTH,
> Alex
>
> >
> > Something like the following snippet would be useful:
> >
> > enum {
> > IS_INT,
> > IS_FLOAT
> > };
> > struct foo {
> > int type;
> > union { int i; float f };
> > };
> >
> > struct foo* create_int_foo(int i) {
> > struct foo * f = malloc(sizeof(struct foo));
> > f->i = i;
> > f->type = IS_INT;
> > ASAN_POISON_RDONLY_MEMORY_REGION(&f->type, sizeof(int));
> > }
> >
> > Thank you!
> >
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>
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