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SubjectRe: Understanding Linux addr space, malloc, and heap
Arjan van de Ven wrote:
> On Fri, 2005-10-21 at 09:45 -0400, Vincent W. Freeh wrote:
>
>>Thanks for your quick response. It basically confirmed that I observed
>>what I thought I did. However, I am no closer to solving my problem. I
>>cannot mprotect data that I malloc beyond the first 65 pages.
>
>
> you can't mprotect malloc() memory period ..

Actually, I can and do. Simple program at end.

>
>> Why is
>>that? Can that be fixed? Second, why does mprotect silently fail? I
>>could live with it failing--but I cannot deal with a call the "works"
>>but doesn't work.
>
>
> need more info :)
>

I call mprotect and it return 0--meaning it succeeded. But the
permissions on the page remain rw. So it fails to change the
permissions, but doesn't give any indication of this.

Thanks,
vince.

------------------
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
void *p;
int pgsize = getpagesize();

p = malloc(1024);
mprotect((void*)((unsigned)p & ~(pgsize-1)), 1024, PROT_NONE);
printf("\t*p = %d\n", *(int *)p);
return 0;
}
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