On Fri, 2005-10-21 at 11:11 -0400, Vincent W. Freeh wrote:-
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.
Ok I meant in the "while adhering to the standard" :)
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.
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#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;
}
this has a bug, the 1024 is wrong... what if your "p" point actually
spans 2 pages?
but to have "some effect" even for malloc-falling-back-to-mmap..
just there's a bunch of collateral damage since you mprotect more than
just the memory you got from malloc. mprotect works on page size.. so if
p spans 2 pages (why wouldn't it ;) you mprotect either the wrong memory
(as in your example) or too much (eg both pages)...