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From: Paul Moore <paul@paul-moore.com>
To: Jan Stancek <jstancek@redhat.com>
Cc: selinux@tycho.nsa.gov, sds@tycho.nsa.gov
Subject: Re: [selinux-testsuite PATCH 3/4] mmap/mprotect_heap: make sure
 memory is allocated from heap
Date: Fri, 06 Nov 2015 13:14:54 -0500
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On Friday, November 06, 2015 02:07:23 PM Jan Stancek wrote:
> This test failed on ppc64 with 64k pagesize because memory
> allocation used mmap() instead of advancing heap.
> 
> Use mallopt(M_MMAP_THRESHOLD,..) with large enough value
> to discourage use of mmap().
> 
> Also set length in mprotect to pagesize, kernel silently aligns
> it to pagesize anyway.
> 
> Signed-off-by: Jan Stancek <jstancek@redhat.com>
> Cc: Paul Moore <paul@paul-moore.com>
> Cc: Stephen Smalley <sds@tycho.nsa.gov>
> ---
>  tests/mmap/mprotect_heap.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/tests/mmap/mprotect_heap.c b/tests/mmap/mprotect_heap.c
> index 691299493c3f..8b4321d6fc0b 100644
> --- a/tests/mmap/mprotect_heap.c
> +++ b/tests/mmap/mprotect_heap.c
> @@ -3,6 +3,7 @@
>  #include <stdlib.h>
>  #include <errno.h>
>  #include <sys/mman.h>
> +#include <malloc.h>
> 
>  int main(void)
>  {
> @@ -10,13 +11,19 @@ int main(void)
>  	int rc;
>  	int pagesize = getpagesize();
> 
> +	rc = mallopt(M_MMAP_THRESHOLD, pagesize * 16);
> +	if (rc != 1) {
> +		fprintf(stderr, "mallopt failed: %d\n", rc);
> +		exit(1);
> +	}

Can you explain how you arrived at 16?  It looks a bit like a magic number to 
me, which always gives me pause.  Based on a quick read of the man page, it 
would seem like any value greater than "pagesize" would work, yes?

>  	rc = posix_memalign(&ptr, pagesize, pagesize);
>  	if (rc) {
>  		fprintf(stderr, "posix_memalign failed: %d\n", rc);
>  		exit(1);
>  	}
> 
> -	rc = mprotect(ptr, 4096, PROT_READ | PROT_EXEC);
> +	rc = mprotect(ptr, pagesize, PROT_READ | PROT_EXEC);
>  	if (rc < 0) {
>  		perror("mprotect");
>  		exit(1);

-- 
paul moore
www.paul-moore.com