can read/write to mprotect(PROT_NONE) region with 2.6.14 on au1550

[Clem Taylor <clem.taylor@xxxxxxxxx>]

Hi,

I was trying to use mprotect(PROT_NONE) to help debug a problem, and
it seems that mprotect() isn't actually doing anything with my 2.6.14
linux-mips kernel on an au1550. Attached is a simple test program that
segfaults as expected on x86 (2.6.12), but does not segfault on mips
(2.6.14). I can both read and write PROT_NONE memory without problem,
which should result in a segfault. Originally, I was trying to
mprotect() a mmaped GFP_DMA region which wasn't working and then I
tried a simpler test that also wasn't working.

Shouldn't mprotect() work? Could I be missing a config option, or is
this just broken?

                               Thanks,
                               Clem Taylor

#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <sys/mman.h>
#include <string.h>
#include <errno.h>

int main ( int argc, char *argv [ ] )
{
    int size = 65536, i, ret;
    unsigned char *buffer;

    buffer = memalign ( size, size );
    if ( buffer == NULL )
    {
        fprintf ( stderr, "memalign() failed.\n" );
        return 1;
    }

    fprintf ( stderr, "buffer=%p size=%d\n", buffer, size );

    /* write and read buffer */
    memset ( buffer, 0xAA, size );
    for ( i = 0; i < 2; i++ )
        fprintf ( stderr, "buffer [ %d ] = 0x%02X\n", i, buffer [ i ] );

    /* disable reading and writing */
    ret = mprotect ( buffer, size, PROT_NONE );
    if ( ret != 0 )
    {
        fprintf ( stderr, "mprotect(%p,%d,PROT_NONE) failed: %s\n",
            buffer, size, strerror ( errno ) );
        return 1;
    }

    /* write and read buffer, should segfault */
    memset ( buffer, 0x55, size );
    for ( i = 0; i < 2; i++ )
        fprintf ( stderr, "buffer [ %d ] = 0x%02X\n", i, buffer [ i ] );

    return 0;
}