mprotect(PROT_NONE) doesn't prevent reading/writing on 2.6.14 Au1550

mprotect(PROT_NONE) doesn't prevent reading/writing on 2.6.14 Au1550

[Clem Taylor]

[-- Attachment #1: Type: text/plain, Size: 669 bytes --]

Hi,

It seems that mprotect(PROT_NONE) isn't actually doing anything on my
2.6.14 au1550 system.

Attached is a simple test that allocates 64K (64K aligned),
reads/writes the buffer, mprotect(PROT_NONE) the buffer and then
attempts to read and write to the buffer a second time. I expected
that writing to a PROT_NONE page would result in a segfault, but on
the Au1550 the program runs without faulting. Running the same code on
x86 (2.6.13) segfaults as expected.

Is there some reason why mprotect() wouldn't work on the Au1550, or is
this a bug?

                                         Thanks,
                                         Clem Taylor

[-- Attachment #2: mprotectTest.c --]
[-- Type: text/x-csrc, Size: 1124 bytes --]

#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;

    /* allocate 64K, 64K aligned */
    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 buffer, should segfault */
    memset ( buffer, 0x55, size );

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

    return 0;
}

Re: mprotect(PROT_NONE) doesn't prevent reading/writing on 2.6.14 Au1550

[Pete Popov]

On Mon, 2005-12-12 at 16:34 -0500, Clem Taylor wrote:
> Hi,
> 
> It seems that mprotect(PROT_NONE) isn't actually doing anything on my
> 2.6.14 au1550 system.
> 
> Attached is a simple test that allocates 64K (64K aligned),
> reads/writes the buffer, mprotect(PROT_NONE) the buffer and then
> attempts to read and write to the buffer a second time. I expected
> that writing to a PROT_NONE page would result in a segfault, but on
> the Au1550 the program runs without faulting. Running the same code on
> x86 (2.6.13) segfaults as expected.
> 
> Is there some reason why mprotect() wouldn't work on the Au1550, or is
> this a bug?

Do you have another MIPS system you can test this on?

Pete