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SubjectRe: [PATCH v3 3/4] x86, mpx: add prctl commands PR_MPX_INIT, PR_MPX_RELEASE
On 01/26/2014 11:14 PM, Ingo Molnar wrote:
>
> * Ren, Qiaowei <qiaowei.ren@intel.com> wrote:
>
>> The size of one bound table is 4M bytes for 64bit, and 16K bytes for
>> 32bit. It can not be accessed by user-space, and it will be accessed
>> automatically by hardware.
>
> So, here's the bound-table allocation AFAICS:
>
> +static bool allocate_bt(unsigned long bd_entry)
> +{
> + unsigned long bt_size = 1UL << (MPX_L2_BITS+MPX_L2_SHIFT);
> + unsigned long bt_addr, old_val = 0;
> +
> + bt_addr = sys_mmap_pgoff(0, bt_size, PROT_READ | PROT_WRITE,
> + MAP_ANONYMOUS | MAP_PRIVATE | MAP_POPULATE, -1, 0);
>
> What ensures that user-space cannot access (and in particular, modify)
> the pages at bt_addr? It's a read-write anonymous mapping AFAICS.
>
Looks like that we can not be able to ensure this. I just mean that
user-space doesn't know the bound tables, and it should not access them
also.

Thanks,
Qiaowei


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