[x32] PATCH: Remove ix86_promote_function_mode

Richard Henderson rth@redhat.com
Mon Jun 20 22:58:00 GMT 2011


On 06/20/2011 07:33 AM, H. Peter Anvin wrote:
> On 06/20/2011 07:01 AM, H.J. Lu wrote:
>> On Mon, Jun 20, 2011 at 6:53 AM, Bernd Schmidt <bernds@codesourcery.com> wrote:
>>> On 06/20/2011 03:51 PM, H.J. Lu wrote:
>>>> Promote pointers to Pmode when passing/returning in registers is
>>>> a security concern.
> 
> No.  Promoting *NON*-pointers (or rather, requiring non-pointers to
> having already been zero extended) is a security concern.  I thought I'd
> made that point clear already.  This is a hideously critical distinction.
> 
>> Peter, do you think it is safe to assume upper 32bits are zero in
>> user space for x32? Kernel isn't a problem since pointer is 64bit
>> in kernel and we don't pass pointers on stack to kernel.
> 
> As I have already stated, if we *cannot* require pointers to be
> zero-extended on entry to the kernel, we're going to have to have
> special entry points for all the x32 system calls except the ones that
> don't take pointers.

If it's a security concern, surely you have to do it in the kernel
anyway, lest someone call into the kernel via their own assembly
rather than something controlled by the compiler...


r~



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