[x32] PATCH: Remove ix86_promote_function_mode

H. Peter Anvin hpa@zytor.com
Mon Jun 20 14:41:00 GMT 2011


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.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.



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