[x32] PATCH: Remove ix86_promote_function_mode

H. Peter Anvin hpa@zytor.com
Tue Jun 21 01:15:00 GMT 2011


Richard Henderson <rth@redhat.com> wrote:

>On 06/20/2011 04:39 PM, H. Peter Anvin wrote:
>> sys_foo:
>> 	cmpl	$10, %edi
>> 	jae	.L1
>> 
>> 	movq	foo_table(,%rdi,3), %rax
>> 	retq
>> .L1:
>> 	movq	$-EINVAL, %rax
>> 	retq
>> 
>> Enter this function with a non-normalized %rdi and you have a
>security
>> hole even though the C is perfectly fine.
>
>Yes, I get that.  Isn't it already the case that x86_64 defines the
>upper half of 32-bit inputs as garbage?  Assuming you're never
>intending
>to run an x32 kernel, but always an x32 environment within an x86_64
>kernel, where does the talk of security holes wrt non-pointers come
>from?
>
>
>r~

H.J. was proposing an ABI change.  I wanted to explain that the current ABI is the way it is for a reason.  x32 pointers, however, can and should be zero-extended since they will be 64 bits in the kernel, as you correctly point out.
-- 
Sent from my mobile phone. Please excuse my brevity and lack of formatting.



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