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Re: [x32] PATCH: Remove ix86_promote_function_mode
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.
--
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