Re: [Xen-devel] [PATCH v6.5 08/26] x86/entry: Erase guest GPR state on entry to Xen

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 22/01/2018 10:04, David Woodhouse wrote:
> On Thu, 2018-01-04 at 00:15 +0000, Andrew Cooper wrote:
>> --- a/xen/include/asm-x86/asm_defns.h
>> +++ b/xen/include/asm-x86/asm_defns.h
>> @@ -217,22 +217,34 @@ static always_inline void stac(void)
>>          addq  $-(UREGS_error_code-UREGS_r15), %rsp
>>          cld
>>          movq  %rdi,UREGS_rdi(%rsp)
>> +        xor   %edi, %edi
>>          movq  %rsi,UREGS_rsi(%rsp)
>> +        xor   %esi, %esi
>>          movq  %rdx,UREGS_rdx(%rsp)
>> +        xor   %edx, %edx
>>          movq  %rcx,UREGS_rcx(%rsp)
>> +        xor   %ecx, %ecx
>>          movq  %rax,UREGS_rax(%rsp)
>> +        xor   %eax, %eax
> You didn't want to erase all 64 bits?

This does erase all 64 bits.  (We're in long mode, so the upper 32 bits
are implicitly zeroed, without an added rex prefix.)

~Andrew

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