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Re: [Xen-devel] Side channel attack


Please don't post HTML mails.

On Fri, Apr 15, 2016 at 03:49:20PM +0800, Zakirasafi wrote:
> Dear All
> The following code is for side channel attack on xen hypevisor. In this
> code I am having problem in understanding the highlighted red line. In the
> line what ".byte 15, byte 49" do???

I don't have HTML capable mail reader, so I can't see "highlighted red
line", but I get you idea.

> #include <sys/types.h>
> #include <sys/socket.h>
> #include <netinet/in.h>
>  #include <openssl/aes.h>
> unsigned int timestamp(void)
>  {
> unsigned int bottom;
> unsigned int top;
> *asm volatile(".byte 15;.byte 49" : "=a"(bottom),"=d"(top)); return bottom;*
>  }

This is probably some sort of opcode. You can probably find out what
they mean in Intel or AMD software developer manual.

Other than that, I don't think we can help you much regarding this
program. You will have better luck contacting the researchers (?) who
wrote this code.

And, if you do find it a security issue in real life, we have a process
of dealing with that, too.



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