Re: Do the x86 kernel entry points need an xabort on TSX cpus?

["H. Peter Anvin" <hpa@linux.intel.com>]

On 02/09/2012 11:40 PM, Andy Lutomirski wrote:
> [...]
>
>   - Ring transitions: SYSENTER, SYSCALL, SYSEXIT, and SYSRET.
>
> I suspect that many bits of the kernel expect that things they do
> won't unhappen.  For example, it could be fun to do:
>

That's why entering the kernel will cause an abort.  In other words, you 
will ALWAYS abort when you do a read(), and you will never reach your 
_xabort().

> int devrandom = open("/dev/random", O_RDONLY);
> unsigned int abort_code = _xbegin();
>
> if (abort_code&  1) {
>    printf("Your next random byte is %d\n", (int)(abort_code>>  24));
> } else if (abort_code != 0) {
>    printf("Attack failed\n");
> } else {
>    char r;
>    read(devrandom,&r, 1);
>    _xabort(r);
> }

	-hpa