Re: bpf: undefined shift in __bpf_prog_run

[Alexei Starovoitov]

On Fri, Dec 04, 2015 at 08:48:57PM +0100, Dmitry Vyukov wrote:
> 
> For example, a compiler can assume that result of left shift is larger
> or equal to first operand, which in turn can allow it to elide some
> bounds check in code, which in turn can lead to an exploit. I am not
> saying that this particular pattern is present in the code, what I
> want to say is that such undefined behaviors can lead to very
> unpredictable and unexpected consequences.

Within bpf it cannot.
shift is not used in any memory or bounds operations.
so reg <<= 1234 cannot be exploited.

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