netdev - more on FP operations

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Date:   Thu, 20 Apr 2017 14:06:17 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     ast@...com
CC:     borkmann@...earbox.net, netdev@...r.kernel.org
Subject: more on FP operations

I'm running test_verifier for testing, and I notice in my JIT that a
32-bit move from the frame pointer (BPF_REG_10) ends up in the JIT.

It is from this test:

		"unpriv: partial copy of pointer",
		.insns = {
			BPF_MOV32_REG(BPF_REG_1, BPF_REG_10),
			BPF_MOV64_IMM(BPF_REG_0, 0),
			BPF_EXIT_INSN(),
		},
		.errstr_unpriv = "R10 partial copy",
		.result_unpriv = REJECT,
		.result = ACCEPT,

It seems to suggest that privileged code is allowed to do this, but I
can't think of a legitimate usage.

I really want to be able to JIT anything the verifier accepts, but I
have a hard time justifying adding 32-bit FP register move support,
adjusting for the stack bias, etc.

Thanks.