netdev - [PATCH v2 bpf-next 0/4] bpf: Improve verifier test coverage on sparc64 et al.

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Date:   Fri, 30 Nov 2018 21:07:54 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     daniel@...earbox.net
CC:     ast@...nel.org, netdev@...r.kernel.org
Subject: [PATCH v2 bpf-next 0/4] bpf: Improve verifier test coverage on
 sparc64 et al.

On sparc64 a ton of test cases in test_verifier.c fail because
the memory accesses in the test case are unaligned (or cannot
be proven to be aligned by the verifier).

Perhaps we can eventually try to (carefully) modify each test case
which has this problem to not use unaligned accesses but:

1) That is delicate work.

2) The changes might not fully respect the original
   intention of the testcase.

3) In some cases, such a transformation might not even
   be feasible at all.

So add an "any alignment" flag to tell the verifier to forcefully
disable it's alignment checks completely.

test_verifier.c is then annotated to use this flag when necessary.

The presence of the flag in each test case is good documentation to
anyone who wants to actually tackle the job of eliminating the
unaligned memory accesses in the test cases.

I've also seen several weird things in test cases, like trying to
access __skb->mark in a packet buffer.

This gets rid of 104 test_verifier.c failures on sparc64.

Changes since v1:

1) Explain the new BPF_PROG_LOAD flag in easier to understand terms.
   Suggested by Alexei.

2) Make bpf_verify_program() just take a __u32 prog_flags instead of
   just accumulating boolean arguments over and over.  Also suggested
   by Alexei.

Changes since RFC:

1) Only the admin can allow the relaxation of alignment restrictions
   on inefficient unaligned access architectures.

2) Use F_NEEDS_EFFICIENT_UNALIGNED_ACCESS instead of making a new
   flag.

3) Annotate in the output, when we have a test case that the verifier
   accepted but we did not try to execute because we are on an
   inefficient unaligned access platform.  Maybe with some arch
   machinery we can avoid this in the future.

Signed-off-by: David S. Miller <davem@...emloft.net>