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From: Alexei Starovoitov <>
To: Andrii Nakryiko <>
Subject: Re: [PATCH bpf-next 0/7] libbpf feature probing and sanitization improvements
Date: Tue, 18 Aug 2020 17:24:27 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Tue, Aug 18, 2020 at 02:33:49PM -0700, Andrii Nakryiko wrote:
> This patch set refactors libbpf feature probing to be done lazily on as-needed
> basis, instead of proactively testing all possible features libbpf knows
> about. This allows to scale such detections and mitigations better, without
> issuing unnecessary syscalls on each bpf_object__load() call. It's also now
> memoized globally, instead of per-bpf_object.
> Building on that, libbpf will now detect availability of
> bpf_probe_read_kernel() helper (which means also -user and -str variants), and
> will sanitize BPF program code by replacing such references to generic
> variants (bpf_probe_read[_str]()). This allows to migrate all BPF programs
> into proper -kernel/-user probing helpers, without the fear of breaking them
> for old kernels.
> With that, update BPF_CORE_READ() and related macros to use
> bpf_probe_read_kernel(), as it doesn't make much sense to do CO-RE relocations
> against user-space types. And the only class of cases in which BPF program
> might read kernel type from user-space are UAPI data structures which by
> definition are fixed in their memory layout and don't need relocating. This is
> exemplified by test_vmlinux test, which is fixed as part of this patch set as
> well. BPF_CORE_READ() is useful for chainingg bpf_probe_read_{kernel,user}()
> calls together even without relocation, so we might add user-space variants,
> if there is a need.
> While at making libbpf more useful for older kernels, also improve handling of
> a complete lack of BTF support in kernel by not even attempting to load BTF
> info into kernel. This eliminates annoying warning about lack of BTF support
> in the kernel and map creation retry without BTF. If user is using features
> that require kernel BTF support, it will still fail, of course.

Applied, Thanks

      parent reply	other threads:[~2020-08-19  0:24 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-18 21:33 Andrii Nakryiko
2020-08-18 21:33 ` [PATCH bpf-next 1/7] libbpf: disable -Wswitch-enum compiler warning Andrii Nakryiko
2020-08-19  1:23   ` Yonghong Song
2020-08-19  1:39     ` Andrii Nakryiko
2020-08-19  5:44       ` Yonghong Song
2020-08-18 21:33 ` [PATCH bpf-next 2/7] libbpf: make kernel feature probing lazy Andrii Nakryiko
2020-08-18 21:33 ` [PATCH bpf-next 3/7] libbpf: factor out common logic of testing and closing FD Andrii Nakryiko
2020-08-18 21:33 ` [PATCH bpf-next 4/7] libbpf: sanitize BPF program code for bpf_probe_read_{kernel,user}[_str] Andrii Nakryiko
2020-08-19  1:42   ` Yonghong Song
2020-08-19 20:11     ` Andrii Nakryiko
2020-08-19 20:15       ` Alexei Starovoitov
2020-08-19 20:23         ` Andrii Nakryiko
2020-08-18 21:33 ` [PATCH bpf-next 5/7] selftests/bpf: fix test_vmlinux test to use bpf_probe_read_user() Andrii Nakryiko
2020-08-18 21:33 ` [PATCH bpf-next 6/7] libbpf: switch tracing and CO-RE helper macros to bpf_probe_read_kernel() Andrii Nakryiko
2020-08-18 21:33 ` [PATCH bpf-next 7/7] libbpf: detect minimal BTF support and skip BTF loading, if missing Andrii Nakryiko
2020-08-19  0:24 ` Alexei Starovoitov [this message]

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