From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Alexei Starovoitov <ast@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>,
Daniel Borkmann <daniel@iogearbox.net>,
x86@kernel.org, Networking <netdev@vger.kernel.org>,
bpf <bpf@vger.kernel.org>, Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v2 bpf-next 09/12] bpf: add support for BTF pointers to x86 JIT
Date: Fri, 11 Oct 2019 11:48:19 -0700 [thread overview]
Message-ID: <CAEf4BzZ3A47KQB1uN0nu2JPdm-a+Kx0fkkkp+JRRLNs4DJJ3hw@mail.gmail.com> (raw)
In-Reply-To: <20191010041503.2526303-10-ast@kernel.org>
On Wed, Oct 9, 2019 at 9:15 PM Alexei Starovoitov <ast@kernel.org> wrote:
>
> Pointer to BTF object is a pointer to kernel object or NULL.
> Such pointers can only be used by BPF_LDX instructions.
> The verifier changed their opcode from LDX|MEM|size
> to LDX|PROBE_MEM|size to make JITing easier.
> The number of entries in extable is the number of BPF_LDX insns
> that access kernel memory via "pointer to BTF type".
> Only these load instructions can fault.
> Since x86 extable is relative it has to be allocated in the same
> memory region as JITed code.
> Allocate it prior to last pass of JITing and let the last pass populate it.
> Pointer to extable in bpf_prog_aux is necessary to make page fault
> handling fast.
> Page fault handling is done in two steps:
> 1. bpf_prog_kallsyms_find() finds BPF program that page faulted.
> It's done by walking rb tree.
> 2. then extable for given bpf program is binary searched.
> This process is similar to how page faulting is done for kernel modules.
> The exception handler skips over faulting x86 instruction and
> initializes destination register with zero. This mimics exact
> behavior of bpf_probe_read (when probe_kernel_read faults dest is zeroed).
>
> JITs for other architectures can add support in similar way.
> Until then they will reject unknown opcode and fallback to interpreter.
>
> Since extable should be aligned and placed near JITed code
> make bpf_jit_binary_alloc() return 4 byte aligned image offset,
> so that extable aligning formula in bpf_int_jit_compile() doesn't need
> to rely on internal implementation of bpf_jit_binary_alloc().
> On x86 gcc defaults to 16-byte alignment for regular kernel functions
> due to better performance. JITed code may be aligned to 16 in the future,
> but it will use 4 in the meantime.
>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---
Acked-by: Andrii Nakryiko <andriin@fb.com>
> arch/x86/net/bpf_jit_comp.c | 97 +++++++++++++++++++++++++++++++++++--
> include/linux/bpf.h | 3 ++
> include/linux/extable.h | 10 ++++
> kernel/bpf/core.c | 20 +++++++-
> kernel/bpf/verifier.c | 1 +
> kernel/extable.c | 2 +
> 6 files changed, 128 insertions(+), 5 deletions(-)
>
[...]
next prev parent reply other threads:[~2019-10-11 18:48 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-10 4:14 [PATCH v2 bpf-next 00/12] bpf: revolutionize bpf tracing Alexei Starovoitov
2019-10-10 4:14 ` [PATCH v2 bpf-next 01/12] bpf: add typecast to raw_tracepoints to help BTF generation Alexei Starovoitov
2019-10-10 4:14 ` [PATCH v2 bpf-next 02/12] bpf: add typecast to bpf helpers " Alexei Starovoitov
2019-10-10 4:14 ` [PATCH v2 bpf-next 03/12] bpf: process in-kernel BTF Alexei Starovoitov
2019-10-11 17:56 ` Andrii Nakryiko
2019-10-10 4:14 ` [PATCH v2 bpf-next 04/12] bpf: add attach_btf_id attribute to program load Alexei Starovoitov
2019-10-11 17:58 ` Andrii Nakryiko
2019-10-10 4:14 ` [PATCH v2 bpf-next 05/12] libbpf: auto-detect btf_id of raw_tracepoint Alexei Starovoitov
2019-10-11 18:02 ` Andrii Nakryiko
2019-10-11 18:07 ` Andrii Nakryiko
2019-10-12 0:40 ` Alexei Starovoitov
2019-10-12 1:29 ` Alexei Starovoitov
2019-10-12 4:38 ` Andrii Nakryiko
2019-10-12 4:53 ` Alexei Starovoitov
2019-10-12 4:39 ` Andrii Nakryiko
2019-10-10 4:14 ` [PATCH v2 bpf-next 06/12] bpf: implement accurate raw_tp context access via BTF Alexei Starovoitov
2019-10-11 18:31 ` Andrii Nakryiko
2019-10-11 23:13 ` Andrii Nakryiko
2019-10-10 4:14 ` [PATCH v2 bpf-next 07/12] bpf: attach raw_tp program with BTF via type name Alexei Starovoitov
2019-10-11 18:44 ` Andrii Nakryiko
2019-10-10 4:14 ` [PATCH v2 bpf-next 08/12] bpf: add support for BTF pointers to interpreter Alexei Starovoitov
2019-10-10 4:15 ` [PATCH v2 bpf-next 09/12] bpf: add support for BTF pointers to x86 JIT Alexei Starovoitov
2019-10-11 18:48 ` Andrii Nakryiko [this message]
2019-10-10 4:15 ` [PATCH v2 bpf-next 10/12] bpf: check types of arguments passed into helpers Alexei Starovoitov
2019-10-11 19:02 ` Andrii Nakryiko
2019-10-12 1:39 ` Alexei Starovoitov
2019-10-12 4:25 ` Andrii Nakryiko
2019-10-10 4:15 ` [PATCH v2 bpf-next 11/12] bpf: disallow bpf_probe_read[_str] helpers Alexei Starovoitov
2019-10-11 19:03 ` Andrii Nakryiko
2019-10-10 4:15 ` [PATCH v2 bpf-next 12/12] selftests/bpf: add kfree_skb raw_tp test Alexei Starovoitov
2019-10-10 11:07 ` Ido Schimmel
2019-10-10 19:07 ` Alexei Starovoitov
2019-10-11 19:05 ` Andrii Nakryiko
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