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Message-ID: <cf475fe0-9961-d768-fae3-04f640855dab@iogearbox.net>
Date: Tue, 3 Jan 2023 16:41:58 +0100
From: Daniel Borkmann <daniel@...earbox.net>
To: xxmy@...ragraf.org, bpf@...r.kernel.org, netdev@...r.kernel.org,
linux-arm-kernel@...ts.infradead.or, loongarch@...ts.linux.dev,
linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
sparclinux@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>,
Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
Hou Tao <houtao1@...wei.com>
Subject: Re: [bpf-next v1] bpf: drop deprecated bpf_jit_enable == 2
On 1/3/23 2:24 PM, xxmy@...ragraf.org wrote:
> From: Tonghao Zhang <xxmy@...ragraf.org>
>
> The x86_64 can't dump the valid insn in this way. A test BPF prog
> which include subprog:
>
> $ llvm-objdump -d subprog.o
> Disassembly of section .text:
> 0000000000000000 <subprog>:
> 0: 18 01 00 00 73 75 62 70 00 00 00 00 72 6f 67 00 r1 = 29114459903653235 ll
> 2: 7b 1a f8 ff 00 00 00 00 *(u64 *)(r10 - 8) = r1
> 3: bf a1 00 00 00 00 00 00 r1 = r10
> 4: 07 01 00 00 f8 ff ff ff r1 += -8
> 5: b7 02 00 00 08 00 00 00 r2 = 8
> 6: 85 00 00 00 06 00 00 00 call 6
> 7: 95 00 00 00 00 00 00 00 exit
> Disassembly of section raw_tp/sys_enter:
> 0000000000000000 <entry>:
> 0: 85 10 00 00 ff ff ff ff call -1
> 1: b7 00 00 00 00 00 00 00 r0 = 0
> 2: 95 00 00 00 00 00 00 00 exit
>
> kernel print message:
> [ 580.775387] flen=8 proglen=51 pass=3 image=ffffffffa000c20c from=kprobe-load pid=1643
> [ 580.777236] JIT code: 00000000: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
> [ 580.779037] JIT code: 00000010: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
> [ 580.780767] JIT code: 00000020: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
> [ 580.782568] JIT code: 00000030: cc cc cc
>
> $ bpf_jit_disasm
> 51 bytes emitted from JIT compiler (pass:3, flen:8)
> ffffffffa000c20c + <x>:
> 0: int3
> 1: int3
> 2: int3
> 3: int3
> 4: int3
> 5: int3
> ...
>
> Until bpf_jit_binary_pack_finalize is invoked, we copy rw_header to header
> and then image/insn is valid. BTW, we can use the "bpftool prog dump" JITed instructions.
>
> * clean up the doc
> * remove bpf_jit_disasm tool
> * set bpf_jit_enable only 0 or 1.
>
> Signed-off-by: Tonghao Zhang <xxmy@...ragraf.org>
> Suggested-by: Alexei Starovoitov <ast@...nel.org>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Andrii Nakryiko <andrii@...nel.org>
> Cc: Martin KaFai Lau <martin.lau@...ux.dev>
> Cc: Song Liu <song@...nel.org>
> Cc: Yonghong Song <yhs@...com>
> Cc: John Fastabend <john.fastabend@...il.com>
> Cc: KP Singh <kpsingh@...nel.org>
> Cc: Stanislav Fomichev <sdf@...gle.com>
> Cc: Hao Luo <haoluo@...gle.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Hou Tao <houtao1@...wei.com>
> ---
> Documentation/admin-guide/sysctl/net.rst | 2 +-
> Documentation/networking/filter.rst | 98 +------
> arch/arm/net/bpf_jit_32.c | 4 -
> arch/arm64/net/bpf_jit_comp.c | 4 -
> arch/loongarch/net/bpf_jit.c | 4 -
> arch/mips/net/bpf_jit_comp.c | 3 -
> arch/powerpc/net/bpf_jit_comp.c | 11 -
> arch/riscv/net/bpf_jit_core.c | 3 -
> arch/s390/net/bpf_jit_comp.c | 4 -
> arch/sparc/net/bpf_jit_comp_32.c | 3 -
> arch/sparc/net/bpf_jit_comp_64.c | 13 -
> arch/x86/net/bpf_jit_comp.c | 3 -
> arch/x86/net/bpf_jit_comp32.c | 3 -
> net/core/sysctl_net_core.c | 14 +-
> tools/bpf/.gitignore | 1 -
> tools/bpf/Makefile | 10 +-
> tools/bpf/bpf_jit_disasm.c | 332 -----------------------
> 17 files changed, 8 insertions(+), 504 deletions(-)
> delete mode 100644 tools/bpf/bpf_jit_disasm.c
>
> diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
> index 6394f5dc2303..45d3d965276c 100644
> --- a/Documentation/admin-guide/sysctl/net.rst
> +++ b/Documentation/admin-guide/sysctl/net.rst
> @@ -87,7 +87,7 @@ Values:
>
> - 0 - disable the JIT (default value)
> - 1 - enable the JIT
> - - 2 - enable the JIT and ask the compiler to emit traces on kernel log.
> + - 2 - deprecated in linux 6.2
I'd make it more clear in the docs and reword it as follows (also, it'll be in 6.3, not 6.2):
- 2 - enable the JIT and ask the compiler to emit traces on kernel log.
(deprecated since v6.3, use ``bpftool prog dump jited id <id>`` instead)
>
> bpf_jit_harden
> --------------
[...]
> diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
> index 5b1ce656baa1..731a2eb0f68e 100644
> --- a/net/core/sysctl_net_core.c
> +++ b/net/core/sysctl_net_core.c
> @@ -275,16 +275,8 @@ static int proc_dointvec_minmax_bpf_enable(struct ctl_table *table, int write,
>
> tmp.data = &jit_enable;
> ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
> - if (write && !ret) {
> - if (jit_enable < 2 ||
> - (jit_enable == 2 && bpf_dump_raw_ok(current_cred()))) {
> - *(int *)table->data = jit_enable;
> - if (jit_enable == 2)
> - pr_warn("bpf_jit_enable = 2 was set! NEVER use this in production, only for JIT debugging!\n");
> - } else {
> - ret = -EPERM;
> - }
> - }
> + if (write && !ret)
> + *(int *)table->data = jit_enable;
>
> if (write && ret && min == max)
> pr_info_once("CONFIG_BPF_JIT_ALWAYS_ON is enabled, bpf_jit_enable is permanently set to 1.\n");
> @@ -395,7 +387,7 @@ static struct ctl_table net_core_table[] = {
> .extra2 = SYSCTL_ONE,
> # else
> .extra1 = SYSCTL_ZERO,
> - .extra2 = SYSCTL_TWO,
> + .extra2 = SYSCTL_ONE,
I'd leave it at SYSCTL_TWO to avoid breakage, just that the semantics of 2 will be the same
as 1 going forward.
> # endif
> },
> # ifdef CONFIG_HAVE_EBPF_JIT
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