Hi Daniel, On Wed, Apr 25, 2018 at 11:12:21AM +0200, Daniel Borkmann wrote: > On 04/25/2018 10:18 AM, Leo Yan wrote: > > After enabled BPF_JIT_ALWAYS_ON config, bpf_jit_enable always equals to > > 1; it is impossible to set 'bpf_jit_enable = 2' and the kernel has no > > chance to call bpf_jit_dump(). > > > > This patch relaxes bpf_jit_enable range to [1..2] when kernel config > > BPF_JIT_ALWAYS_ON is enabled so can invoke jit dump. > > > > Signed-off-by: Leo Yan <leo....@linaro.org> > > Is there a specific reason why you need this here instead of retrieving the > dump from the newer interface available from bpftool (tools/bpf/bpftool/)? > The bpf_jit_enable = 2 is not recommended these days since it dumps into the > kernel log which is often readable from unpriv as well. bpftool makes use > of the BPF_OBJ_GET_INFO_BY_FD interface via bpf syscall to get the JIT dump > instead when bpf_jit_enable is set.
Thanks for reviewing. When I read the doc Documentation/networking/filter.txt and the section "JIT compiler" it suggests as below. So I tried to set 'bpf_jit_enable = 2' to dump JIT code, but it failed. If we have concern for security issue, should we remove support for 'bpf_jit_enable = 2' and modify the doc to reflect this change? ---8<--- For JIT developers, doing audits etc, each compile run can output the generated opcode image into the kernel log via: echo 2 > /proc/sys/net/core/bpf_jit_enable Example output from dmesg: [ 3389.935842] flen=6 proglen=70 pass=3 image=ffffffffa0069c8f [ 3389.935847] JIT code: 00000000: 55 48 89 e5 48 83 ec 60 48 89 5d f8 44 8b 4f 68 [ 3389.935849] JIT code: 00000010: 44 2b 4f 6c 4c 8b 87 d8 00 00 00 be 0c 00 00 00 [ 3389.935850] JIT code: 00000020: e8 1d 94 ff e0 3d 00 08 00 00 75 16 be 17 00 00 [ 3389.935851] JIT code: 00000030: 00 e8 28 94 ff e0 83 f8 01 75 07 b8 ff ff 00 00 [ 3389.935852] JIT code: 00000040: eb 02 31 c0 c9 c3 > > --- > > net/core/sysctl_net_core.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c > > index b1a2c5e..6a39b22 100644 > > --- a/net/core/sysctl_net_core.c > > +++ b/net/core/sysctl_net_core.c > > @@ -371,7 +371,7 @@ static int proc_dointvec_minmax_bpf_enable(struct > > ctl_table *table, int write, > > .proc_handler = proc_dointvec_minmax_bpf_enable, > > # ifdef CONFIG_BPF_JIT_ALWAYS_ON > > .extra1 = &one, > > - .extra2 = &one, > > + .extra2 = &two, > > # else > > .extra1 = &zero, > > .extra2 = &two, > > >
