On Fri, Mar 3, 2023 at 1:24 PM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
>
> On Fri, 2023-03-03 at 12:28 -0800, Alexei Starovoitov wrote:
> > On Fri, Mar 03, 2023 at 12:55:07AM +0200, Eduard Zingerman wrote:
> > > Function verifier.c:convert_ctx_access() applies some rewrites to BPF
> > > instructions that read or write BPF program context. This commit adds
> > > machinery to allow test cases that inspect BPF program after these
> > > rewrites are applied.
> > >
> > > An example of a test case:
> > >
> > > {
> > > // Shorthand for field offset and size specification
> > > N(CGROUP_SOCKOPT, struct bpf_sockopt, retval),
> > >
> > > // Pattern generated for field read
> > > .read = "$dst = *(u64 *)($ctx + bpf_sockopt_kern::current_task);"
> > > "$dst = *(u64 *)($dst + task_struct::bpf_ctx);"
> > > "$dst = *(u32 *)($dst + bpf_cg_run_ctx::retval);",
> > >
> > > // Pattern generated for field write
> > > .write = "*(u64 *)($ctx + bpf_sockopt_kern::tmp_reg) = r9;"
> > > "r9 = *(u64 *)($ctx + bpf_sockopt_kern::current_task);"
> > > "r9 = *(u64 *)(r9 + task_struct::bpf_ctx);"
> > > "*(u32 *)(r9 + bpf_cg_run_ctx::retval) = $src;"
> > > "r9 = *(u64 *)($ctx + bpf_sockopt_kern::tmp_reg);" ,
> > > },
> > >
> > > For each test case, up to three programs are created:
> > > - One that uses BPF_LDX_MEM to read the context field.
> > > - One that uses BPF_STX_MEM to write to the context field.
> > > - One that uses BPF_ST_MEM to write to the context field.
> > >
> > > The disassembly of each program is compared with the pattern specified
> > > in the test case.
> > >
> > > Kernel code for disassembly is reused (as is in the bpftool).
> > > To keep Makefile changes to the minimum, symbolic links to
> > > `kernel/bpf/disasm.c` and `kernel/bpf/disasm.h ` are added.
> > ...
> > > +static regex_t *compile_regex(char *pat)
> > > +{
> > > + regex_t *re;
> > > + int err;
> > > +
> > > + re = malloc(sizeof(regex_t));
> > > + if (!re) {
> > > + PRINT_FAIL("Can't alloc regex\n");
> > > + return NULL;
> > > + }
> > > +
> > > + err = regcomp(re, pat, REG_EXTENDED);
> >
> > Fancy.
>
> In a good or in a bad way?
> It is the shortest form I came up with...
>
> > What is the cost of running this in test_progs?
> > How many seconds does it add to run time?
>
> About 0.13sec (including modprobe and process initialization):
>
> # time ./test_progs -a "ctx_rewrite/*"
> #58/1 ctx_rewrite/SCHED_CLS.tstamp:OK
> ...
> #58/20 ctx_rewrite/CGROUP_SOCKOPT.optval_end:OK
> #58 ctx_rewrite:OK
> Summary: 1/20 PASSED, 0 SKIPPED, 0 FAILED
>
> real 0m0.131s
> user 0m0.027s
> sys 0m0.046s
>
> It loads 52 programs.
That's fine then. I was worried that compiling regex in a loop
might be slow.
