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.
