[PATCH bpf-next 0/4] reduce BPF_ID_MAP_SIZE to fit only valid programs

[Eduard Zingerman <eddyz87@gmail.com>]

This is a follow-up for threads [1] and [2]:
 - The size of the bpf_verifier_state->idmap_scratch array is reduced but
   remains sufficient for any valid BPF program.
 - selftests/bpf test_loader is updated to allow specifying that program
   requires BPF_F_TEST_STATE_FREQ flag.
 - Test case for the verifier.c:check_ids() update uses test_loader and is
   meant as an example of using it for test_verifier-kind tests.

The combination of test_loader and naked functions (see [3]) with inline
assembly allows to write verifier tests easier than it is done currently
with BPF_RAW_INSN-series macros.

One can follow the steps below to add new tests of such kind:
 - add a topic file under bpf/progs/ directory;
 - define test programs using naked functions and inline assembly:

	#include <linux/bpf.h>
	#include "bpf_misc.h"
	
	SEC(...)
	__naked int foo_test(void)
	{
		asm volatile(
			"r0 = 0;"
			"exit;"
			::: __clobber_all);
	}
	
 - add skeleton and runner functions in prog_tests/verifier.c:
 
	#include "topic.skel.h"
	TEST_SET(topic)

After these steps the test_progs binary would include the topic tests.
Topic tests could be selectively executed using the following command:

$ ./test_progs -vvv -a topic

These changes are suggested by Andrii Nakryiko.

[1] https://lore.kernel.org/bpf/CAEf4BzYN1JmY9t03pnCHc4actob80wkBz2vk90ihJCBzi8CT9w@mail.gmail.com/
[2] https://lore.kernel.org/bpf/CAEf4BzYPsDWdRgx+ND1wiKAB62P=WwoLhr2uWkbVpQfbHqi1oA@mail.gmail.com/
[3] https://gcc.gnu.org/onlinedocs/gcc/Basic-Asm.html#Basic-Asm

Eduard Zingerman (4):
  selftests/bpf: support for BPF_F_TEST_STATE_FREQ in test_loader
  selftests/bpf: convenience macro for use with 'asm volatile' blocks
  bpf: reduce BPF_ID_MAP_SIZE to fit only valid programs
  selftests/bpf: check if verifier.c:check_ids() handles 64+5 ids

 include/linux/bpf_verifier.h                  |  4 +-
 kernel/bpf/verifier.c                         |  6 +-
 .../selftests/bpf/prog_tests/verifier.c       | 12 +++
 tools/testing/selftests/bpf/progs/bpf_misc.h  |  7 ++
 .../selftests/bpf/progs/check_ids_limits.c    | 77 +++++++++++++++++++
 tools/testing/selftests/bpf/test_loader.c     | 10 +++
 6 files changed, 112 insertions(+), 4 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/verifier.c
 create mode 100644 tools/testing/selftests/bpf/progs/check_ids_limits.c

-- 
2.38.2