linux_dsm_epyc7002/kernel/bpf
Alexei Starovoitov f7cf25b202 bpf: track spill/fill of constants
Compilers often spill induction variables into the stack,
hence it is necessary for the verifier to track scalar values
of the registers through stack slots.

Also few bpf programs were incorrectly rejected in the past,
since the verifier was not able to track such constants while
they were used to compute offsets into packet headers.

Tracking constants through the stack significantly decreases
the chances of state pruning, since two different constants
are considered to be different by state equivalency.
End result that cilium tests suffer serious degradation in the number
of states processed and corresponding verification time increase.

                     before  after
bpf_lb-DLB_L3.o      1838    6441
bpf_lb-DLB_L4.o      3218    5908
bpf_lb-DUNKNOWN.o    1064    1064
bpf_lxc-DDROP_ALL.o  26935   93790
bpf_lxc-DUNKNOWN.o   34439   123886
bpf_netdev.o         9721    31413
bpf_overlay.o        6184    18561
bpf_lxc_jit.o        39389   359445

After further debugging turned out that cillium progs are
getting hurt by clang due to the same constant tracking issue.
Newer clang generates better code by spilling less to the stack.
Instead it keeps more constants in the registers which
hurts state pruning since the verifier already tracks constants
in the registers:
                  old clang  new clang
                         (no spill/fill tracking introduced by this patch)
bpf_lb-DLB_L3.o      1838    1923
bpf_lb-DLB_L4.o      3218    3077
bpf_lb-DUNKNOWN.o    1064    1062
bpf_lxc-DDROP_ALL.o  26935   166729
bpf_lxc-DUNKNOWN.o   34439   174607
bpf_netdev.o         9721    8407
bpf_overlay.o        6184    5420
bpf_lcx_jit.o        39389   39389

The final table is depressing:
                  old clang  old clang    new clang  new clang
                           const spill/fill        const spill/fill
bpf_lb-DLB_L3.o      1838    6441          1923      8128
bpf_lb-DLB_L4.o      3218    5908          3077      6707
bpf_lb-DUNKNOWN.o    1064    1064          1062      1062
bpf_lxc-DDROP_ALL.o  26935   93790         166729    380712
bpf_lxc-DUNKNOWN.o   34439   123886        174607    440652
bpf_netdev.o         9721    31413         8407      31904
bpf_overlay.o        6184    18561         5420      23569
bpf_lxc_jit.o        39389   359445        39389     359445

Tracking constants in the registers hurts state pruning already.
Adding tracking of constants through stack hurts pruning even more.
The later patch address this general constant tracking issue
with coarse/precise logic.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2019-06-19 02:22:51 +02:00
..
arraymap.c bpf: move memory size checks to bpf_map_charge_init() 2019-05-31 16:52:56 -07:00
bpf_lru_list.c bpf: lru: Lower the PERCPU_NR_SCANS from 16 to 4 2017-04-17 13:55:52 -04:00
bpf_lru_list.h bpf: Only set node->ref = 1 if it has not been set 2017-09-01 09:57:39 -07:00
btf.c bpf: allow for key-less BTF in array map 2019-04-09 17:05:46 -07:00
cgroup.c bpf: Update __cgroup_bpf_run_filter_skb with cn 2019-05-31 16:41:29 -07:00
core.c bpf: remove __rcu annotations from bpf_prog_array 2019-05-29 15:17:35 +02:00
cpumap.c bpf: move memory size checks to bpf_map_charge_init() 2019-05-31 16:52:56 -07:00
devmap.c bpf: remove redundant assignment to err 2019-06-04 16:57:07 +02:00
disasm.c bpf: implement lookup-free direct value access for maps 2019-04-09 17:05:46 -07:00
disasm.h bpf: Remove struct bpf_verifier_env argument from print_bpf_insn 2018-03-23 17:38:57 +01:00
hashtab.c bpf: move memory size checks to bpf_map_charge_init() 2019-05-31 16:52:56 -07:00
helpers.c bpf: Introduce bpf_strtol and bpf_strtoul helpers 2019-04-12 13:54:59 -07:00
inode.c bpf: relax inode permission check for retrieving bpf program 2019-05-16 11:31:49 -07:00
local_storage.c bpf: move memory size checks to bpf_map_charge_init() 2019-05-31 16:52:56 -07:00
lpm_trie.c bpf: move memory size checks to bpf_map_charge_init() 2019-05-31 16:52:56 -07:00
Makefile bpf: silence warning messages in core 2019-06-12 16:51:02 +02:00
map_in_map.c bpf: set inner_map_meta->spin_lock_off correctly 2019-02-27 17:03:13 -08:00
map_in_map.h bpf: Add syscall lookup support for fd array and htab 2017-06-29 13:13:25 -04:00
offload.c bpf: offload: add priv field for drivers 2019-02-12 17:07:09 +01:00
percpu_freelist.c bpf: fix lockdep false positive in percpu_freelist 2019-01-31 23:18:21 +01:00
percpu_freelist.h bpf: fix lockdep false positive in percpu_freelist 2019-01-31 23:18:21 +01:00
queue_stack_maps.c bpf: move memory size checks to bpf_map_charge_init() 2019-05-31 16:52:56 -07:00
reuseport_array.c bpf: move memory size checks to bpf_map_charge_init() 2019-05-31 16:52:56 -07:00
stackmap.c bpf: move memory size checks to bpf_map_charge_init() 2019-05-31 16:52:56 -07:00
syscall.c bpf: move memory size checks to bpf_map_charge_init() 2019-05-31 16:52:56 -07:00
tnum.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
verifier.c bpf: track spill/fill of constants 2019-06-19 02:22:51 +02:00
xskmap.c bpf: Allow bpf_map_lookup_elem() on an xskmap 2019-06-10 23:31:26 -07:00