As an extension of [1], allow nocsr patterns recognition for kfuncs:
- pattern rules are the same as for helpers;
- spill/fill removal is allowed only for kfuncs marked with KF_NOCSR
flag;
Mark bpf_cast_to_kern_ctx() and bpf_rdonly_cast() kfuncs as KF_NOCSR
in order to conjure selftests for this feature.
After this patch-set verifier would rewrite the program below:
r2 = 1
*(u64 *)(r10 - 32) = r2
call %[bpf_cast_to_kern_ctx]
r2 = *(u64 *)(r10 - 32)
r0 = r2;"
As follows:
r2 = 1 /* spill/fill at r10[-32] is removed */
r0 = r1 /* replacement for bpf_cast_to_kern_ctx() */
r0 = r2
exit
[1] no_caller_saved_registers attribute for helper calls
https://lore.kernel.org/bpf/20240722233844.1406874-1-eddyz87@xxxxxxxxx/
Eduard Zingerman (3):
bpf: support nocsr patterns for calls to kfuncs
bpf: mark bpf_cast_to_kern_ctx and bpf_rdonly_cast as KF_NOCSR
selftests/bpf: check if nocsr pattern is recognized for kfuncs
include/linux/btf.h | 1 +
kernel/bpf/helpers.c | 4 +-
kernel/bpf/verifier.c | 37 ++++++++++++++
.../selftests/bpf/progs/verifier_nocsr.c | 50 +++++++++++++++++++
4 files changed, 90 insertions(+), 2 deletions(-)
--
2.45.2
