bpf: Replace "want address" users of BPF_CAST_CALL with BPF_CALL_IMM

In order to keep ahead of cases in the kernel where Control Flow
Integrity (CFI) may trip over function call casts, enabling
-Wcast-function-type is helpful. To that end, BPF_CAST_CALL causes
various warnings and is one of the last places in the kernel triggering
this warning.

Most places using BPF_CAST_CALL actually just want a void * to perform
math on. It's not actually performing a call, so just use a different
helper to get the void *, by way of the new BPF_CALL_IMM() helper, which
can clean up a common copy/paste idiom as well.

This change results in no object code difference.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://github.com/KSPP/linux/issues/20
Link: https://lore.kernel.org/lkml/CAEf4Bzb46=-J5Fxc3mMZ8JQPtK1uoE0q6+g6WPz53Cvx=CBEhw@mail.gmail.com
Link: https://lore.kernel.org/bpf/20210928230946.4062144-2-keescook@chromium.org

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index 08f438e6fe9e..21ea1ab253a1 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -12439,7 +12439,7 @@ static __init int prepare_tail_call_tests(struct bpf_array **pprogs)
 					err = -EFAULT;
 					goto out_err;
 				}
-				*insn = BPF_EMIT_CALL(BPF_CAST_CALL(addr));
+				*insn = BPF_EMIT_CALL(addr);
 				if ((long)__bpf_call_base + insn->imm != addr)
 					*insn = BPF_JMP_A(0); /* Skip: NOP */
 				break;