x86,bpf: Avoid IBT objtool warning

[ Upstream commit be8a096521ca1a252bf078b347f96ce94582612e ]

Clang can inline emit_indirect_jump() and then folds constants, which
results in:

  | vmlinux.o: warning: objtool: emit_bpf_dispatcher()+0x6a4: relocation to !ENDBR: .text.__x86.indirect_thunk+0x40
  | vmlinux.o: warning: objtool: emit_bpf_dispatcher()+0x67d: relocation to !ENDBR: .text.__x86.indirect_thunk+0x40
  | vmlinux.o: warning: objtool: emit_bpf_tail_call_indirect()+0x386: relocation to !ENDBR: .text.__x86.indirect_thunk+0x20
  | vmlinux.o: warning: objtool: emit_bpf_tail_call_indirect()+0x35d: relocation to !ENDBR: .text.__x86.indirect_thunk+0x20

Suppress the optimization such that it must emit a code reference to
the __x86_indirect_thunk_array[] base.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lkml.kernel.org/r/20220405075531.GB30877@worktop.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 0ecb140864b21da1e6b9c4e8d22957c5a1012d07..b272e963388cb37f4ccb8b525d6c9161aaa2ae76 100644 (file)
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -398,6 +398,7 @@ static void emit_indirect_jump(u8 **pprog, int reg, u8 *ip)
                EMIT_LFENCE();
                EMIT2(0xFF, 0xE0 + reg);
        } else if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) {
+               OPTIMIZER_HIDE_VAR(reg);
                emit_jump(&prog, &__x86_indirect_thunk_array[reg], ip);
        } else
 #endif