bpf, arm64: Fix incorrect runtime stats

When __bpf_prog_enter() returns zero, the arm64 register x20 that stores
prog start time is not assigned to zero, causing incorrect runtime stats.

To fix it, assign the return value of bpf_prog_enter() to x20 register
immediately upon its return.

Fixes: efc9909fdce0 ("bpf, arm64: Add bpf trampoline for arm64")
Reported-by: Ivan Babrou <ivan@cloudflare.com>
Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Ivan Babrou <ivan@cloudflare.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240416064208.2919073-2-xukuohai@huaweicloud.com

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 122021f9bdfc87c3c9634d6801edad7845b9f96e..13eac43c632dfe793912ba310f7449d59e3bd9ed 100644 (file)
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -1844,15 +1844,15 @@ static void invoke_bpf_prog(struct jit_ctx *ctx, struct bpf_tramp_link *l,
 
        emit_call(enter_prog, ctx);
 
+       /* save return value to callee saved register x20 */
+       emit(A64_MOV(1, A64_R(20), A64_R(0)), ctx);
+
        /* if (__bpf_prog_enter(prog) == 0)
         *         goto skip_exec_of_prog;
         */
        branch = ctx->image + ctx->idx;
        emit(A64_NOP, ctx);
 
-       /* save return value to callee saved register x20 */
-       emit(A64_MOV(1, A64_R(20), A64_R(0)), ctx);
-
        emit(A64_ADD_I(1, A64_R(0), A64_SP, args_off), ctx);
        if (!p->jited)
                emit_addr_mov_i64(A64_R(1), (const u64)p->insnsi, ctx);