[PATCH v2 1/5] powerpc64/bpf: do not increment tailcall count when prog is NULL

Hari Bathini
2026-02-20T06:40:06Z

Do not increment tailcall count, if tailcall did not succeed due to
missing BPF program.

Fixes: ce0761419fae ("powerpc/bpf: Implement support for tail calls")
Cc: stable@vger.kernel.org
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---

* No changes since v1.

arch/powerpc/net/bpf_jit_comp64.c | 39 +++++++++++++++++--------------
1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index b1a3945ccc9f..44ce8a8783f9 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -522,9 +522,30 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o

/*
* tail_call_info++; <- Actual value of tcc here
+ * Writeback this updated value only if tailcall succeeds.
*/
EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), 1));

+ /* prog = array->ptrs[index]; */
+ EMIT(PPC_RAW_MULI(bpf_to_ppc(TMP_REG_2), b2p_index, 8));
+ EMIT(PPC_RAW_ADD(bpf_to_ppc(TMP_REG_2), bpf_to_ppc(TMP_REG_2), b2p_bpf_array));
+ EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_2), bpf_to_ppc(TMP_REG_2),
+ offsetof(struct bpf_array, ptrs)));
+
+ /*
+ * if (prog == NULL)
+ * goto out;
+ */
+ EMIT(PPC_RAW_CMPLDI(bpf_to_ppc(TMP_REG_2), 0));
+ PPC_BCC_SHORT(COND_EQ, out);
+
+ /* goto *(prog->bpf_func + prologue_size); */
+ EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_2), bpf_to_ppc(TMP_REG_2),
+ offsetof(struct bpf_prog, bpf_func)));
+ EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_2), bpf_to_ppc(TMP_REG_2),
+ FUNCTION_DESCR_SIZE + bpf_tailcall_prologue_size));
+ EMIT(PPC_RAW_MTCTR(bpf_to_ppc(TMP_REG_2)));
+
/*
* Before writing updated tail_call_info, distinguish if current frame
* is storing a reference to tail_call_info or actual tcc value in
@@ -539,24 +560,6 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
/* Writeback updated value to tail_call_info */
EMIT(PPC_RAW_STD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_2), 0));

- /* prog = array->ptrs[index]; */
- EMIT(PPC_RAW_MULI(bpf_to_ppc(TMP_REG_1), b2p_index, 8));
- EMIT(PPC_RAW_ADD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), b2p_bpf_array));
- EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), offsetof(struct bpf_array, ptrs)));
-
- /*
- * if (prog == NULL)
- * goto out;
- */
- EMIT(PPC_RAW_CMPLDI(bpf_to_ppc(TMP_REG_1), 0));
- PPC_BCC_SHORT(COND_EQ, out);
-
- /* goto *(prog->bpf_func + prologue_size); */
- EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), offsetof(struct bpf_prog, bpf_func)));
- EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1),
- FUNCTION_DESCR_SIZE + bpf_tailcall_prologue_size));
- EMIT(PPC_RAW_MTCTR(bpf_to_ppc(TMP_REG_1)));
-
/* tear down stack, restore NVRs, ... */
bpf_jit_emit_common_epilogue(image, ctx);

--
2.53.0