[PATCH 6.12 451/567] LoongArch: BPF: Sign extend kfunc call arguments

Greg Kroah-Hartman
2026-01-06T17:39:15Z

From: Hengqi Chen <hengqi.chen@gmail.com>

commit 3f5a238f24d7b75f9efe324d3539ad388f58536e upstream.

The kfunc calls are native calls so they should follow LoongArch calling
conventions. Sign extend its arguments properly to avoid kernel panic.
This is done by adding a new emit_abi_ext() helper. The emit_abi_ext()
helper performs extension in place meaning a value already store in the
target register (Note: this is different from the existing sign_extend()
helper and thus we can't reuse it).

Cc: stable@vger.kernel.org
Fixes: 5dc615520c4d ("LoongArch: Add BPF JIT support")
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/loongarch/net/bpf_jit.c | 16 ++++++++++++++++
arch/loongarch/net/bpf_jit.h | 26 ++++++++++++++++++++++++++
2 files changed, 42 insertions(+)

--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -897,6 +897,22 @@ static int build_insn(const struct bpf_i
if (ret < 0)
return ret;

+ if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
+ const struct btf_func_model *m;
+ int i;
+
+ m = bpf_jit_find_kfunc_model(ctx->prog, insn);
+ if (!m)
+ return -EINVAL;
+
+ for (i = 0; i < m->nr_args; i++) {
+ u8 reg = regmap[BPF_REG_1 + i];
+ bool sign = m->arg_flags[i] & BTF_FMODEL_SIGNED_ARG;
+
+ emit_abi_ext(ctx, reg, m->arg_size[i], sign);
+ }
+ }
+
move_addr(ctx, t1, func_addr);
emit_insn(ctx, jirl, LOONGARCH_GPR_RA, t1, 0);

--- a/arch/loongarch/net/bpf_jit.h
+++ b/arch/loongarch/net/bpf_jit.h
@@ -87,6 +87,32 @@ static inline void emit_sext_32(struct j
emit_insn(ctx, addiw, reg, reg, 0);
}

+/* Emit proper extension according to ABI requirements.
+ * Note that it requires a value of size `size` already resides in register `reg`.
+ */
+static inline void emit_abi_ext(struct jit_ctx *ctx, int reg, u8 size, bool sign)
+{
+ /* ABI requires unsigned char/short to be zero-extended */
+ if (!sign && (size == 1 || size == 2))
+ return;
+
+ switch (size) {
+ case 1:
+ emit_insn(ctx, extwb, reg, reg);
+ break;
+ case 2:
+ emit_insn(ctx, extwh, reg, reg);
+ break;
+ case 4:
+ emit_insn(ctx, addiw, reg, reg, 0);
+ break;
+ case 8:
+ break;
+ default:
+ pr_warn("bpf_jit: invalid size %d for extension\n", size);
+ }
+}
+
static inline void move_addr(struct jit_ctx *ctx, enum loongarch_gpr rd, u64 addr)
{
u64 imm_11_0, imm_31_12, imm_51_32, imm_63_52;