In some eBPF programs, the return value is a pointer.
When the kernel call an eBPF program (such as struct_ops),
it expects a 64-bit address to be returned, but instead a 32-bit value.
Before applying this patch:
./test_progs -a ns_bpf_qdisc
CPU 7 Unable to handle kernel paging request at virtual
address 0000000010440158.
As shown in the following test case,
bpf_fifo_dequeue return value is a pointer.
progs/bpf_qdisc_fifo.c
SEC("struct_ops/bpf_fifo_dequeue")
struct sk_buff *BPF_PROG(bpf_fifo_dequeue, struct Qdisc *sch)
{
struct sk_buff *skb = NULL;
........
skb = bpf_kptr_xchg(&skbn->skb, skb);
........
return skb;
}
kernel call bpf_fifo_dequeue：
net/sched/sch_generic.c
static struct sk_buff *dequeue_skb(struct Qdisc *q, bool *validate,
int *packets)
{
struct sk_buff *skb = NULL;
........
skb = q->dequeue(q);
.........
}
When accessing the skb, an address exception error will occur.
because the value returned by q->dequeue at this point is a 32-bit
address rather than a 64-bit address.
After applying the patch：
./test_progs -a ns_bpf_qdisc
Warning: sch_htb: quantum of class 10001 is small. Consider r2q change.
213/1 ns_bpf_qdisc/fifo:OK
213/2 ns_bpf_qdisc/fq:OK
213/3 ns_bpf_qdisc/attach to mq:OK
213/4 ns_bpf_qdisc/attach to non root:OK
213/5 ns_bpf_qdisc/incompl_ops:OK
213 ns_bpf_qdisc:OK
Summary: 1/5 PASSED, 0 SKIPPED, 0 FAILED
Fixes: 73c359d1d356 ("LoongArch: BPF: Sign-extend return values")
Signed-off-by: Jinyang He <hejinyang@xxxxxxxxxxx>
Signed-off-by: Haoran Jiang <jianghaoran@xxxxxxxxxx>
----------
v2:
1,add emit_slt* helpers
2,Use slt/slld/srad instructions to avoid branch
---
arch/loongarch/include/asm/inst.h | 8 ++++++++
arch/loongarch/net/bpf_jit.c | 17 +++++++++++++++--
2 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
index 277d2140676b..20f4fc745bea 100644
--- a/arch/loongarch/include/asm/inst.h
+++ b/arch/loongarch/include/asm/inst.h
@@ -92,6 +92,8 @@ enum reg2i6_op {
};
enum reg2i12_op {
+ slti_op = 0x08,
+ sltui_op = 0x09,
addiw_op = 0x0a,
addid_op = 0x0b,
lu52id_op = 0x0c,
@@ -148,6 +150,8 @@ enum reg3_op {
addd_op = 0x21,
subw_op = 0x22,
subd_op = 0x23,
+ slt_op = 0x24,
+ sltu_op = 0x25,
nor_op = 0x28,
and_op = 0x29,
or_op = 0x2a,
@@ -629,6 +633,8 @@ static inline void emit_##NAME(union loongarch_instruction *insn, \
insn->reg2i12_format.rj = rj; \
}
+DEF_EMIT_REG2I12_FORMAT(slti, slti_op)
+DEF_EMIT_REG2I12_FORMAT(sltui, sltui_op)
DEF_EMIT_REG2I12_FORMAT(addiw, addiw_op)
DEF_EMIT_REG2I12_FORMAT(addid, addid_op)
DEF_EMIT_REG2I12_FORMAT(lu52id, lu52id_op)
@@ -729,6 +735,8 @@ static inline void emit_##NAME(union loongarch_instruction *insn, \
DEF_EMIT_REG3_FORMAT(addw, addw_op)
DEF_EMIT_REG3_FORMAT(addd, addd_op)
DEF_EMIT_REG3_FORMAT(subd, subd_op)
+DEF_EMIT_REG3_FORMAT(slt, slt_op)
+DEF_EMIT_REG3_FORMAT(sltu, sltu_op)
DEF_EMIT_REG3_FORMAT(muld, muld_op)
DEF_EMIT_REG3_FORMAT(divd, divd_op)
DEF_EMIT_REG3_FORMAT(modd, modd_op)
diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index abfdb6bb5c38..50067be79c4f 100644
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -229,8 +229,21 @@ static void __build_epilogue(struct jit_ctx *ctx, bool is_tail_call)
emit_insn(ctx, addid, LOONGARCH_GPR_SP, LOONGARCH_GPR_SP, stack_adjust);
if (!is_tail_call) {
- /* Set return value */
- emit_insn(ctx, addiw, LOONGARCH_GPR_A0, regmap[BPF_REG_0], 0);
+ /*
+ * Set return value
+ * Check if the 64th bit in regmap[BPF_REG_0] is 1. If it is,
+ * the value in regmap[BPF_REG_0] is a kernel-space address.
+
+ * long long val = regmap[BPF_REG_0];
+ * int shift = 0 < val ? 32 : 0;
+ * return (val << shift) >> shift;
+ */
+ move_reg(ctx, LOONGARCH_GPR_A0, regmap[BPF_REG_0]);
+ emit_insn(ctx, slt, LOONGARCH_GPR_T0, LOONGARCH_GPR_ZERO, LOONGARCH_GPR_A0);
+ emit_insn(ctx, sllid, LOONGARCH_GPR_T0, LOONGARCH_GPR_T0, 5);
+ emit_insn(ctx, slld, LOONGARCH_GPR_A0, LOONGARCH_GPR_A0, LOONGARCH_GPR_T0);
+ emit_insn(ctx, srad, LOONGARCH_GPR_A0, LOONGARCH_GPR_A0, LOONGARCH_GPR_T0);
+
/* Return to the caller */
emit_insn(ctx, jirl, LOONGARCH_GPR_ZERO, LOONGARCH_GPR_RA, 0);
} else {
--
2.43.0
