[PATCH bpf 4/5] bpf, sparc: fix usage of wrong reg for load_skb_regs after call

[Daniel Borkmann <daniel@iogearbox.net>]

When LD_ABS/IND is used in the program, and we have a BPF helper
call that changes packet data (bpf_helper_changes_pkt_data() returns
true), then in case of sparc JIT, we try to reload cached skb data
from bpf2sparc[BPF_REG_6]. However, there is no such guarantee or
assumption that skb sits in R6 at this point, all helpers changing
skb data only have a guarantee that skb sits in R1. Therefore,
store BPF R1 in L7 temporarily and after procedure call use L7 to
reload cached skb data. skb sitting in R6 is only true at the time
when LD_ABS/IND is executed.

Fixes: 7a12b5031c6b ("sparc64: Add eBPF JIT.")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
---
 arch/sparc/net/bpf_jit_comp_64.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/sparc/net/bpf_jit_comp_64.c b/arch/sparc/net/bpf_jit_comp_64.c
index 5765e7e..ff5f9cb 100644
--- a/arch/sparc/net/bpf_jit_comp_64.c
+++ b/arch/sparc/net/bpf_jit_comp_64.c
@@ -1245,14 +1245,16 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
 		u8 *func = ((u8 *)__bpf_call_base) + imm;
 
 		ctx->saw_call = true;
+		if (ctx->saw_ld_abs_ind && bpf_helper_changes_pkt_data(func))
+			emit_reg_move(bpf2sparc[BPF_REG_1], L7, ctx);
 
 		emit_call((u32 *)func, ctx);
 		emit_nop(ctx);
 
 		emit_reg_move(O0, bpf2sparc[BPF_REG_0], ctx);
 
-		if (bpf_helper_changes_pkt_data(func) && ctx->saw_ld_abs_ind)
-			load_skb_regs(ctx, bpf2sparc[BPF_REG_6]);
+		if (ctx->saw_ld_abs_ind && bpf_helper_changes_pkt_data(func))
+			load_skb_regs(ctx, L7);
 		break;
 	}
 
-- 
2.9.5