netdev - [RFC PATCH bpf-next v1 07/14] MIPS: eBPF: fix MOD64 insn on R6 ISA

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Date:   Sun, 11 Jul 2021 17:34:53 -0700
From:   Tony Ambardar <tony.ambardar@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>
Cc:     Tony Ambardar <Tony.Ambardar@...il.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-mips@...r.kernel.org,
        Johan Almbladh <johan.almbladh@...finetworks.com>,
        Hassan Naveed <hnaveed@...ecomp.com>,
        David Daney <ddaney@...iumnetworks.com>,
        Luke Nelson <luke.r.nels@...il.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>
Subject: [RFC PATCH bpf-next v1 07/14] MIPS: eBPF: fix MOD64 insn on R6 ISA

The BPF_ALU64 | BPF_MOD implementation is broken on MIPS64R6 due to use of
a 32-bit "modu" insn, as shown by the test_verifier failures:

  455/p MOD64 overflow, check 1 FAIL retval 0 != 1 (run 1/1)
  456/p MOD64 overflow, check 2 FAIL retval 0 != 1 (run 1/1)

Resolve by using the 64-bit "dmodu" instead.

Fixes: 6c2c8a188868 ("MIPS: eBPF: Provide eBPF support for MIPS64R6")
Signed-off-by: Tony Ambardar <Tony.Ambardar@...il.com>
---
 arch/mips/net/ebpf_jit.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/net/ebpf_jit.c b/arch/mips/net/ebpf_jit.c
index 4f641dcb2031..e8c403c6cfa3 100644
--- a/arch/mips/net/ebpf_jit.c
+++ b/arch/mips/net/ebpf_jit.c
@@ -800,7 +800,7 @@ static int build_one_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 			if (bpf_op == BPF_DIV)
 				emit_instr(ctx, ddivu_r6, dst, dst, MIPS_R_AT);
 			else
-				emit_instr(ctx, modu, dst, dst, MIPS_R_AT);
+				emit_instr(ctx, dmodu, dst, dst, MIPS_R_AT);
 			break;
 		}
 		emit_instr(ctx, ddivu, dst, MIPS_R_AT);
@@ -882,7 +882,7 @@ static int build_one_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 					emit_instr(ctx, ddivu_r6,
 							dst, dst, src);
 				else
-					emit_instr(ctx, modu, dst, dst, src);
+					emit_instr(ctx, dmodu, dst, dst, src);
 				break;
 			}
 			emit_instr(ctx, ddivu, dst, src);
-- 
2.25.1