On Fri, 31 May 2019 at 01:08, Song Liu [off-list ref] wrote:

On Thu, May 30, 2019 at 3:30 PM Luke Nelson [off-list ref] wrote:

quoted

In BPF, 32-bit ALU operations should zero-extend their results into
the 64-bit registers.

The current BPF JIT on RISC-V emits incorrect instructions that perform
sign extension only (e.g., addw, subw) on 32-bit add, sub, lsh, rsh,
arsh, and neg. This behavior diverges from the interpreter and JITs
for other architectures.

This patch fixes the bugs by performing zero extension on the destination
register of 32-bit ALU operations.

Fixes: 2353ecc6f91f ("bpf, riscv: add BPF JIT for RV64G")
Cc: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>

Acked-by: Song Liu <redacted>

Luke, thanks for fixing this! Nice work!

Acked-by: Björn Töpel <redacted>

quoted

---
The original patch is
https://lkml.org/lkml/2019/5/30/1370

This version is rebased against the bpf tree.
---
 arch/riscv/net/bpf_jit_comp.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/riscv/net/bpf_jit_comp.c b/arch/riscv/net/bpf_jit_comp.c
index e5c8d675bd6e..426d5c33ea90 100644
--- a/arch/riscv/net/bpf_jit_comp.c
+++ b/arch/riscv/net/bpf_jit_comp.c

@@ -751,10 +751,14 @@ static int emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
        case BPF_ALU | BPF_ADD | BPF_X:
        case BPF_ALU64 | BPF_ADD | BPF_X:
                emit(is64 ? rv_add(rd, rd, rs) : rv_addw(rd, rd, rs), ctx);
+               if (!is64)
+                       emit_zext_32(rd, ctx);
                break;
        case BPF_ALU | BPF_SUB | BPF_X:
        case BPF_ALU64 | BPF_SUB | BPF_X:
                emit(is64 ? rv_sub(rd, rd, rs) : rv_subw(rd, rd, rs), ctx);
+               if (!is64)
+                       emit_zext_32(rd, ctx);
                break;
        case BPF_ALU | BPF_AND | BPF_X:
        case BPF_ALU64 | BPF_AND | BPF_X:

@@ -795,14 +799,20 @@ static int emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
        case BPF_ALU | BPF_LSH | BPF_X:
        case BPF_ALU64 | BPF_LSH | BPF_X:
                emit(is64 ? rv_sll(rd, rd, rs) : rv_sllw(rd, rd, rs), ctx);
+               if (!is64)
+                       emit_zext_32(rd, ctx);
                break;
        case BPF_ALU | BPF_RSH | BPF_X:
        case BPF_ALU64 | BPF_RSH | BPF_X:
                emit(is64 ? rv_srl(rd, rd, rs) : rv_srlw(rd, rd, rs), ctx);
+               if (!is64)
+                       emit_zext_32(rd, ctx);
                break;
        case BPF_ALU | BPF_ARSH | BPF_X:
        case BPF_ALU64 | BPF_ARSH | BPF_X:
                emit(is64 ? rv_sra(rd, rd, rs) : rv_sraw(rd, rd, rs), ctx);
+               if (!is64)
+                       emit_zext_32(rd, ctx);
                break;

        /* dst = -dst */

@@ -810,6 +820,8 @@ static int emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
        case BPF_ALU64 | BPF_NEG:
                emit(is64 ? rv_sub(rd, RV_REG_ZERO, rd) :
                     rv_subw(rd, RV_REG_ZERO, rd), ctx);
+               if (!is64)
+                       emit_zext_32(rd, ctx);
                break;

        /* dst = BSWAP##imm(dst) */

@@ -964,14 +976,20 @@ static int emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
        case BPF_ALU | BPF_LSH | BPF_K:
        case BPF_ALU64 | BPF_LSH | BPF_K:
                emit(is64 ? rv_slli(rd, rd, imm) : rv_slliw(rd, rd, imm), ctx);
+               if (!is64)
+                       emit_zext_32(rd, ctx);
                break;
        case BPF_ALU | BPF_RSH | BPF_K:
        case BPF_ALU64 | BPF_RSH | BPF_K:
                emit(is64 ? rv_srli(rd, rd, imm) : rv_srliw(rd, rd, imm), ctx);
+               if (!is64)
+                       emit_zext_32(rd, ctx);
                break;
        case BPF_ALU | BPF_ARSH | BPF_K:
        case BPF_ALU64 | BPF_ARSH | BPF_K:
                emit(is64 ? rv_srai(rd, rd, imm) : rv_sraiw(rd, rd, imm), ctx);
+               if (!is64)
+                       emit_zext_32(rd, ctx);
                break;

        /* JUMP off */
--

2.19.1