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[bpf-next,3/8] riscv, bpf: add support for far jumps and exits

Message ID 20191209173136.29615-4-bjorn.topel@gmail.com
State Changes Requested
Delegated to: BPF Maintainers
Headers show
Series riscv: BPF JIT fix, optimizations and far jumps support | expand

Commit Message

Björn Töpel Dec. 9, 2019, 5:31 p.m. UTC 
This commit add support for far (offset > 21b) jumps and exits.

Signed-off-by: Björn Töpel <bjorn.topel@gmail.com>
---
 arch/riscv/net/bpf_jit_comp.c | 37 ++++++++++++++++-------------------
 1 file changed, 17 insertions(+), 20 deletions(-)

Comments

Luke Nelson Dec. 9, 2019, 9:15 p.m. UTC | #1 
On Mon, Dec 9, 2019 at 9:32 AM Björn Töpel <bjorn.topel@gmail.com> wrote:
>
> This commit add support for far (offset > 21b) jumps and exits.
>
> Signed-off-by: Björn Töpel <bjorn.topel@gmail.com>

Similar to the other patch for far branching, we also used our tool
to formally verify this patch for far jumps:

https://github.com/uw-unsat/bpf-jit-verif/tree/far-jump-review


Reviewed-by: Luke Nelson <lukenels@cs.washington.edu>
Cc: Xi Wang <xi.wang@gmail.com>
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Patch

diff --git a/arch/riscv/net/bpf_jit_comp.c b/arch/riscv/net/bpf_jit_comp.c
index e2f6724b64f7..e9cc9832ac2c 100644
--- a/arch/riscv/net/bpf_jit_comp.c
+++ b/arch/riscv/net/bpf_jit_comp.c
@@ -506,16 +506,6 @@  static int is_13b_check(int off, int insn)
 	return 0;
 }
 
-static int is_21b_check(int off, int insn)
-{
-	if (!is_21b_int(off)) {
-		pr_err("bpf-jit: insn=%d 21b < offset=%d not supported yet!\n",
-		       insn, (int)off);
-		return -1;
-	}
-	return 0;
-}
-
 static void emit_imm(u8 rd, s64 val, struct rv_jit_context *ctx)
 {
 	/* Note that the immediate from the add is sign-extended,
@@ -733,6 +723,21 @@  static void emit_sext_32_rd(u8 *rd, struct rv_jit_context *ctx)
 	*rd = RV_REG_T2;
 }
 
+static void emit_jump_and_link(u8 rd, int rvoff, struct rv_jit_context *ctx)
+{
+	s64 upper, lower;
+
+	if (is_21b_int(rvoff)) {
+		emit(rv_jal(rd, rvoff >> 1), ctx);
+		return;
+	}
+
+	upper = (rvoff + (1 << 11)) >> 12;
+	lower = rvoff & 0xfff;
+	emit(rv_auipc(RV_REG_T1, upper), ctx);
+	emit(rv_jalr(rd, RV_REG_T1, lower), ctx);
+}
+
 /* return -1 or inverted cond */
 static int invert_bpf_cond(u8 cond)
 {
@@ -1117,13 +1122,7 @@  static int emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 	/* JUMP off */
 	case BPF_JMP | BPF_JA:
 		rvoff = rv_offset(i, off, ctx);
-		if (!is_21b_int(rvoff)) {
-			pr_err("bpf-jit: insn=%d offset=%d not supported yet!\n",
-			       i, rvoff);
-			return -1;
-		}
-
-		emit(rv_jal(RV_REG_ZERO, rvoff >> 1), ctx);
+		emit_jump_and_link(RV_REG_ZERO, rvoff, ctx);
 		break;
 
 	/* IF (dst COND src) JUMP off */
@@ -1261,9 +1260,7 @@  static int emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 			break;
 
 		rvoff = epilogue_offset(ctx);
-		if (is_21b_check(rvoff, i))
-			return -1;
-		emit(rv_jal(RV_REG_ZERO, rvoff >> 1), ctx);
+		emit_jump_and_link(RV_REG_ZERO, rvoff, ctx);
 		break;
 
 	/* dst = imm64 */