Commit b54b6003 authored by Pu Lehui's avatar Pu Lehui Committed by Daniel Borkmann
Browse files

riscv, bpf: Emit fixed-length instructions for BPF_PSEUDO_FUNC 



For BPF_PSEUDO_FUNC instruction, verifier will refill imm with
correct addresses of bpf_calls and then run last pass of JIT.
Since the emit_imm of RV64 is variable-length, which will emit
appropriate length instructions accorroding to the imm, it may
broke ctx->offset, and lead to unpredictable problem, such as
inaccurate jump. So let's fix it with fixed-length instructions.

Fixes: 69c087ba ("bpf: Add bpf_for_each_map_elem() helper")
Suggested-by: default avatarBjörn Töpel <bjorn@rivosinc.com>
Signed-off-by: default avatarPu Lehui <pulehui@huawei.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarBjörn Töpel <bjorn@kernel.org>
Acked-by: default avatarBjörn Töpel <bjorn@kernel.org>
Link: https://lore.kernel.org/bpf/20221206091410.1584784-1-pulehui@huaweicloud.com
parent 08388efe

arch/riscv/net/bpf_jit_comp64.c

+28 −1
Original line number Diff line number Diff line
@@ -136,6 +136,25 @@ static bool in_auipc_jalr_range(s64 val) 
		val < ((1L << 31) - (1L << 11));

}



/* Emit fixed-length instructions for address */

static int emit_addr(u8 rd, u64 addr, bool extra_pass, struct rv_jit_context *ctx)

{

	u64 ip = (u64)(ctx->insns + ctx->ninsns);

	s64 off = addr - ip;

	s64 upper = (off + (1 << 11)) >> 12;

	s64 lower = off & 0xfff;



	if (extra_pass && !in_auipc_jalr_range(off)) {

		pr_err("bpf-jit: target offset 0x%llx is out of range\n", off);

		return -ERANGE;

	}



	emit(rv_auipc(rd, upper), ctx);

	emit(rv_addi(rd, rd, lower), ctx);

	return 0;

}



/* Emit variable-length instructions for 32-bit and 64-bit imm */

static void emit_imm(u8 rd, s64 val, struct rv_jit_context *ctx)

{

	/* Note that the immediate from the add is sign-extended,
@@ -1050,7 +1069,15 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx, 
		u64 imm64;



		imm64 = (u64)insn1.imm << 32 | (u32)imm;

		if (bpf_pseudo_func(insn)) {

			/* fixed-length insns for extra jit pass */

			ret = emit_addr(rd, imm64, extra_pass, ctx);

			if (ret)

				return ret;

		} else {

			emit_imm(rd, imm64, ctx);

		}



		return 1;

	}