test_bpf: Add test to make conditional jump cross a large number of insns. (b7127cfe) · Commits · 戴 / test

On MIPS, conditional branches can only span 32k instructions. To exceed this limit in the JIT with the BPF maximum of 4k insns, we need to choose eBPF insns that expand to more than 8 machine instructions. Use BPF_LD_ABS as it is quite complex. This forces the JIT to invert the sense of the branch to branch around a long jump to the end. This (somewhat) verifies that the branch inversion logic and target address calculation of the long jumps are done correctly. Signed-off-by:

David Daney <david.daney@cavium.com> Acked-by:

Daniel Borkmann <daniel@iogearbox.net> Signed-off-by:

David S. Miller <davem@davemloft.net>

lib/test_bpf.c

+32 −0

Original line number	Diff line number	Diff line
		@@ -435,6 +435,30 @@ loop:
		return 0;
		}

		static int bpf_fill_jump_around_ld_abs(struct bpf_test *self)
		{
		unsigned int len = BPF_MAXINSNS;
		struct bpf_insn *insn;
		int i = 0;

		insn = kmalloc_array(len, sizeof(*insn), GFP_KERNEL);
		if (!insn)
		return -ENOMEM;

		insn[i++] = BPF_MOV64_REG(R6, R1);
		insn[i++] = BPF_LD_ABS(BPF_B, 0);
		insn[i] = BPF_JMP_IMM(BPF_JEQ, R0, 10, len - i - 2);
		i++;
		while (i < len - 1)
		insn[i++] = BPF_LD_ABS(BPF_B, 1);
		insn[i] = BPF_EXIT_INSN();

		self->u.ptr.insns = insn;
		self->u.ptr.len = len;

		return 0;
		}

		static int __bpf_fill_stxdw(struct bpf_test *self, int size)
		{
		unsigned int len = BPF_MAXINSNS;
		@@ -5044,6 +5068,14 @@ static struct bpf_test tests[] = {
		{ { ETH_HLEN, 0xbef } },
		.fill_helper = bpf_fill_ld_abs_vlan_push_pop,
		},
		{
		"BPF_MAXINSNS: jump around ld_abs",
		{ },
		INTERNAL,
		{ 10, 11 },
		{ { 2, 10 } },
		.fill_helper = bpf_fill_jump_around_ld_abs,
		},
		/*
		* LD_IND / LD_ABS on fragmented SKBs
		*/

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