Commit 769e0de6 authored Nov 29, 2014 by Alexei Starovoitov Committed by David S. Miller Dec 05, 2014

bpf: x86: fix epilogue generation for eBPF programs



classic BPF has a restriction that last insn is always BPF_RET.
eBPF doesn't have BPF_RET instruction and this restriction.
It has BPF_EXIT insn which can appear anywhere in the program
one or more times and it doesn't have to be last insn.
Fix eBPF JIT to emit epilogue when first BPF_EXIT is seen
and all other BPF_EXIT instructions will be emitted as jump.

Since jump offset to epilogue is computed as:
jmp_offset = ctx->cleanup_addr - addrs[i]
we need to change type of cleanup_addr to signed to compute the offset as:
(long long) ((int)20 - (int)30)
instead of:
(long long) ((unsigned int)20 - (int)30)

Fixes: 62258278 ("net: filter: x86: internal BPF JIT")
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 6fb2a756

arch/x86/net/bpf_jit_comp.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -178,7 +178,7 @@ static void jit_fill_hole(void *area, unsigned int size)
		}

		struct jit_context {
		unsigned int cleanup_addr; /* epilogue code offset */
		int cleanup_addr; /* epilogue code offset */
		bool seen_ld_abs;
		};

		@@ -192,6 +192,7 @@ static int do_jit(struct bpf_prog bpf_prog, int addrs, u8 *image,
		struct bpf_insn *insn = bpf_prog->insnsi;
		int insn_cnt = bpf_prog->len;
		bool seen_ld_abs = ctx->seen_ld_abs \| (oldproglen == 0);
		bool seen_exit = false;
		u8 temp[BPF_MAX_INSN_SIZE + BPF_INSN_SAFETY];
		int i;
		int proglen = 0;
		@@ -854,10 +855,11 @@ xadd: if (is_imm8(insn->off))
		goto common_load;

		case BPF_JMP \| BPF_EXIT:
		if (i != insn_cnt - 1) {
		if (seen_exit) {
		jmp_offset = ctx->cleanup_addr - addrs[i];
		goto emit_jmp;
		}
		seen_exit = true;
		/* update cleanup_addr */
		ctx->cleanup_addr = proglen;
		/* mov rbx, qword ptr [rbp-X] */