bpf: fix x64 JIT code generation for jmp to 1st insn (7c2e988f) · Commits · 戴 / test

Introduction of bounded loops exposed old bug in x64 JIT. JIT maintains the array of offsets to the end of all instructions to compute jmp offsets. addrs[0] - offset of the end of the 1st insn (that includes prologue). addrs[1] - offset of the end of the 2nd insn. JIT didn't keep the offset of the beginning of the 1st insn, since classic BPF didn't have backward jumps and valid extended BPF couldn't have a branch to 1st insn, because it didn't allow loops. With bounded loops it's possible to construct a valid program that jumps backwards to the 1st insn. Fix JIT by computing: addrs[0] - offset of the end of prologue == start of the 1st insn. addrs[1] - offset of the end of 1st insn. v1->v2: - Yonghong noticed a bug in jit linfo. Fix it by passing 'addrs + 1' to bpf_prog_fill_jited_linfo(), since it expects insn_to_jit_off array to be offsets to last byte. Reported-by:

<syzbot+35101610ff3e83119b1b@syzkaller.appspotmail.com> Fixes: ("bpf: introduce bounded loops") Fixes: ("net: filter: Just In Time compiler for x86-64") Signed-off-by:

Alexei Starovoitov <ast@kernel.org> Acked-by:

Song Liu <songliubraving@fb.com>

arch/x86/net/bpf_jit_comp.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -390,8 +390,9 @@ static int do_jit(struct bpf_prog bpf_prog, int addrs, u8 *image,

		emit_prologue(&prog, bpf_prog->aux->stack_depth,
		bpf_prog_was_classic(bpf_prog));
		addrs[0] = prog - temp;

		for (i = 0; i < insn_cnt; i++, insn++) {
		for (i = 1; i <= insn_cnt; i++, insn++) {
		const s32 imm32 = insn->imm;
		u32 dst_reg = insn->dst_reg;
		u32 src_reg = insn->src_reg;
		@@ -1105,7 +1106,7 @@ struct bpf_prog bpf_int_jit_compile(struct bpf_prog prog)
		extra_pass = true;
		goto skip_init_addrs;
		}
		addrs = kmalloc_array(prog->len, sizeof(*addrs), GFP_KERNEL);
		addrs = kmalloc_array(prog->len + 1, sizeof(*addrs), GFP_KERNEL);
		if (!addrs) {
		prog = orig_prog;
		goto out_addrs;
		@@ -1115,7 +1116,7 @@ struct bpf_prog bpf_int_jit_compile(struct bpf_prog prog)
		* Before first pass, make a rough estimation of addrs[]
		* each BPF instruction is translated to less than 64 bytes
		*/
		for (proglen = 0, i = 0; i < prog->len; i++) {
		for (proglen = 0, i = 0; i <= prog->len; i++) {
		proglen += 64;
		addrs[i] = proglen;
		}
		@@ -1180,7 +1181,7 @@ out_image:

		if (!image \|\| !prog->is_func \|\| extra_pass) {
		if (image)
		bpf_prog_fill_jited_linfo(prog, addrs);
		bpf_prog_fill_jited_linfo(prog, addrs + 1);
		out_addrs:
		kfree(addrs);
		kfree(jit_data);

Admin message