Commit message: net: bpf_jit: fix an off-one bug in x86_64 cond jump target

x86 jump instruction size is 2 or 5 bytes (near/long jump), not 2 or 6
bytes.

In case a conditional jump is followed by a long jump, conditional jump
target is one byte past the start of target instruction.

Signed-off-by: Markus Kötter <nepenthesdev@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE: CVE-2014-2889
CWE: CWE-189
Vulnerability description: Off-by-one error in the bpf_jit_compile function in arch/x86/net/bpf_jit_comp.c in the Linux kernel before 3.1.8, when BPF JIT is enabled, allows local users to cause a denial of service (system crash) or possibly gain privileges via a long jump after a conditional jump.

Project: linux
File: bpf_jit_comp.c

void bpf_jit_compile(struct sk_filter *fp)
{
	u8 temp[64];
	u8 *prog;
	unsigned int proglen, oldproglen = 0;
	int ilen, i;
	int t_offset, f_offset;
	u8 t_op, f_op, seen = 0, pass;
	u8 *image = NULL;
	u8 *func;
	int pc_ret0 = -1; /* bpf index of first RET #0 instruction (if any) */
	unsigned int cleanup_addr; /* epilogue code offset */
	unsigned int *addrs;
	const struct sock_filter *filter = fp->insns;
	int flen = fp->len;

	if (!bpf_jit_enable)
		return;

	addrs = kmalloc(flen * sizeof(*addrs), GFP_KERNEL);
	if (addrs == NULL)
		return;

	/* 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 < flen; i++) {
		proglen += 64;
		addrs[i] = proglen;
	}
	cleanup_addr = proglen; /* epilogue address */

	for (pass = 0; pass < 10; pass++) {
		/* no prologue/epilogue for trivial filters (RET something) */
		proglen = 0;
		prog = temp;

		if (seen) {
			EMIT4(0x55, 0x48, 0x89, 0xe5); /* push %rbp; mov %rsp,%rbp */
			EMIT4(0x48, 0x83, 0xec, 96);	/* subq  $96,%rsp	*/
			/* note : must save %rbx in case bpf_error is hit */
			if (seen & (SEEN_XREG | SEEN_DATAREF))
				EMIT4(0x48, 0x89, 0x5d, 0xf8); /* mov %rbx, -8(%rbp) */
			if (seen & SEEN_XREG)
				CLEAR_X(); /* make sure we dont leek kernel memory */

			/*
			 * If this filter needs to access skb data,
			 * loads r9 and r8 with :
			 *  r9 = skb->len - skb->data_len
			 *  r8 = skb->data
			 */
			if (seen & SEEN_DATAREF) {
				if (offsetof(struct sk_buff, len) <= 127)
					/* mov    off8(%rdi),%r9d */
					EMIT4(0x44, 0x8b, 0x4f, offsetof(struct sk_buff, len));
				else {
					/* mov    off32(%rdi),%r9d */
					EMIT3(0x44, 0x8b, 0x8f);
					EMIT(offsetof(struct sk_buff, len), 4);
				}
				if (is_imm8(offsetof(struct sk_buff, data_len)))
					/* sub    off8(%rdi),%r9d */
					EMIT4(0x44, 0x2b, 0x4f, offsetof(struct sk_buff, data_len));
				else {
					EMIT3(0x44, 0x2b, 0x8f);
					EMIT(offsetof(struct sk_buff, data_len), 4);
				}

				if (is_imm8(offsetof(struct sk_buff, data)))
					/* mov off8(%rdi),%r8 */
					EMIT4(0x4c, 0x8b, 0x47, offsetof(struct sk_buff, data));
				else {
					/* mov off32(%rdi),%r8 */
					EMIT3(0x4c, 0x8b, 0x87);
					EMIT(offsetof(struct sk_buff, data), 4);
				}
			}
		}

		switch (filter[0].code) {
		case BPF_S_RET_K:
		case BPF_S_LD_W_LEN:
		case BPF_S_ANC_PROTOCOL:
		case BPF_S_ANC_IFINDEX:
		case BPF_S_ANC_MARK:
		case BPF_S_ANC_RXHASH:
		case BPF_S_ANC_CPU:
		case BPF_S_ANC_QUEUE:
		case BPF_S_LD_W_ABS:
		case BPF_S_LD_H_ABS:
		case BPF_S_LD_B_ABS:
			/* first instruction sets A register (or is RET 'constant') */
			break;
		default:
			/* make sure we dont leak kernel information to user */
			CLEAR_A(); /* A = 0 */
		}

		for (i = 0; i < flen; i++) {
			unsigned int K = filter[i].k;

			switch (filter[i].code) {
			case BPF_S_ALU_ADD_X: /* A += X; */
				seen |= SEEN_XREG;
				EMIT2(0x01, 0xd8);		/* add %ebx,%eax */
				break;
			case BPF_S_ALU_ADD_K: /* A += K; */
				if (!K)
					break;
				if (is_imm8(K))
					EMIT3(0x83, 0xc0, K);	/* add imm8,%eax */
				else
					EMIT1_off32(0x05, K);	/* add imm32,%eax */
				break;
			case BPF_S_ALU_SUB_X: /* A -= X; */
				seen |= SEEN_XREG;
				EMIT2(0x29, 0xd8);		/* sub    %ebx,%eax */
				break;
			case BPF_S_ALU_SUB_K: /* A -= K */
				if (!K)
					break;
				if (is_imm8(K))
					EMIT3(0x83, 0xe8, K); /* sub imm8,%eax */
				else
					EMIT1_off32(0x2d, K); /* sub imm32,%eax */
				break;
			case BPF_S_ALU_MUL_X: /* A *= X; */
				seen |= SEEN_XREG;
				EMIT3(0x0f, 0xaf, 0xc3);	/* imul %ebx,%eax */
				break;
			case BPF_S_ALU_MUL_K: /* A *= K */
				if (is_imm8(K))
					EMIT3(0x6b, 0xc0, K); /* imul imm8,%eax,%eax */
				else {
					EMIT2(0x69, 0xc0);		/* imul imm32,%eax */
					EMIT(K, 4);
				}
				break;
			case BPF_S_ALU_DIV_X: /* A /= X; */
				seen |= SEEN_XREG;
				EMIT2(0x85, 0xdb);	/* test %ebx,%ebx */
				if (pc_ret0 != -1)
					EMIT_COND_JMP(X86_JE, addrs[pc_ret0] - (addrs[i] - 4));
				else {
					EMIT_COND_JMP(X86_JNE, 2 + 5);
					CLEAR_A();
					EMIT1_off32(0xe9, cleanup_addr - (addrs[i] - 4)); /* jmp .+off32 */
				}
				EMIT4(0x31, 0xd2, 0xf7, 0xf3); /* xor %edx,%edx; div %ebx */
				break;
			case BPF_S_ALU_DIV_K: /* A = reciprocal_divide(A, K); */
				EMIT3(0x48, 0x69, 0xc0); /* imul imm32,%rax,%rax */
				EMIT(K, 4);
				EMIT4(0x48, 0xc1, 0xe8, 0x20); /* shr $0x20,%rax */
				break;
			case BPF_S_ALU_AND_X:
				seen |= SEEN_XREG;
				EMIT2(0x21, 0xd8);		/* and %ebx,%eax */
				break;
			case BPF_S_ALU_AND_K:
				if (K >= 0xFFFFFF00) {
					EMIT2(0x24, K & 0xFF); /* and imm8,%al */
				} else if (K >= 0xFFFF0000) {
					EMIT2(0x66, 0x25);	/* and imm16,%ax */
					EMIT2(K, 2);
				} else {
					EMIT1_off32(0x25, K);	/* and imm32,%eax */
				}
				break;
			case BPF_S_ALU_OR_X:
				seen |= SEEN_XREG;
				EMIT2(0x09, 0xd8);		/* or %ebx,%eax */
				break;
			case BPF_S_ALU_OR_K:
				if (is_imm8(K))
					EMIT3(0x83, 0xc8, K); /* or imm8,%eax */
				else
					EMIT1_off32(0x0d, K);	/* or imm32,%eax */
				break;
			case BPF_S_ALU_LSH_X: /* A <<= X; */
				seen |= SEEN_XREG;
				EMIT4(0x89, 0xd9, 0xd3, 0xe0);	/* mov %ebx,%ecx; shl %cl,%eax */
				break;
			case BPF_S_ALU_LSH_K:
				if (K == 0)
					break;
				else if (K == 1)
					EMIT2(0xd1, 0xe0); /* shl %eax */
				else
					EMIT3(0xc1, 0xe0, K);
				break;
			case BPF_S_ALU_RSH_X: /* A >>= X; */
				seen |= SEEN_XREG;
				EMIT4(0x89, 0xd9, 0xd3, 0xe8);	/* mov %ebx,%ecx; shr %cl,%eax */
				break;
			case BPF_S_ALU_RSH_K: /* A >>= K; */
				if (K == 0)
					break;
				else if (K == 1)
					EMIT2(0xd1, 0xe8); /* shr %eax */
				else
					EMIT3(0xc1, 0xe8, K);
				break;
			case BPF_S_ALU_NEG:
				EMIT2(0xf7, 0xd8);		/* neg %eax */
				break;
			case BPF_S_RET_K:
				if (!K) {
					if (pc_ret0 == -1)
						pc_ret0 = i;
					CLEAR_A();
				} else {
					EMIT1_off32(0xb8, K);	/* mov $imm32,%eax */
				}
				/* fallinto */
			case BPF_S_RET_A:
				if (seen) {
					if (i != flen - 1) {
						EMIT_JMP(cleanup_addr - addrs[i]);
						break;
					}
					if (seen & SEEN_XREG)
						EMIT4(0x48, 0x8b, 0x5d, 0xf8);  /* mov  -8(%rbp),%rbx */
					EMIT1(0xc9);		/* leaveq */
				}
				EMIT1(0xc3);		/* ret */
				break;
			case BPF_S_MISC_TAX: /* X = A */
				seen |= SEEN_XREG;
				EMIT2(0x89, 0xc3);	/* mov    %eax,%ebx */
				break;
			case BPF_S_MISC_TXA: /* A = X */
				seen |= SEEN_XREG;
				EMIT2(0x89, 0xd8);	/* mov    %ebx,%eax */
				break;
			case BPF_S_LD_IMM: /* A = K */
				if (!K)
					CLEAR_A();
				else
					EMIT1_off32(0xb8, K); /* mov $imm32,%eax */
				break;
			case BPF_S_LDX_IMM: /* X = K */
				seen |= SEEN_XREG;
				if (!K)
					CLEAR_X();
				else
					EMIT1_off32(0xbb, K); /* mov $imm32,%ebx */
				break;
			case BPF_S_LD_MEM: /* A = mem[K] : mov off8(%rbp),%eax */
				seen |= SEEN_MEM;
				EMIT3(0x8b, 0x45, 0xf0 - K*4);
				break;
			case BPF_S_LDX_MEM: /* X = mem[K] : mov off8(%rbp),%ebx */
				seen |= SEEN_XREG | SEEN_MEM;
				EMIT3(0x8b, 0x5d, 0xf0 - K*4);
				break;
			case BPF_S_ST: /* mem[K] = A : mov %eax,off8(%rbp) */
				seen |= SEEN_MEM;
				EMIT3(0x89, 0x45, 0xf0 - K*4);
				break;
			case BPF_S_STX: /* mem[K] = X : mov %ebx,off8(%rbp) */
				seen |= SEEN_XREG | SEEN_MEM;
				EMIT3(0x89, 0x5d, 0xf0 - K*4);
				break;
			case BPF_S_LD_W_LEN: /*	A = skb->len; */
				BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4);
				if (is_imm8(offsetof(struct sk_buff, len)))
					/* mov    off8(%rdi),%eax */
					EMIT3(0x8b, 0x47, offsetof(struct sk_buff, len));
				else {
					EMIT2(0x8b, 0x87);
					EMIT(offsetof(struct sk_buff, len), 4);
				}
				break;
			case BPF_S_LDX_W_LEN: /* X = skb->len; */
				seen |= SEEN_XREG;
				if (is_imm8(offsetof(struct sk_buff, len)))
					/* mov off8(%rdi),%ebx */
					EMIT3(0x8b, 0x5f, offsetof(struct sk_buff, len));
				else {
					EMIT2(0x8b, 0x9f);
					EMIT(offsetof(struct sk_buff, len), 4);
				}
				break;
			case BPF_S_ANC_PROTOCOL: /* A = ntohs(skb->protocol); */
				BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, protocol) != 2);
				if (is_imm8(offsetof(struct sk_buff, protocol))) {
					/* movzwl off8(%rdi),%eax */
					EMIT4(0x0f, 0xb7, 0x47, offsetof(struct sk_buff, protocol));
				} else {
					EMIT3(0x0f, 0xb7, 0x87); /* movzwl off32(%rdi),%eax */
					EMIT(offsetof(struct sk_buff, protocol), 4);
				}
				EMIT2(0x86, 0xc4); /* ntohs() : xchg   %al,%ah */
				break;
			case BPF_S_ANC_IFINDEX:
				if (is_imm8(offsetof(struct sk_buff, dev))) {
					/* movq off8(%rdi),%rax */
					EMIT4(0x48, 0x8b, 0x47, offsetof(struct sk_buff, dev));
				} else {
					EMIT3(0x48, 0x8b, 0x87); /* movq off32(%rdi),%rax */
					EMIT(offsetof(struct sk_buff, dev), 4);
				}
				EMIT3(0x48, 0x85, 0xc0);	/* test %rax,%rax */
				EMIT_COND_JMP(X86_JE, cleanup_addr - (addrs[i] - 6));
				BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, ifindex) != 4);
				EMIT2(0x8b, 0x80);	/* mov off32(%rax),%eax */
				EMIT(offsetof(struct net_device, ifindex), 4);
				break;
			case BPF_S_ANC_MARK:
				BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
				if (is_imm8(offsetof(struct sk_buff, mark))) {
					/* mov off8(%rdi),%eax */
					EMIT3(0x8b, 0x47, offsetof(struct sk_buff, mark));
				} else {
					EMIT2(0x8b, 0x87);
					EMIT(offsetof(struct sk_buff, mark), 4);
				}
				break;
			case BPF_S_ANC_RXHASH:
				BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, rxhash) != 4);
				if (is_imm8(offsetof(struct sk_buff, rxhash))) {
					/* mov off8(%rdi),%eax */
					EMIT3(0x8b, 0x47, offsetof(struct sk_buff, rxhash));
				} else {
					EMIT2(0x8b, 0x87);
					EMIT(offsetof(struct sk_buff, rxhash), 4);
				}
				break;
			case BPF_S_ANC_QUEUE:
				BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, queue_mapping) != 2);
				if (is_imm8(offsetof(struct sk_buff, queue_mapping))) {
					/* movzwl off8(%rdi),%eax */
					EMIT4(0x0f, 0xb7, 0x47, offsetof(struct sk_buff, queue_mapping));
				} else {
					EMIT3(0x0f, 0xb7, 0x87); /* movzwl off32(%rdi),%eax */
					EMIT(offsetof(struct sk_buff, queue_mapping), 4);
				}
				break;
			case BPF_S_ANC_CPU:
#ifdef CONFIG_SMP
				EMIT4(0x65, 0x8b, 0x04, 0x25); /* mov %gs:off32,%eax */
				EMIT((u32)(unsigned long)&cpu_number, 4); /* A = smp_processor_id(); */
#else
				CLEAR_A();
#endif
				break;
			case BPF_S_LD_W_ABS:
				func = sk_load_word;
common_load:			seen |= SEEN_DATAREF;
				if ((int)K < 0)
					goto out;
				t_offset = func - (image + addrs[i]);
				EMIT1_off32(0xbe, K); /* mov imm32,%esi */
				EMIT1_off32(0xe8, t_offset); /* call */
				break;
			case BPF_S_LD_H_ABS:
				func = sk_load_half;
				goto common_load;
			case BPF_S_LD_B_ABS:
				func = sk_load_byte;
				goto common_load;
			case BPF_S_LDX_B_MSH:
				if ((int)K < 0) {
					if (pc_ret0 != -1) {
						EMIT_JMP(addrs[pc_ret0] - addrs[i]);
						break;
					}
					CLEAR_A();
					EMIT_JMP(cleanup_addr - addrs[i]);
					break;
				}
				seen |= SEEN_DATAREF | SEEN_XREG;
				t_offset = sk_load_byte_msh - (image + addrs[i]);
				EMIT1_off32(0xbe, K);	/* mov imm32,%esi */
				EMIT1_off32(0xe8, t_offset); /* call sk_load_byte_msh */
				break;
			case BPF_S_LD_W_IND:
				func = sk_load_word_ind;
common_load_ind:		seen |= SEEN_DATAREF | SEEN_XREG;
				t_offset = func - (image + addrs[i]);
				EMIT1_off32(0xbe, K);	/* mov imm32,%esi   */
				EMIT1_off32(0xe8, t_offset);	/* call sk_load_xxx_ind */
				break;
			case BPF_S_LD_H_IND:
				func = sk_load_half_ind;
				goto common_load_ind;
			case BPF_S_LD_B_IND:
				func = sk_load_byte_ind;
				goto common_load_ind;
			case BPF_S_JMP_JA:
				t_offset = addrs[i + K] - addrs[i];
				EMIT_JMP(t_offset);
				break;
			COND_SEL(BPF_S_JMP_JGT_K, X86_JA, X86_JBE);
			COND_SEL(BPF_S_JMP_JGE_K, X86_JAE, X86_JB);
			COND_SEL(BPF_S_JMP_JEQ_K, X86_JE, X86_JNE);
			COND_SEL(BPF_S_JMP_JSET_K,X86_JNE, X86_JE);
			COND_SEL(BPF_S_JMP_JGT_X, X86_JA, X86_JBE);
			COND_SEL(BPF_S_JMP_JGE_X, X86_JAE, X86_JB);
			COND_SEL(BPF_S_JMP_JEQ_X, X86_JE, X86_JNE);
			COND_SEL(BPF_S_JMP_JSET_X,X86_JNE, X86_JE);

cond_branch:			f_offset = addrs[i + filter[i].jf] - addrs[i];
				t_offset = addrs[i + filter[i].jt] - addrs[i];

				/* same targets, can avoid doing the test :) */
				if (filter[i].jt == filter[i].jf) {
					EMIT_JMP(t_offset);
					break;
				}

				switch (filter[i].code) {
				case BPF_S_JMP_JGT_X:
				case BPF_S_JMP_JGE_X:
				case BPF_S_JMP_JEQ_X:
					seen |= SEEN_XREG;
					EMIT2(0x39, 0xd8); /* cmp %ebx,%eax */
					break;
				case BPF_S_JMP_JSET_X:
					seen |= SEEN_XREG;
					EMIT2(0x85, 0xd8); /* test %ebx,%eax */
					break;
				case BPF_S_JMP_JEQ_K:
					if (K == 0) {
						EMIT2(0x85, 0xc0); /* test   %eax,%eax */
						break;
					}
				case BPF_S_JMP_JGT_K:
				case BPF_S_JMP_JGE_K:
					if (K <= 127)
						EMIT3(0x83, 0xf8, K); /* cmp imm8,%eax */
					else
						EMIT1_off32(0x3d, K); /* cmp imm32,%eax */
					break;
				case BPF_S_JMP_JSET_K:
					if (K <= 0xFF)
						EMIT2(0xa8, K); /* test imm8,%al */
					else if (!(K & 0xFFFF00FF))
						EMIT3(0xf6, 0xc4, K >> 8); /* test imm8,%ah */
					else if (K <= 0xFFFF) {
						EMIT2(0x66, 0xa9); /* test imm16,%ax */
						EMIT(K, 2);
					} else {
						EMIT1_off32(0xa9, K); /* test imm32,%eax */
					}
 					break;
 				}
 				if (filter[i].jt != 0) {
					if (filter[i].jf)
						t_offset += is_near(f_offset) ? 2 : 6;
 					EMIT_COND_JMP(t_op, t_offset);
 					if (filter[i].jf)
 						EMIT_JMP(f_offset);
					break;
				}
				EMIT_COND_JMP(f_op, f_offset);
				break;
			default:
				/* hmm, too complex filter, give up with jit compiler */
				goto out;
			}
			ilen = prog - temp;
			if (image) {
				if (unlikely(proglen + ilen > oldproglen)) {
					pr_err("bpb_jit_compile fatal error\n");
					kfree(addrs);
					module_free(NULL, image);
					return;
				}
				memcpy(image + proglen, temp, ilen);
			}
			proglen += ilen;
			addrs[i] = proglen;
			prog = temp;
		}
		/* last bpf instruction is always a RET :
		 * use it to give the cleanup instruction(s) addr
		 */
		cleanup_addr = proglen - 1; /* ret */
		if (seen)
			cleanup_addr -= 1; /* leaveq */
		if (seen & SEEN_XREG)
			cleanup_addr -= 4; /* mov  -8(%rbp),%rbx */

		if (image) {
			WARN_ON(proglen != oldproglen);
			break;
		}
		if (proglen == oldproglen) {
			image = module_alloc(max_t(unsigned int,
						   proglen,
						   sizeof(struct work_struct)));
			if (!image)
				goto out;
		}
		oldproglen = proglen;
	}
	if (bpf_jit_enable > 1)
		pr_err("flen=%d proglen=%u pass=%d image=%p\n",
		       flen, proglen, pass, image);

	if (image) {
		if (bpf_jit_enable > 1)
			print_hex_dump(KERN_ERR, "JIT code: ", DUMP_PREFIX_ADDRESS,
				       16, 1, image, proglen, false);

		bpf_flush_icache(image, image + proglen);

		fp->bpf_func = (void *)image;
	}
out:
	kfree(addrs);
	return;
}