bpf.c - platform/external/minijail - Gitiles

 /* Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */

 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

 #include "bpf.h"
 #include "util.h"

 /* Architecture validation. */
 size_t bpf_validate_arch(struct sock_filter *filter)
 {
 	struct sock_filter *curr_block = filter;
 	set_bpf_stmt(curr_block++, BPF_LD + BPF_W + BPF_ABS, arch_nr);
 	set_bpf_jump(curr_block++, BPF_JMP + BPF_JEQ + BPF_K, ARCH_NR, SKIP,
 		     NEXT);
 	set_bpf_ret_kill(curr_block++);
 	return curr_block - filter;
 }

 /* Syscall number eval functions. */
 size_t bpf_allow_syscall(struct sock_filter *filter, int nr)
 {
 	struct sock_filter *curr_block = filter;
 	set_bpf_jump(curr_block++, BPF_JMP + BPF_JEQ + BPF_K, nr, NEXT, SKIP);
 	set_bpf_stmt(curr_block++, BPF_RET + BPF_K, SECCOMP_RET_ALLOW);
 	return curr_block - filter;
 }

 size_t bpf_allow_syscall_args(struct sock_filter *filter, int nr,
 			      unsigned int id)
 {
 	struct sock_filter *curr_block = filter;
 	set_bpf_jump(curr_block++, BPF_JMP + BPF_JEQ + BPF_K, nr, NEXT, SKIP);
 	set_bpf_jump_lbl(curr_block++, id);
 	return curr_block - filter;
 }

 /* Size-aware arg loaders. */
 #if defined(BITS32)
 size_t bpf_load_arg(struct sock_filter *filter, int argidx)
 {
 	set_bpf_stmt(filter, BPF_LD + BPF_W + BPF_ABS, LO_ARG(argidx));
 	return 1U;
 }
 #elif defined(BITS64)
 size_t bpf_load_arg(struct sock_filter *filter, int argidx)
 {
 	struct sock_filter *curr_block = filter;
 	set_bpf_stmt(curr_block++, BPF_LD + BPF_W + BPF_ABS, LO_ARG(argidx));
 	set_bpf_stmt(curr_block++, BPF_ST, 0); /* lo -> M[0] */
 	set_bpf_stmt(curr_block++, BPF_LD + BPF_W + BPF_ABS, HI_ARG(argidx));
 	set_bpf_stmt(curr_block++, BPF_ST, 1); /* hi -> M[1] */
 	return curr_block - filter;
 }
 #endif

 /* Size-aware equality comparison. */
 size_t bpf_comp_jeq32(struct sock_filter *filter, unsigned long c,
 		      unsigned char jt, unsigned char jf)
 {
 	unsigned int lo = (unsigned int)(c & 0xFFFFFFFF);
 	set_bpf_jump(filter, BPF_JMP + BPF_JEQ + BPF_K, lo, jt, jf);
 	return 1U;
 }

 /*
  * On 64 bits, we have to do two 32-bit comparisons.
  * We jump true when *both* comparisons are true.
  */
 #if defined(BITS64)
 size_t bpf_comp_jeq64(struct sock_filter *filter, uint64_t c, unsigned char jt,
 		      unsigned char jf)
 {
 	unsigned int lo = (unsigned int)(c & 0xFFFFFFFF);
 	unsigned int hi = (unsigned int)(c >> 32);

 	struct sock_filter *curr_block = filter;

 	/* bpf_load_arg leaves |hi| in A */
 	curr_block += bpf_comp_jeq32(curr_block, hi, NEXT, SKIPN(2) + jf);
 	set_bpf_stmt(curr_block++, BPF_LD + BPF_MEM, 0); /* swap in |lo| */
 	curr_block += bpf_comp_jeq32(curr_block, lo, jt, jf);

 	return curr_block - filter;
 }
 #endif

 /* Size-aware bitwise AND. */
 size_t bpf_comp_jset32(struct sock_filter *filter, unsigned long mask,
 		       unsigned char jt, unsigned char jf)
 {
 	unsigned int mask_lo = (unsigned int)(mask & 0xFFFFFFFF);
 	set_bpf_jump(filter, BPF_JMP + BPF_JSET + BPF_K, mask_lo, jt, jf);
 	return 1U;
 }

 /*
  * On 64 bits, we have to do two 32-bit bitwise ANDs.
  * We jump true when *either* bitwise AND is true (non-zero).
  */
 #if defined(BITS64)
 size_t bpf_comp_jset64(struct sock_filter *filter, uint64_t mask,
 		       unsigned char jt, unsigned char jf)
 {
 	unsigned int mask_lo = (unsigned int)(mask & 0xFFFFFFFF);
 	unsigned int mask_hi = (unsigned int)(mask >> 32);

 	struct sock_filter *curr_block = filter;

 	/* bpf_load_arg leaves |hi| in A */
 	curr_block += bpf_comp_jset32(curr_block, mask_hi, SKIPN(2) + jt, NEXT);
 	set_bpf_stmt(curr_block++, BPF_LD + BPF_MEM, 0); /* swap in |lo| */
 	curr_block += bpf_comp_jset32(curr_block, mask_lo, jt, jf);

 	return curr_block - filter;
 }
 #endif

 size_t bpf_comp_jin(struct sock_filter *filter, unsigned long mask,
 		    unsigned char jt, unsigned char jf)
 {
 	unsigned long negative_mask = ~mask;
 	/*
 	 * The mask is negated, so the comparison will be true when the argument
 	 * includes a flag that wasn't listed in the original (non-negated)
 	 * mask. This would be the failure case, so we switch |jt| and |jf|.
 	 */
 	return bpf_comp_jset(filter, negative_mask, jf, jt);
 }

 size_t bpf_arg_comp(struct sock_filter **pfilter, int op, int argidx,
 		    unsigned long c, unsigned int label_id)
 {
 	struct sock_filter *filter =
 	    calloc(BPF_ARG_COMP_LEN + 1, sizeof(struct sock_filter));
 	struct sock_filter *curr_block = filter;
 	size_t (*comp_function)(struct sock_filter * filter, unsigned long k,
 				unsigned char jt, unsigned char jf);
 	int flip = 0;

 	/* Load arg */
 	curr_block += bpf_load_arg(curr_block, argidx);

 	/* Jump type */
 	switch (op) {
 	case EQ:
 		comp_function = bpf_comp_jeq;
 		flip = 0;
 		break;
 	case NE:
 		comp_function = bpf_comp_jeq;
 		flip = 1;
 		break;
 	case SET:
 		comp_function = bpf_comp_jset;
 		flip = 0;
 		break;
 	case IN:
 		comp_function = bpf_comp_jin;
 		flip = 0;
 		break;
 	default:
 		*pfilter = NULL;
 		return 0;
 	}

 	/*
 	 * It's easier for the rest of the code to have the true branch
 	 * skip and the false branch fall through.
 	 */
 	unsigned char jt = flip ? NEXT : SKIP;
 	unsigned char jf = flip ? SKIP : NEXT;
 	curr_block += comp_function(curr_block, c, jt, jf);
 	curr_block += set_bpf_jump_lbl(curr_block, label_id);

 	*pfilter = filter;
 	return curr_block - filter;
 }

 void dump_bpf_filter(struct sock_filter *filter, unsigned short len)
 {
 	int i = 0;

 	printf("len == %d\n", len);
 	printf("filter:\n");
 	for (i = 0; i < len; i++) {
 		printf("%d: \t{ code=%#x, jt=%u, jf=%u, k=%#x \t}\n", i,
 		       filter[i].code, filter[i].jt, filter[i].jf, filter[i].k);
 	}
 }

 void dump_bpf_prog(struct sock_fprog *fprog)
 {
 	struct sock_filter *filter = fprog->filter;
 	unsigned short len = fprog->len;
 	dump_bpf_filter(filter, len);
 }

 int bpf_resolve_jumps(struct bpf_labels *labels, struct sock_filter *filter,
 		      size_t len)
 {
 	struct sock_filter *instr;
 	size_t i, offset;

 	if (len > BPF_MAXINSNS)
 		return -1;

 	/*
 	 * Walk it once, backwards, to build the label table and do fixups.
 	 * Since backward jumps are disallowed by BPF, this is easy.
 	 */
 	for (i = 0; i < len; i++) {
 		offset = len - i - 1;
 		instr = &filter[offset];
 		if (instr->code != (BPF_JMP + BPF_JA))
 			continue;
 		switch ((instr->jt << 8) | instr->jf) {
 		case (JUMP_JT << 8) | JUMP_JF:
 			if (instr->k >= labels->count) {
 				warn("nonexistent label id: %u", instr->k);
 				return -1;
 			}
 			if (labels->labels[instr->k].location == 0xffffffff) {
 				warn("unresolved label: '%s'",
 				     labels->labels[instr->k].label);
 				return -1;
 			}
 			instr->k =
 			    labels->labels[instr->k].location - (offset + 1);
 			instr->jt = 0;
 			instr->jf = 0;
 			continue;
 		case (LABEL_JT << 8) | LABEL_JF:
 			if (labels->labels[instr->k].location != 0xffffffff) {
 				warn("duplicate label: '%s'",
 				     labels->labels[instr->k].label);
 				return -1;
 			}
 			labels->labels[instr->k].location = offset;
 			instr->k = 0; /* Fall through. */
 			instr->jt = 0;
 			instr->jf = 0;
 			continue;
 		}
 	}
 	return 0;
 }

 /* Simple lookup table for labels. */
 int bpf_label_id(struct bpf_labels *labels, const char *label)
 {
 	struct __bpf_label *begin = labels->labels, *end;
 	int id;
 	if (labels->count == 0) {
 		begin->label = strndup(label, MAX_BPF_LABEL_LEN);
 		if (!begin->label) {
 			return -1;
 		}
 		begin->location = 0xffffffff;
 		labels->count++;
 		return 0;
 	}
 	end = begin + labels->count;
 	for (id = 0; begin < end; ++begin, ++id) {
 		if (!strcmp(label, begin->label))
 			return id;
 	}

 	/* The label wasn't found. Insert it only if there's space. */
 	if (labels->count == BPF_LABELS_MAX) {
 		return -1;
 	}
 	begin->label = strndup(label, MAX_BPF_LABEL_LEN);
 	if (!begin->label) {
 		return -1;
 	}
 	begin->location = 0xffffffff;
 	labels->count++;
 	return id;
 }

 /* Free label strings. */
 void free_label_strings(struct bpf_labels *labels)
 {
 	if (labels->count == 0)
 		return;

 	struct __bpf_label *begin = labels->labels, *end;

 	end = begin + labels->count;
 	for (; begin < end; ++begin) {
 		if (begin->label)
 			free((void *)(begin->label));
 	}

 	labels->count = 0;
 }
	/* Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*/

	#include <stdint.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>

	#include "bpf.h"
	#include "util.h"

	/* Architecture validation. */
	size_t bpf_validate_arch(struct sock_filter *filter)
	{
	struct sock_filter *curr_block = filter;
	set_bpf_stmt(curr_block++, BPF_LD + BPF_W + BPF_ABS, arch_nr);
	set_bpf_jump(curr_block++, BPF_JMP + BPF_JEQ + BPF_K, ARCH_NR, SKIP,
	NEXT);
	set_bpf_ret_kill(curr_block++);
	return curr_block - filter;
	}

	/* Syscall number eval functions. */
	size_t bpf_allow_syscall(struct sock_filter *filter, int nr)
	{
	struct sock_filter *curr_block = filter;
	set_bpf_jump(curr_block++, BPF_JMP + BPF_JEQ + BPF_K, nr, NEXT, SKIP);
	set_bpf_stmt(curr_block++, BPF_RET + BPF_K, SECCOMP_RET_ALLOW);
	return curr_block - filter;
	}

	size_t bpf_allow_syscall_args(struct sock_filter *filter, int nr,
	unsigned int id)
	{
	struct sock_filter *curr_block = filter;
	set_bpf_jump(curr_block++, BPF_JMP + BPF_JEQ + BPF_K, nr, NEXT, SKIP);
	set_bpf_jump_lbl(curr_block++, id);
	return curr_block - filter;
	}

	/* Size-aware arg loaders. */
	#if defined(BITS32)
	size_t bpf_load_arg(struct sock_filter *filter, int argidx)
	{
	set_bpf_stmt(filter, BPF_LD + BPF_W + BPF_ABS, LO_ARG(argidx));
	return 1U;
	}
	#elif defined(BITS64)
	size_t bpf_load_arg(struct sock_filter *filter, int argidx)
	{
	struct sock_filter *curr_block = filter;
	set_bpf_stmt(curr_block++, BPF_LD + BPF_W + BPF_ABS, LO_ARG(argidx));
	set_bpf_stmt(curr_block++, BPF_ST, 0); /* lo -> M[0] */
	set_bpf_stmt(curr_block++, BPF_LD + BPF_W + BPF_ABS, HI_ARG(argidx));
	set_bpf_stmt(curr_block++, BPF_ST, 1); /* hi -> M[1] */
	return curr_block - filter;
	}
	#endif

	/* Size-aware equality comparison. */
	size_t bpf_comp_jeq32(struct sock_filter *filter, unsigned long c,
	unsigned char jt, unsigned char jf)
	{
	unsigned int lo = (unsigned int)(c & 0xFFFFFFFF);
	set_bpf_jump(filter, BPF_JMP + BPF_JEQ + BPF_K, lo, jt, jf);
	return 1U;
	}

	/*
	* On 64 bits, we have to do two 32-bit comparisons.
	* We jump true when both comparisons are true.
	*/
	#if defined(BITS64)
	size_t bpf_comp_jeq64(struct sock_filter *filter, uint64_t c, unsigned char jt,
	unsigned char jf)
	{
	unsigned int lo = (unsigned int)(c & 0xFFFFFFFF);
	unsigned int hi = (unsigned int)(c >> 32);

	struct sock_filter *curr_block = filter;

	/* bpf_load_arg leaves \|hi\| in A */
	curr_block += bpf_comp_jeq32(curr_block, hi, NEXT, SKIPN(2) + jf);
	set_bpf_stmt(curr_block++, BPF_LD + BPF_MEM, 0); /* swap in \|lo\| */
	curr_block += bpf_comp_jeq32(curr_block, lo, jt, jf);

	return curr_block - filter;
	}
	#endif

	/* Size-aware bitwise AND. */
	size_t bpf_comp_jset32(struct sock_filter *filter, unsigned long mask,
	unsigned char jt, unsigned char jf)
	{
	unsigned int mask_lo = (unsigned int)(mask & 0xFFFFFFFF);
	set_bpf_jump(filter, BPF_JMP + BPF_JSET + BPF_K, mask_lo, jt, jf);
	return 1U;
	}

	/*
	* On 64 bits, we have to do two 32-bit bitwise ANDs.
	* We jump true when either bitwise AND is true (non-zero).
	*/
	#if defined(BITS64)
	size_t bpf_comp_jset64(struct sock_filter *filter, uint64_t mask,
	unsigned char jt, unsigned char jf)
	{
	unsigned int mask_lo = (unsigned int)(mask & 0xFFFFFFFF);
	unsigned int mask_hi = (unsigned int)(mask >> 32);

	struct sock_filter *curr_block = filter;

	/* bpf_load_arg leaves \|hi\| in A */
	curr_block += bpf_comp_jset32(curr_block, mask_hi, SKIPN(2) + jt, NEXT);
	set_bpf_stmt(curr_block++, BPF_LD + BPF_MEM, 0); /* swap in \|lo\| */
	curr_block += bpf_comp_jset32(curr_block, mask_lo, jt, jf);

	return curr_block - filter;
	}
	#endif

	size_t bpf_comp_jin(struct sock_filter *filter, unsigned long mask,
	unsigned char jt, unsigned char jf)
	{
	unsigned long negative_mask = ~mask;
	/*
	* The mask is negated, so the comparison will be true when the argument
	* includes a flag that wasn't listed in the original (non-negated)
	* mask. This would be the failure case, so we switch \|jt\| and \|jf\|.
	*/
	return bpf_comp_jset(filter, negative_mask, jf, jt);
	}

	size_t bpf_arg_comp(struct sock_filter **pfilter, int op, int argidx,
	unsigned long c, unsigned int label_id)
	{
	struct sock_filter *filter =
	calloc(BPF_ARG_COMP_LEN + 1, sizeof(struct sock_filter));
	struct sock_filter *curr_block = filter;
	size_t (comp_function)(struct sock_filter filter, unsigned long k,
	unsigned char jt, unsigned char jf);
	int flip = 0;

	/* Load arg */
	curr_block += bpf_load_arg(curr_block, argidx);

	/* Jump type */
	switch (op) {
	case EQ:
	comp_function = bpf_comp_jeq;
	flip = 0;
	break;
	case NE:
	comp_function = bpf_comp_jeq;
	flip = 1;
	break;
	case SET:
	comp_function = bpf_comp_jset;
	flip = 0;
	break;
	case IN:
	comp_function = bpf_comp_jin;
	flip = 0;
	break;
	default:
	*pfilter = NULL;
	return 0;
	}

	/*
	* It's easier for the rest of the code to have the true branch
	* skip and the false branch fall through.
	*/
	unsigned char jt = flip ? NEXT : SKIP;
	unsigned char jf = flip ? SKIP : NEXT;
	curr_block += comp_function(curr_block, c, jt, jf);
	curr_block += set_bpf_jump_lbl(curr_block, label_id);

	*pfilter = filter;
	return curr_block - filter;
	}

	void dump_bpf_filter(struct sock_filter *filter, unsigned short len)
	{
	int i = 0;

	printf("len == %d\n", len);
	printf("filter:\n");
	for (i = 0; i < len; i++) {
	printf("%d: \t{ code=%#x, jt=%u, jf=%u, k=%#x \t}\n", i,
	filter[i].code, filter[i].jt, filter[i].jf, filter[i].k);
	}
	}

	void dump_bpf_prog(struct sock_fprog *fprog)
	{
	struct sock_filter *filter = fprog->filter;
	unsigned short len = fprog->len;
	dump_bpf_filter(filter, len);
	}

	int bpf_resolve_jumps(struct bpf_labels labels, struct sock_filter filter,
	size_t len)
	{
	struct sock_filter *instr;
	size_t i, offset;

	if (len > BPF_MAXINSNS)
	return -1;

	/*
	* Walk it once, backwards, to build the label table and do fixups.
	* Since backward jumps are disallowed by BPF, this is easy.
	*/
	for (i = 0; i < len; i++) {
	offset = len - i - 1;
	instr = &filter[offset];
	if (instr->code != (BPF_JMP + BPF_JA))
	continue;
	switch ((instr->jt << 8) \| instr->jf) {
	case (JUMP_JT << 8) \| JUMP_JF:
	if (instr->k >= labels->count) {
	warn("nonexistent label id: %u", instr->k);
	return -1;
	}
	if (labels->labels[instr->k].location == 0xffffffff) {
	warn("unresolved label: '%s'",
	labels->labels[instr->k].label);
	return -1;
	}
	instr->k =
	labels->labels[instr->k].location - (offset + 1);
	instr->jt = 0;
	instr->jf = 0;
	continue;
	case (LABEL_JT << 8) \| LABEL_JF:
	if (labels->labels[instr->k].location != 0xffffffff) {
	warn("duplicate label: '%s'",
	labels->labels[instr->k].label);
	return -1;
	}
	labels->labels[instr->k].location = offset;
	instr->k = 0; /* Fall through. */
	instr->jt = 0;
	instr->jf = 0;
	continue;
	}
	}
	return 0;
	}

	/* Simple lookup table for labels. */
	int bpf_label_id(struct bpf_labels labels, const char label)
	{
	struct __bpf_label begin = labels->labels, end;
	int id;
	if (labels->count == 0) {
	begin->label = strndup(label, MAX_BPF_LABEL_LEN);
	if (!begin->label) {
	return -1;
	}
	begin->location = 0xffffffff;
	labels->count++;
	return 0;
	}
	end = begin + labels->count;
	for (id = 0; begin < end; ++begin, ++id) {
	if (!strcmp(label, begin->label))
	return id;
	}

	/* The label wasn't found. Insert it only if there's space. */
	if (labels->count == BPF_LABELS_MAX) {
	return -1;
	}
	begin->label = strndup(label, MAX_BPF_LABEL_LEN);
	if (!begin->label) {
	return -1;
	}
	begin->location = 0xffffffff;
	labels->count++;
	return id;
	}

	/* Free label strings. */
	void free_label_strings(struct bpf_labels *labels)
	{
	if (labels->count == 0)
	return;

	struct __bpf_label begin = labels->labels, end;

	end = begin + labels->count;
	for (; begin < end; ++begin) {
	if (begin->label)
	free((void *)(begin->label));
	}

	labels->count = 0;
	}