Commit d00a9dd2 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net: bpf_jit: fix divide by 0 generation 



Several problems fixed in this patch :

1) Target of the conditional jump in case a divide by 0 is performed
   by a bpf is wrong.

2) Must 'generate' the full function prologue/epilogue at pass=0,
   or else we can stop too early in pass=1 if the proglen doesnt change.
   (if the increase of prologue/epilogue equals decrease of all
    instructions length because some jumps are converted to near jumps)

3) Change the wrong length detection at the end of code generation to
   issue a more explicit message, no need for a full stack trace.

Reported-by: default avatarPhil Oester <kernel@linuxace.com>
Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1c659a44

arch/x86/net/bpf_jit_comp.c

+22 −14
Original line number Diff line number Diff line
@@ -151,17 +151,18 @@ void bpf_jit_compile(struct sk_filter *fp) 
	cleanup_addr = proglen; /* epilogue address */



	for (pass = 0; pass < 10; pass++) {

		u8 seen_or_pass0 = (pass == 0) ? (SEEN_XREG | SEEN_DATAREF | SEEN_MEM) : seen;

		/* no prologue/epilogue for trivial filters (RET something) */

		proglen = 0;

		prog = temp;



		if (seen) {

		if (seen_or_pass0) {

			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))

			if (seen_or_pass0 & (SEEN_XREG | SEEN_DATAREF))

				EMIT4(0x48, 0x89, 0x5d, 0xf8); /* mov %rbx, -8(%rbp) */

			if (seen & SEEN_XREG)

			if (seen_or_pass0 & SEEN_XREG)

				CLEAR_X(); /* make sure we dont leek kernel memory */



			/*
@@ -170,7 +171,7 @@ void bpf_jit_compile(struct sk_filter *fp) 
			 *  r9 = skb->len - skb->data_len

			 *  r8 = skb->data

			 */

			if (seen & SEEN_DATAREF) {

			if (seen_or_pass0 & SEEN_DATAREF) {

				if (offsetof(struct sk_buff, len) <= 127)

					/* mov    off8(%rdi),%r9d */

					EMIT4(0x44, 0x8b, 0x4f, offsetof(struct sk_buff, len));
@@ -260,9 +261,14 @@ void bpf_jit_compile(struct sk_filter *fp) 
			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 {

				if (pc_ret0 > 0) {

					/* addrs[pc_ret0 - 1] is start address of target

					 * (addrs[i] - 4) is the address following this jmp

					 * ("xor %edx,%edx; div %ebx" being 4 bytes long)

					 */

					EMIT_COND_JMP(X86_JE, addrs[pc_ret0 - 1] -

								(addrs[i] - 4));

				} else {

					EMIT_COND_JMP(X86_JNE, 2 + 5);

					CLEAR_A();

					EMIT1_off32(0xe9, cleanup_addr - (addrs[i] - 4)); /* jmp .+off32 */
@@ -335,12 +341,12 @@ void bpf_jit_compile(struct sk_filter *fp) 
				}

				/* fallinto */

			case BPF_S_RET_A:

				if (seen) {

				if (seen_or_pass0) {

					if (i != flen - 1) {

						EMIT_JMP(cleanup_addr - addrs[i]);

						break;

					}

					if (seen & SEEN_XREG)

					if (seen_or_pass0 & SEEN_XREG)

						EMIT4(0x48, 0x8b, 0x5d, 0xf8);  /* mov  -8(%rbp),%rbx */

					EMIT1(0xc9);		/* leaveq */

				}
@@ -483,8 +489,9 @@ common_load: seen |= SEEN_DATAREF; 
				goto common_load;

			case BPF_S_LDX_B_MSH:

				if ((int)K < 0) {

					if (pc_ret0 != -1) {

						EMIT_JMP(addrs[pc_ret0] - addrs[i]);

					if (pc_ret0 > 0) {

						/* addrs[pc_ret0 - 1] is the start address */

						EMIT_JMP(addrs[pc_ret0 - 1] - addrs[i]);

						break;

					}

					CLEAR_A();
@@ -599,13 +606,14 @@ cond_branch: f_offset = addrs[i + filter[i].jf] - addrs[i]; 
		 * use it to give the cleanup instruction(s) addr

		 */

		cleanup_addr = proglen - 1; /* ret */

		if (seen)

		if (seen_or_pass0)

			cleanup_addr -= 1; /* leaveq */

		if (seen & SEEN_XREG)

		if (seen_or_pass0 & SEEN_XREG)

			cleanup_addr -= 4; /* mov  -8(%rbp),%rbx */



		if (image) {

			WARN_ON(proglen != oldproglen);

			if (proglen != oldproglen)

				pr_err("bpb_jit_compile proglen=%u != oldproglen=%u\n", proglen, oldproglen);

			break;

		}

		if (proglen == oldproglen) {

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