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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: Phil Oester <kernel@linuxace.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2012-01-18 07:21:42 +00:00 committed by David S. Miller
parent 1c659a4475
commit d00a9dd21b
1 changed files with 22 additions and 14 deletions
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36
arch/x86/net/bpf_jit_comp.c
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@ -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) {