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From ad23030b9029340bee87a03793aaaa98b1df8a18 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Wed, 18 Jan 2012 07:21:42 +0000
Subject: [PATCH 76/90] net: bpf_jit: fix divide by 0 generation
[ Upstream commit d00a9dd21bdf7908b70866794c8313ee8a5abd5c ]
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/net/bpf_jit_comp.c | 36 ++++++++++++++++++++++--------------
1 files changed, 22 insertions(+), 14 deletions(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 7b65f75..7c1b765 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -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) {
--
1.7.7.4
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