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bpf: x86: fix epilogue generation for eBPF programs 

classic BPF has a restriction that last insn is always BPF_RET.
eBPF doesn't have BPF_RET instruction and this restriction.
It has BPF_EXIT insn which can appear anywhere in the program
one or more times and it doesn't have to be last insn.
Fix eBPF JIT to emit epilogue when first BPF_EXIT is seen
and all other BPF_EXIT instructions will be emitted as jump.

Since jump offset to epilogue is computed as:
jmp_offset = ctx->cleanup_addr - addrs[i]
we need to change type of cleanup_addr to signed to compute the offset as:
(long long) ((int)20 - (int)30)
instead of:
(long long) ((unsigned int)20 - (int)30)

Fixes: 622582786c ("net: filter: x86: internal BPF JIT")
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov 2014-11-29 14:46:13 -08:00 committed by David S. Miller
parent 6fb2a75673
commit 769e0de647
1 changed files with 4 additions and 2 deletions
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6
arch/x86/net/bpf_jit_comp.c
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@ -178,7 +178,7 @@ static void jit_fill_hole(void *area, unsigned int size)
}
struct jit_context {
unsigned int cleanup_addr; /* epilogue code offset */
int cleanup_addr; /* epilogue code offset */
bool seen_ld_abs;
};
@ -192,6 +192,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
struct bpf_insn *insn = bpf_prog->insnsi;
int insn_cnt = bpf_prog->len;
bool seen_ld_abs = ctx->seen_ld_abs | (oldproglen == 0);
bool seen_exit = false;
u8 temp[BPF_MAX_INSN_SIZE + BPF_INSN_SAFETY];
int i;
int proglen = 0;
@ -854,10 +855,11 @@ common_load:
goto common_load;
case BPF_JMP | BPF_EXIT:
if (i != insn_cnt - 1) {
if (seen_exit) {
jmp_offset = ctx->cleanup_addr - addrs[i];
goto emit_jmp;
}
seen_exit = true;
/* update cleanup_addr */
ctx->cleanup_addr = proglen;
/* mov rbx, qword ptr [rbp-X] */