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bpf, s390x: do not reload skb pointers in non-skb context

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The assumption of unconditionally reloading skb pointers on
BPF helper calls where bpf_helper_changes_pkt_data() holds
true is wrong. There can be different contexts where the
BPF helper would enforce a reload such as in case of XDP.
Here, we do have a struct xdp_buff instead of struct sk_buff
as context, thus this will access garbage.

JITs only ever need to deal with cached skb pointer reload
when ld_abs/ind was seen, therefore guard the reload behind
SEEN_SKB only. Tested on s390x.

Fixes: 9db7f2b818 ("s390/bpf: recache skb->data/hlen for skb_vlan_push/pop")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2017-12-14 21:07:23 +01:00 committed by Alexei Starovoitov
parent 2d17d8d79e
commit 6d59b7dbf7
1 changed files with 5 additions and 6 deletions
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11
arch/s390/net/bpf_jit_comp.c
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@ -55,8 +55,7 @@ struct bpf_jit {
#define SEEN_LITERAL 8 /* code uses literals */
#define SEEN_FUNC 16 /* calls C functions */
#define SEEN_TAIL_CALL 32 /* code uses tail calls */
#define SEEN_SKB_CHANGE 64 /* code changes skb data */
#define SEEN_REG_AX 128 /* code uses constant blinding */
#define SEEN_REG_AX 64 /* code uses constant blinding */
#define SEEN_STACK (SEEN_FUNC | SEEN_MEM | SEEN_SKB)
/*
@ -448,12 +447,12 @@ static void bpf_jit_prologue(struct bpf_jit *jit, u32 stack_depth)
EMIT6_DISP_LH(0xe3000000, 0x0024, REG_W1, REG_0,
REG_15, 152);
}
if (jit->seen & SEEN_SKB)
if (jit->seen & SEEN_SKB) {
emit_load_skb_data_hlen(jit);
if (jit->seen & SEEN_SKB_CHANGE)
/* stg %b1,ST_OFF_SKBP(%r0,%r15) */
EMIT6_DISP_LH(0xe3000000, 0x0024, BPF_REG_1, REG_0, REG_15,
STK_OFF_SKBP);
}
}
/*
@ -983,8 +982,8 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, int i
EMIT2(0x0d00, REG_14, REG_W1);
/* lgr %b0,%r2: load return value into %b0 */
EMIT4(0xb9040000, BPF_REG_0, REG_2);
if (bpf_helper_changes_pkt_data((void *)func)) {
jit->seen |= SEEN_SKB_CHANGE;
if ((jit->seen & SEEN_SKB) &&
bpf_helper_changes_pkt_data((void *)func)) {
/* lg %b1,ST_OFF_SKBP(%r15) */
EMIT6_DISP_LH(0xe3000000, 0x0004, BPF_REG_1, REG_0,
REG_15, STK_OFF_SKBP);