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s390/bpf: recache skb->data/hlen for skb_vlan_push/pop
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Allow eBPF programs attached to TC qdiscs call skb_vlan_push/pop
via helper functions. These functions may change skb->data/hlen.
This data is cached by s390 JIT to improve performance of ld_abs/ld_ind
instructions. Therefore after a change we have to reload the data.

In case of usage of skb_vlan_push/pop, in the prologue we store
the SKB pointer on the stack and restore it after BPF_JMP_CALL
to skb_vlan_push/pop.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Michael Holzheu authored and David S. Miller committed Jul 29, 2015
1 parent cde66c2 commit 9db7f2b
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Showing 2 changed files with 37 additions and 23 deletions.
5 changes: 4 additions & 1 deletion arch/s390/net/bpf_jit.h
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,8 @@ extern u8 sk_load_word[], sk_load_half[], sk_load_byte[];
* | BPF stack | |
* | | |
* +---------------+ |
* | 8 byte skbp | |
* R15+170 -> +---------------+ |
* | 8 byte hlen | |
* R15+168 -> +---------------+ |
* | 4 byte align | |
Expand All @@ -51,11 +53,12 @@ extern u8 sk_load_word[], sk_load_half[], sk_load_byte[];
* We get 160 bytes stack space from calling function, but only use
* 12 * 8 byte for old backchain, r15..r6, and tail_call_cnt.
*/
#define STK_SPACE (MAX_BPF_STACK + 8 + 4 + 4 + 160)
#define STK_SPACE (MAX_BPF_STACK + 8 + 8 + 4 + 4 + 160)
#define STK_160_UNUSED (160 - 12 * 8)
#define STK_OFF (STK_SPACE - STK_160_UNUSED)
#define STK_OFF_TMP 160 /* Offset of tmp buffer on stack */
#define STK_OFF_HLEN 168 /* Offset of SKB header length on stack */
#define STK_OFF_SKBP 170 /* Offset of SKB pointer on stack */

#define STK_OFF_R6 (160 - 11 * 8) /* Offset of r6 on stack */
#define STK_OFF_TCCNT (160 - 12 * 8) /* Offset of tail_call_cnt on stack */
Expand Down
55 changes: 33 additions & 22 deletions arch/s390/net/bpf_jit_comp.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,7 @@ 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_STACK (SEEN_FUNC | SEEN_MEM | SEEN_SKB)

/*
Expand Down Expand Up @@ -381,6 +382,26 @@ static void save_restore_regs(struct bpf_jit *jit, int op)
} while (re <= 15);
}

/*
* For SKB access %b1 contains the SKB pointer. For "bpf_jit.S"
* we store the SKB header length on the stack and the SKB data
* pointer in REG_SKB_DATA.
*/
static void emit_load_skb_data_hlen(struct bpf_jit *jit)
{
/* Header length: llgf %w1,<len>(%b1) */
EMIT6_DISP_LH(0xe3000000, 0x0016, REG_W1, REG_0, BPF_REG_1,
offsetof(struct sk_buff, len));
/* s %w1,<data_len>(%b1) */
EMIT4_DISP(0x5b000000, REG_W1, BPF_REG_1,
offsetof(struct sk_buff, data_len));
/* stg %w1,ST_OFF_HLEN(%r0,%r15) */
EMIT6_DISP_LH(0xe3000000, 0x0024, REG_W1, REG_0, REG_15, STK_OFF_HLEN);
/* lg %skb_data,data_off(%b1) */
EMIT6_DISP_LH(0xe3000000, 0x0004, REG_SKB_DATA, REG_0,
BPF_REG_1, offsetof(struct sk_buff, data));
}

/*
* Emit function prologue
*
Expand Down Expand Up @@ -421,25 +442,12 @@ static void bpf_jit_prologue(struct bpf_jit *jit, bool is_classic)
EMIT6_DISP_LH(0xe3000000, 0x0024, REG_W1, REG_0,
REG_15, 152);
}
/*
* For SKB access %b1 contains the SKB pointer. For "bpf_jit.S"
* we store the SKB header length on the stack and the SKB data
* pointer in REG_SKB_DATA.
*/
if (jit->seen & SEEN_SKB) {
/* Header length: llgf %w1,<len>(%b1) */
EMIT6_DISP_LH(0xe3000000, 0x0016, REG_W1, REG_0, BPF_REG_1,
offsetof(struct sk_buff, len));
/* s %w1,<data_len>(%b1) */
EMIT4_DISP(0x5b000000, REG_W1, BPF_REG_1,
offsetof(struct sk_buff, data_len));
/* stg %w1,ST_OFF_HLEN(%r0,%r15) */
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, REG_W1, REG_0, REG_15,
STK_OFF_HLEN);
/* lg %skb_data,data_off(%b1) */
EMIT6_DISP_LH(0xe3000000, 0x0004, REG_SKB_DATA, REG_0,
BPF_REG_1, offsetof(struct sk_buff, data));
}
STK_OFF_SKBP);
/* Clear A (%b0) and X (%b7) registers for converted BPF programs */
if (is_classic) {
if (REG_SEEN(BPF_REG_A))
Expand Down Expand Up @@ -967,10 +975,6 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, int i
*/
const u64 func = (u64)__bpf_call_base + imm;

if (bpf_helper_changes_skb_data((void *)func))
/* TODO reload skb->data, hlen */
return -1;

REG_SET_SEEN(BPF_REG_5);
jit->seen |= SEEN_FUNC;
/* lg %w1,<d(imm)>(%l) */
Expand All @@ -980,6 +984,13 @@ 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_skb_data((void *)func)) {
jit->seen |= SEEN_SKB_CHANGE;
/* lg %b1,ST_OFF_SKBP(%r15) */
EMIT6_DISP_LH(0xe3000000, 0x0004, BPF_REG_1, REG_0,
REG_15, STK_OFF_SKBP);
emit_load_skb_data_hlen(jit);
}
break;
}
case BPF_JMP | BPF_CALL | BPF_X:
Expand Down

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