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SubjectRe: [PATCH v8 1/8] sk_run_filter: add support for custom load_pointer
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Hello,

On Thu, February 16, 2012 21:02, Will Drewry wrote:
> This change allows CONFIG_SECCOMP to make use of BPF programs for
> user-controlled system call filtering (as shown in this patch series).
>
> To minimize the impact on existing BPF evaluation, function pointer
> use must be declared at sk_chk_filter-time. This allows ancillary
> load instructions to be generated that use the function pointer rather
> than adding _any_ code to the existing LD_* instruction paths.
>
> Crude performance numbers using udpflood -l 10000000 against dummy0.
> 3 trials for baseline, 3 for with tcpdump. Averaged then differenced.
> Hard to believe trials were repeated at least a couple more times.
>
> * x86 32-bit (Atom N570 @ 1.66 GHz 2 core HT) [stackprot]:
> - Without: 94.05s - 76.36s = 17.68s
> - With: 86.22s - 73.30s = 12.92s
> - Slowdown per call: -476 nanoseconds
>
> * x86 32-bit (Atom N570 @ 1.66 GHz 2 core HT) [no stackprot]:
> - Without: 92.06s - 77.81s = 14.25s
> - With: 91.77s - 76.91s = 14.86s
> - Slowdown per call: +61 nanoseconds
>
> * x86 64-bit (Atom N570 @ 1.66 GHz 2 core HT) [stackprot]:
> - Without: 122.58s - 99.54s = 23.04s
> - With: 115.52s - 98.99s = 16.53s
> - Slowdown per call: -651 nanoseconds
>
> * x86 64-bit (Atom N570 @ 1.66 GHz 2 core HT) [no stackprot]:
> - Without: 114.95s - 91.92s = 23.03s
> - With: 110.47s - 90.79s = 19.68s
> - Slowdown per call: -335 nanoseconds
>
> This makes the x86-32-nossp make sense. Added register pressure always
> makes x86-32 sad.

Your 32-bit numbers are better than your 64-bit numbers, so I don't get
this comment.

> If this is a concern, I could change the call
> approach to bpf_run_filter to see if I can alleviate it a bit.
>
> That said, the x86-*-ssp numbers show a marked increase in performance.
> I've tested and retested and I keep getting these results. I'm also
> suprised by the nossp speed up on 64-bit, but I dunno. I haven't looked
> at the full disassembly of the call path. If that is required for the
> performance differences I'm seeing, please let me know. Or if I there is
> a preferred cpu to run this against - atoms can be a little weird.

Yeah, testing on Atom is a bit silly.

> v8: - fixed variable positioning and bad cast (eric.dumazet@gmail.com)
> - no longer passes A as a pointer (inspection of x86 asm shows A is
> %ebx again; thanks eric.dumazet@gmail.com)
> - cleaned up switch macros and expanded use
> (joe@perches.com, indan@nul.nu)
> - added length fn pointer and handled LD_W_LEN/LDX_W_LEN
> - moved from a wrapping struct to a typedef for the function
> pointer. (matches existing function pointer style)
> - added comprehensive comment above the typedef.
> - benchmarks
> v7: - first cut
>
> Signed-off-by: Will Drewry <wad@chromium.org>
> ---
> include/linux/filter.h | 69 +++++++++++++++++++++-
> net/core/filter.c | 152 +++++++++++++++++++++++++++++++++++++----------
> 2 files changed, 185 insertions(+), 36 deletions(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 8eeb205..d22ad46 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -110,6 +110,9 @@ struct sock_fprog { /* Required for SO_ATTACH_FILTER. */
> */
> #define BPF_MEMWORDS 16
>
> +/* BPF program (checking) flags */
> +#define BPF_CHK_FLAGS_NO_SKB 1
> +
> /* RATIONALE. Negative offsets are invalid in BPF.
> We use them to reference ancillary data.
> Unlike introduction new instructions, it does not break
> @@ -145,17 +148,67 @@ struct sk_filter
> struct sock_filter insns[0];
> };
>
> +/**
> + * struct bpf_load_fns - callbacks for bpf_run_filter
> + * These functions are called by bpf_run_filter if bpf_chk_filter
> + * was invoked with BPF_CHK_FLAGS_NO_SKB.
> + *
> + * pointer:
> + * @data: const pointer to the data passed into bpf_run_filter
> + * @k: offset into @skb's data
> + * @size: the size of the requested data in bytes: 1, 2, or 4.
> + * @buffer: If non-NULL, a 32-bit buffer for staging data.
> + *
> + * Returns a pointer to the requested data.
> + *
> + * This function operates similarly to load_pointer in net/core/filter.c
> + * except that the pointer to the returned data must already be
> + * byteswapped as appropriate to the source data and endianness.
> + * @buffer may be used if the data needs to be staged.
> + *
> + * length:
> + * @data: const pointer to the data passed into bpf_fun_filter
> + *
> + * Returns the length of the data.
> + */
> +struct bpf_load_fns {
> + void *(*pointer)(const void *data, int k, unsigned int size,
> + void *buffer);
> + u32 (*length)(const void *data);
> +};

Like I said in the other email, length is useless for the non-skb case.
If you really want to add it, just make it a constant. And 'pointer' isn't
the best name.

> +
> static inline unsigned int sk_filter_len(const struct sk_filter *fp)
> {
> return fp->len * sizeof(struct sock_filter) + sizeof(*fp);
> }
>
> +extern unsigned int bpf_run_filter(const void *data,
> + const struct sock_filter *filter,
> + const struct bpf_load_fns *load_fn);
> +
> +/**
> + * sk_run_filter - run a filter on a socket
> + * @skb: buffer to run the filter on
> + * @fentry: filter to apply
> + *
> + * Runs bpf_run_filter with the struct sk_buff-specific data
> + * accessor behavior.
> + */
> +static inline unsigned int sk_run_filter(const struct sk_buff *skb,
> + const struct sock_filter *filter)
> +{
> + return bpf_run_filter(skb, filter, NULL);
> +}
> +
> extern int sk_filter(struct sock *sk, struct sk_buff *skb);
> -extern unsigned int sk_run_filter(const struct sk_buff *skb,
> - const struct sock_filter *filter);
> extern int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk);
> extern int sk_detach_filter(struct sock *sk);
> -extern int sk_chk_filter(struct sock_filter *filter, unsigned int flen);
> +extern int bpf_chk_filter(struct sock_filter *filter, unsigned int flen, u32 flags);
> +
> +static inline int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
> +{
> + return bpf_chk_filter(filter, flen, 0);
> +}
>
> #ifdef CONFIG_BPF_JIT
> extern void bpf_jit_compile(struct sk_filter *fp);
> @@ -228,6 +281,16 @@ enum {
> BPF_S_ANC_HATYPE,
> BPF_S_ANC_RXHASH,
> BPF_S_ANC_CPU,
> + /* Used to differentiate SKB data and generic data */
> + BPF_S_ANC_LD_W_ABS,
> + BPF_S_ANC_LD_H_ABS,
> + BPF_S_ANC_LD_B_ABS,
> + BPF_S_ANC_LD_W_LEN,
> + BPF_S_ANC_LD_W_IND,
> + BPF_S_ANC_LD_H_IND,
> + BPF_S_ANC_LD_B_IND,
> + BPF_S_ANC_LDX_W_LEN,
> + BPF_S_ANC_LDX_B_MSH,
> };
>
> #endif /* __KERNEL__ */
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 5dea452..a5c98a9 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -98,9 +98,10 @@ int sk_filter(struct sock *sk, struct sk_buff *skb)
> EXPORT_SYMBOL(sk_filter);
>
> /**
> - * sk_run_filter - run a filter on a socket
> - * @skb: buffer to run the filter on
> + * bpf_run_filter - run a filter on a BPF program

The filter is the BPF program, so this comment is weird.

> + * @data: buffer to run the filter on
> * @fentry: filter to apply
> + * @load_fns: custom data accessor functions
> *
> * Decode and apply filter instructions to the skb->data.
> * Return length to keep, 0 for none. @skb is the data we are
> @@ -108,9 +109,13 @@ EXPORT_SYMBOL(sk_filter);
> * Because all jumps are guaranteed to be before last instruction,
> * and last instruction guaranteed to be a RET, we dont need to check
> * flen. (We used to pass to this function the length of filter)
> + *
> + * load_fn is only used if SKF_FLAGS_USE_LOAD_FNS was specified
> + * to sk_chk_generic_filter.

Stale comment.

> */
> -unsigned int sk_run_filter(const struct sk_buff *skb,
> - const struct sock_filter *fentry)
> +unsigned int bpf_run_filter(const void *data,
> + const struct sock_filter *fentry,
> + const struct bpf_load_fns *load_fns)
> {
> void *ptr;
> u32 A = 0; /* Accumulator */
> @@ -128,6 +133,7 @@ unsigned int sk_run_filter(const struct sk_buff *skb,
> #else
> const u32 K = fentry->k;
> #endif
> +#define SKB(_data) ((const struct sk_buff *)(_data))

Urgh!

If you had done:
const struct sk_buff *skb = data;

at the top, all those changed wouldn't be needed and it would look better too.

>
> switch (fentry->code) {
> case BPF_S_ALU_ADD_X:
> @@ -213,7 +219,7 @@ unsigned int sk_run_filter(const struct sk_buff *skb,
> case BPF_S_LD_W_ABS:
> k = K;
> load_w:
> - ptr = load_pointer(skb, k, 4, &tmp);
> + ptr = load_pointer(data, k, 4, &tmp);
> if (ptr != NULL) {
> A = get_unaligned_be32(ptr);
> continue;
> @@ -222,7 +228,7 @@ load_w:
> case BPF_S_LD_H_ABS:
> k = K;
> load_h:
> - ptr = load_pointer(skb, k, 2, &tmp);
> + ptr = load_pointer(data, k, 2, &tmp);
> if (ptr != NULL) {
> A = get_unaligned_be16(ptr);
> continue;
> @@ -231,17 +237,17 @@ load_h:
> case BPF_S_LD_B_ABS:
> k = K;
> load_b:
> - ptr = load_pointer(skb, k, 1, &tmp);
> + ptr = load_pointer(data, k, 1, &tmp);
> if (ptr != NULL) {
> A = *(u8 *)ptr;
> continue;
> }
> return 0;
> case BPF_S_LD_W_LEN:
> - A = skb->len;
> + A = SKB(data)->len;
> continue;
> case BPF_S_LDX_W_LEN:
> - X = skb->len;
> + X = SKB(data)->len;
> continue;
> case BPF_S_LD_W_IND:
> k = X + K;
> @@ -253,7 +259,7 @@ load_b:
> k = X + K;
> goto load_b;
> case BPF_S_LDX_B_MSH:
> - ptr = load_pointer(skb, K, 1, &tmp);
> + ptr = load_pointer(data, K, 1, &tmp);
> if (ptr != NULL) {
> X = (*(u8 *)ptr & 0xf) << 2;
> continue;
> @@ -288,29 +294,29 @@ load_b:
> mem[K] = X;
> continue;
> case BPF_S_ANC_PROTOCOL:
> - A = ntohs(skb->protocol);
> + A = ntohs(SKB(data)->protocol);
> continue;
> case BPF_S_ANC_PKTTYPE:
> - A = skb->pkt_type;
> + A = SKB(data)->pkt_type;
> continue;
> case BPF_S_ANC_IFINDEX:
> - if (!skb->dev)
> + if (!SKB(data)->dev)
> return 0;
> - A = skb->dev->ifindex;
> + A = SKB(data)->dev->ifindex;
> continue;
> case BPF_S_ANC_MARK:
> - A = skb->mark;
> + A = SKB(data)->mark;
> continue;
> case BPF_S_ANC_QUEUE:
> - A = skb->queue_mapping;
> + A = SKB(data)->queue_mapping;
> continue;
> case BPF_S_ANC_HATYPE:
> - if (!skb->dev)
> + if (!SKB(data)->dev)
> return 0;
> - A = skb->dev->type;
> + A = SKB(data)->dev->type;
> continue;
> case BPF_S_ANC_RXHASH:
> - A = skb->rxhash;
> + A = SKB(data)->rxhash;
> continue;
> case BPF_S_ANC_CPU:
> A = raw_smp_processor_id();
> @@ -318,15 +324,15 @@ load_b:
> case BPF_S_ANC_NLATTR: {
> struct nlattr *nla;
>
> - if (skb_is_nonlinear(skb))
> + if (skb_is_nonlinear(SKB(data)))
> return 0;
> - if (A > skb->len - sizeof(struct nlattr))
> + if (A > SKB(data)->len - sizeof(struct nlattr))
> return 0;
>
> - nla = nla_find((struct nlattr *)&skb->data[A],
> - skb->len - A, X);
> + nla = nla_find((struct nlattr *)&SKB(data)->data[A],
> + SKB(data)->len - A, X);
> if (nla)
> - A = (void *)nla - (void *)skb->data;
> + A = (void *)nla - (void *)SKB(data)->data;
> else
> A = 0;
> continue;
> @@ -334,22 +340,71 @@ load_b:
> case BPF_S_ANC_NLATTR_NEST: {
> struct nlattr *nla;
>
> - if (skb_is_nonlinear(skb))
> + if (skb_is_nonlinear(SKB(data)))
> return 0;
> - if (A > skb->len - sizeof(struct nlattr))
> + if (A > SKB(data)->len - sizeof(struct nlattr))
> return 0;
>
> - nla = (struct nlattr *)&skb->data[A];
> - if (nla->nla_len > A - skb->len)
> + nla = (struct nlattr *)&SKB(data)->data[A];
> + if (nla->nla_len > A - SKB(data)->len)
> return 0;
>
> nla = nla_find_nested(nla, X);
> if (nla)
> - A = (void *)nla - (void *)skb->data;
> + A = (void *)nla - (void *)SKB(data)->data;
> else
> A = 0;
> continue;
> }

All changes up to here are unnecessary.

> + case BPF_S_ANC_LD_W_ABS:
> + k = K;
> +load_fn_w:
> + ptr = load_fns->pointer(data, k, 4, &tmp);
> + if (ptr) {
> + A = *(u32 *)ptr;
> + continue;
> + }
> + return 0;
> + case BPF_S_ANC_LD_H_ABS:
> + k = K;
> +load_fn_h:
> + ptr = load_fns->pointer(data, k, 2, &tmp);
> + if (ptr) {
> + A = *(u16 *)ptr;
> + continue;
> + }
> + return 0;
> + case BPF_S_ANC_LD_B_ABS:
> + k = K;
> +load_fn_b:
> + ptr = load_fns->pointer(data, k, 1, &tmp);
> + if (ptr) {
> + A = *(u8 *)ptr;
> + continue;
> + }
> + return 0;
> + case BPF_S_ANC_LDX_B_MSH:
> + ptr = load_fns->pointer(data, K, 1, &tmp);
> + if (ptr) {
> + X = (*(u8 *)ptr & 0xf) << 2;
> + continue;
> + }
> + return 0;
> + case BPF_S_ANC_LD_W_IND:
> + k = X + K;
> + goto load_fn_w;
> + case BPF_S_ANC_LD_H_IND:
> + k = X + K;
> + goto load_fn_h;
> + case BPF_S_ANC_LD_B_IND:
> + k = X + K;
> + goto load_fn_b;
> + case BPF_S_ANC_LD_W_LEN:
> + A = load_fns->length(data);
> + continue;
> + case BPF_S_ANC_LDX_W_LEN:
> + X = load_fns->length(data);

These two should either return 0, be networking-only, just return 0/-1 or
use a constant length.

> + continue;
> default:
> WARN_RATELIMIT(1, "Unknown code:%u jt:%u tf:%u k:%u\n",
> fentry->code, fentry->jt,
> @@ -360,7 +415,7 @@ load_b:
>
> return 0;
> }
> -EXPORT_SYMBOL(sk_run_filter);
> +EXPORT_SYMBOL(bpf_run_filter);
>
> /*
> * Security :
> @@ -423,9 +478,10 @@ error:
> }
>
> /**
> - * sk_chk_filter - verify socket filter code
> + * bpf_chk_filter - verify socket filter BPF code
> * @filter: filter to verify
> * @flen: length of filter
> + * @flags: May be BPF_CHK_FLAGS_NO_SKB or 0
> *
> * Check the user's filter code. If we let some ugly
> * filter code slip through kaboom! The filter must contain
> @@ -434,9 +490,13 @@ error:
> *
> * All jumps are forward as they are not signed.
> *
> + * If BPF_CHK_FLAGS_NO_SKB is set in flags, any SKB-specific
> + * rules become illegal and a custom set of bpf_load_fns will
> + * be expected by bpf_run_filter.
> + *
> * Returns 0 if the rule set is legal or -EINVAL if not.
> */
> -int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
> +int bpf_chk_filter(struct sock_filter *filter, unsigned int flen, u32 flags)
> {
> /*
> * Valid instructions are initialized to non-0.
> @@ -542,9 +602,35 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
> pc + ftest->jf + 1 >= flen)
> return -EINVAL;
> break;
> +#define MAYBE_USE_LOAD_FN(CODE) \
> + if (flags & BPF_CHK_FLAGS_NO_SKB) { \
> + code = BPF_S_ANC_##CODE; \
> + break; \
> + }

You can as well hide everything in the macro then, including the case,
like the ANCILLARY() macro does.

> + case BPF_S_LD_W_LEN:
> + MAYBE_USE_LOAD_FN(LD_W_LEN);
> + break;
> + case BPF_S_LDX_W_LEN:
> + MAYBE_USE_LOAD_FN(LDX_W_LEN);
> + break;
> + case BPF_S_LD_W_IND:
> + MAYBE_USE_LOAD_FN(LD_W_IND);
> + break;
> + case BPF_S_LD_H_IND:
> + MAYBE_USE_LOAD_FN(LD_H_IND);
> + break;
> + case BPF_S_LD_B_IND:
> + MAYBE_USE_LOAD_FN(LD_B_IND);
> + break;
> + case BPF_S_LDX_B_MSH:
> + MAYBE_USE_LOAD_FN(LDX_B_MSH);
> + break;
> case BPF_S_LD_W_ABS:
> + MAYBE_USE_LOAD_FN(LD_W_ABS);
> case BPF_S_LD_H_ABS:
> + MAYBE_USE_LOAD_FN(LD_H_ABS);
> case BPF_S_LD_B_ABS:
> + MAYBE_USE_LOAD_FN(LD_B_ABS);
> #define ANCILLARY(CODE) case SKF_AD_OFF + SKF_AD_##CODE: \
> code = BPF_S_ANC_##CODE; \
> break
> @@ -572,7 +658,7 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
> }
> return -EINVAL;
> }
> -EXPORT_SYMBOL(sk_chk_filter);
> +EXPORT_SYMBOL(bpf_chk_filter);
>
> /**
> * sk_filter_release_rcu - Release a socket filter by rcu_head
> --
> 1.7.5.4
>

Greetings,

Indan




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