Re: [PATCH v8 1/8] sk_run_filter: add support for custom load_pointer

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On Thu, Feb 16, 2012 at 9:04 PM, Indan Zupancic <indan@xxxxxx> wrote:
> 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.

They are in the absolute.  Relatively, all performance improved with
my patch except for x86-nossp.

>> 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.

Making things run well on Atom is important for my daily work.  And it
usually means (barring Atom-specific weirdness) that it then runs even
better on bigger processors :)

>> v8: - fixed variable positioning and bad cast (eric.dumazet@xxxxxxxxx)
>>     - no longer passes A as a pointer (inspection of x86 asm shows A is
>>       %ebx again; thanks eric.dumazet@xxxxxxxxx)
>>     - cleaned up switch macros and expanded use
>>       (joe@xxxxxxxxxxx, indan@xxxxxx)
>>     - 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@xxxxxxxxxxxx>
>> ---
>>  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.

True, I'll rephrase.

>> + *   @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.

Fixed!

>>   */
>> -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.

That just means I need to disassemble after to make sure the compiler
does the right thing.  I'll do that and change it if gcc is doing the
right thing.

>>
>>               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.

I hope so.

>> +             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.

I'm changing it to constant length, but I can get rid of it
altogether. I don't care either way, it just depends on if there is
anyone else who will want this support.

>> +                     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.

I'm not sure that would make it any more readable though, especially
since I don't always break; after.

>> +             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,

Thanks!
will
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