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