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SubjectRe: [REGRESSION][PATCH] bpf_jit drops the ball on indirect negative mem references
Date
Hi Jan,

On 30 Mar 2012, at 14:42, Jan Seiffert <kaffeemonster@googlemail.com> wrote:

> Eric Dumazet schrieb:
>> [snip]
>> All these ".p2align 1" are noise for this patch.
>>
>> This should be done as separate patch, explaining the rationale.
>>
>> ...
> Ok, i thought since you where concerned with the performance and
> I'm touching this stuff anyway.
> But you are right, can be done separately.
> So gone.
>
>> [snip]
>>
>> Please add the code for imm8 offsets as well ?
>>
>> if (is_imm8(K))
>> EMIT3(0x8d, 0x73, K); /* lea imm8(%rbx),%esi */
>> else
>> EMIT2_off32(0x8d, 0xb3, K); /* lea imm32(%rbx),%esi */
>
> Right, there is this imm8 form. I left it out because i never saw gas emit it
> and totally forgot about it.
> Your wish is my command. But since there is no EMIT2_off32 and introducing
> it would mean additional cleanup noise, i stayed with two emits.
>
> Do you know where i can ping the powerpc guys a little bit harder?

No need (unless you mean a different guy), I have enough guilt as it is! :) (Sorry for no response, am moving house and am netless.) I skimmed your patches on my phone but hope to be in a state to review/test over the weekend or early next week. :)


Cheers,

Matt


>
> So here a v3 of the patch:
>
> Consider the following test program:
>
> #include <stdio.h>
> #include <sys/types.h>
> #include <sys/socket.h>
> #include <netinet/in.h>
> #include <pcap-bpf.h>
>
> #define die(x) do {perror(x); return 1;} while (0)
> struct bpf_insn udp_filter[] = {
> /* 0 */ BPF_STMT(BPF_LDX|BPF_W|BPF_IMM, -1048576+(0)), /* leax net[0] */
> /* 1 */ BPF_STMT(BPF_LD|BPF_B|BPF_IND, 0), /* ldb [x+0] */
> /* 2 */ BPF_STMT(BPF_RET|BPF_A, 0), /* ret a */
> };
>
> int main(int argc, char *argv[])
> {
> char buf[512];
> struct sockaddr_in addr;
> struct bpf_program prg;
> socklen_t addr_s;
> ssize_t res;
> int fd;
>
> addr.sin_family = AF_INET;
> addr.sin_port = htons(5000);
> addr.sin_addr.s_addr = 0;
> addr_s = sizeof(addr);
> prg.bf_len = sizeof(udp_filter)/sizeof(udp_filter[0]);
> prg.bf_insns = udp_filter;
> if(-1 == (fd = socket(AF_INET, SOCK_DGRAM, 0)))
> die("socket");
> if(-1 == bind(fd, (struct sockaddr *)&addr, sizeof(addr)))
> die("bind");
> if(-1 == setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &prg, sizeof(prg)))
> die("setsockopt");
> res = recvfrom(fd, buf, sizeof(buf), 0, (struct sockaddr *)&addr, &addr_s);
> if(res != -1)
> printf("packet received: %zi bytes\n", res);
> else
> die("recvfrom");
> return 0;
> }
>
> when used with the bpf jit disabled works:
> console 1 $ ./bpf
> console 2 $ echo "hello" | nc -u localhost 5000
> console 1: packet received: 6 bytes
>
> When the bpf jit gets enabled (echo 100 >
> /proc/sys/net/core/bpf_jit_enable) the same program stops working:
> console 1 $ ./bpf
> console 2 $ echo "hello" | nc -u localhost 5000
> console 1:
>
> The reason is that both jits (x86 and powerpc) do not handle negative
> memory references like SKF_NET_OFF or SKF_LL_OFF, only the simple
> ancillary data references are supported (by mapping to special
> instructions).
> In the case of an absolute reference, the jit aborts the translation
> if a negative reference is seen, also a negative k on the indirect
> load aborts the translation, but if X is negative to begin with, only
> the error handler is reached at runtime which drops the whole packet.
>
> I propose the following patch to fix this situation.
> Lightly tested on x86, but the powerpc asm part is prop. wrong.
>
> Signed-of-by: Jan Seiffert <kaffeemonster@googlemail.com>
>
> diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
> index af1ab5e..e9b57b3 100644
> --- a/arch/powerpc/net/bpf_jit.h
> +++ b/arch/powerpc/net/bpf_jit.h
> @@ -49,6 +49,10 @@
> * Assembly helpers from arch/powerpc/net/bpf_jit.S:
> */
> extern u8 sk_load_word[], sk_load_half[], sk_load_byte[], sk_load_byte_msh[];
> +extern u8 sk_load_word_positive_offset[], sk_load_half_positive_offset[];
> +extern u8 sk_load_byte_positive_offset[], sk_load_byte_msh_positive_offset[];
> +extern u8 sk_load_word_negative_offset[], sk_load_half_negative_offset[];
> +extern u8 sk_load_byte_negative_offset[], sk_load_byte_msh_negative_offset[];
>
> #define FUNCTION_DESCR_SIZE 24
>
> diff --git a/arch/powerpc/net/bpf_jit_64.S b/arch/powerpc/net/bpf_jit_64.S
> index ff4506e..e590aa5 100644
> --- a/arch/powerpc/net/bpf_jit_64.S
> +++ b/arch/powerpc/net/bpf_jit_64.S
> @@ -31,14 +31,13 @@
> * then branch directly to slow_path_XXX if required. (In fact, could
> * load a spare GPR with the address of slow_path_generic and pass size
> * as an argument, making the call site a mtlr, li and bllr.)
> - *
> - * Technically, the "is addr < 0" check is unnecessary & slowing down
> - * the ABS path, as it's statically checked on generation.
> */
> .globl sk_load_word
> sk_load_word:
> cmpdi r_addr, 0
> - blt bpf_error
> + blt bpf_slow_path_word_neg
> + .globl sk_load_word_positive_offset
> +sk_load_word_positive_offset:
> /* Are we accessing past headlen? */
> subi r_scratch1, r_HL, 4
> cmpd r_scratch1, r_addr
> @@ -51,7 +50,9 @@ sk_load_word:
> .globl sk_load_half
> sk_load_half:
> cmpdi r_addr, 0
> - blt bpf_error
> + blt bpf_slow_path_half_neg
> + .globl sk_load_half_positive_offset
> +sk_load_half_positive_offset:
> subi r_scratch1, r_HL, 2
> cmpd r_scratch1, r_addr
> blt bpf_slow_path_half
> @@ -61,7 +62,9 @@ sk_load_half:
> .globl sk_load_byte
> sk_load_byte:
> cmpdi r_addr, 0
> - blt bpf_error
> + blt bpf_slow_path_byte_neg
> + .globl sk_load_byte_positive_offset
> +sk_load_byte_positive_offset:
> cmpd r_HL, r_addr
> ble bpf_slow_path_byte
> lbzx r_A, r_D, r_addr
> @@ -69,22 +72,20 @@ sk_load_byte:
>
> /*
> * BPF_S_LDX_B_MSH: ldxb 4*([offset]&0xf)
> - * r_addr is the offset value, already known positive
> + * r_addr is the offset value
> */
> .globl sk_load_byte_msh
> sk_load_byte_msh:
> + cmpdi r_addr, 0
> + blt bpf_slow_path_byte_msh_neg
> + .globl sk_load_byte_msh_positive_offset
> +sk_load_byte_msh_positive_offset:
> cmpd r_HL, r_addr
> ble bpf_slow_path_byte_msh
> lbzx r_X, r_D, r_addr
> rlwinm r_X, r_X, 2, 32-4-2, 31-2
> blr
>
> -bpf_error:
> - /* Entered with cr0 = lt */
> - li r3, 0
> - /* Generated code will 'blt epilogue', returning 0. */
> - blr
> -
> /* Call out to skb_copy_bits:
> * We'll need to back up our volatile regs first; we have
> * local variable space at r1+(BPF_PPC_STACK_BASIC).
> @@ -136,3 +137,85 @@ bpf_slow_path_byte_msh:
> lbz r_X, BPF_PPC_STACK_BASIC+(2*8)(r1)
> rlwinm r_X, r_X, 2, 32-4-2, 31-2
> blr
> +
> +/* Call out to bpf_internal_load_pointer_neg_helper:
> + * We'll need to back up our volatile regs first; we have
> + * local variable space at r1+(BPF_PPC_STACK_BASIC).
> + * Allocate a new stack frame here to remain ABI-compliant in
> + * stashing LR.
> + */
> +#define sk_negative_common(SIZE) \
> + mflr r0; \
> + std r0, 16(r1); \
> + /* R3 goes in parameter space of caller's frame */ \
> + std r_skb, (BPF_PPC_STACKFRAME+48)(r1); \
> + std r_A, (BPF_PPC_STACK_BASIC+(0*8))(r1); \
> + std r_X, (BPF_PPC_STACK_BASIC+(1*8))(r1); \
> + stdu r1, -BPF_PPC_SLOWPATH_FRAME(r1); \
> + /* R3 = r_skb, as passed */ \
> + mr r4, r_addr; \
> + li r5, SIZE; \
> + bl bpf_internal_load_pointer_neg_helper; \
> + /* R3 != 0 on success */ \
> + addi r1, r1, BPF_PPC_SLOWPATH_FRAME; \
> + ld r0, 16(r1); \
> + ld r_A, (BPF_PPC_STACK_BASIC+(0*8))(r1); \
> + ld r_X, (BPF_PPC_STACK_BASIC+(1*8))(r1); \
> + mtlr r0; \
> + cmpldi r3, 0; \
> + beq bpf_error_slow; /* cr0 = EQ */ \
> + mr r_addr, r3; \
> + ld r_skb, (BPF_PPC_STACKFRAME+48)(r1); \
> + /* Great success! */
> +
> +bpf_slow_path_word_neg:
> + lis r_scratch1,-32 /* SKF_LL_OFF */
> + cmpd r_addr, r_scratch1 /* addr < SKF_* */
> + blt bpf_error /* cr0 = LT */
> + .globl sk_load_word_negative_offset
> +sk_load_word_negative_offset:
> + sk_negative_common(4)
> + lwz r_A, 0(r_addr)
> + blr
> +
> +bpf_slow_path_half_neg:
> + lis r_scratch1,-32 /* SKF_LL_OFF */
> + cmpd r_addr, r_scratch1 /* addr < SKF_* */
> + blt bpf_error /* cr0 = LT */
> + .globl sk_load_half_negative_offset
> +sk_load_half_negative_offset:
> + sk_negative_common(2)
> + lhz r_A, 0(r_addr)
> + blr
> +
> +bpf_slow_path_byte_neg:
> + lis r_scratch1,-32 /* SKF_LL_OFF */
> + cmpd r_addr, r_scratch1 /* addr < SKF_* */
> + blt bpf_error /* cr0 = LT */
> + .globl sk_load_byte_negative_offset
> +sk_load_byte_negative_offset:
> + sk_negative_common(1)
> + lbz r_A, 0(r_addr)
> + blr
> +
> +bpf_slow_path_byte_msh_neg:
> + lis r_scratch1,-32 /* SKF_LL_OFF */
> + cmpd r_addr, r_scratch1 /* addr < SKF_* */
> + blt bpf_error /* cr0 = LT */
> + .globl sk_load_byte_msh_negative_offset
> +sk_load_byte_msh_negative_offset:
> + sk_negative_common(1)
> + lbz r_X, 0(r_addr)
> + rlwinm r_X, r_X, 2, 32-4-2, 31-2
> + blr
> +
> +bpf_error_slow:
> + /* fabricate a cr0 = lt */
> + li r_scratch1, -1
> + cmpdi r_scratch1, 0
> +bpf_error:
> + /* Entered with cr0 = lt */
> + li r3, 0
> + /* Generated code will 'blt epilogue', returning 0. */
> + blr
> +
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index 73619d3..2dc8b14 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -127,6 +127,9 @@ static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
> PPC_BLR();
> }
>
> +#define CHOOSE_LOAD_FUNC(K, func) \
> + ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset)
> +
> /* Assemble the body code between the prologue & epilogue. */
> static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
> struct codegen_context *ctx,
> @@ -391,21 +394,16 @@ static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
>
> /*** Absolute loads from packet header/data ***/
> case BPF_S_LD_W_ABS:
> - func = sk_load_word;
> + func = CHOOSE_LOAD_FUNC(K, sk_load_word);
> goto common_load;
> case BPF_S_LD_H_ABS:
> - func = sk_load_half;
> + func = CHOOSE_LOAD_FUNC(K, sk_load_half);
> goto common_load;
> case BPF_S_LD_B_ABS:
> - func = sk_load_byte;
> + func = CHOOSE_LOAD_FUNC(K, sk_load_byte);
> common_load:
> - /*
> - * Load from [K]. Reference with the (negative)
> - * SKF_NET_OFF/SKF_LL_OFF offsets is unsupported.
> - */
> + /* Load from [K]. */
> ctx->seen |= SEEN_DATAREF;
> - if ((int)K < 0)
> - return -ENOTSUPP;
> PPC_LI64(r_scratch1, func);
> PPC_MTLR(r_scratch1);
> PPC_LI32(r_addr, K);
> @@ -429,7 +427,7 @@ static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
> common_load_ind:
> /*
> * Load from [X + K]. Negative offsets are tested for
> - * in the helper functions, and result in a 'ret 0'.
> + * in the helper functions.
> */
> ctx->seen |= SEEN_DATAREF | SEEN_XREG;
> PPC_LI64(r_scratch1, func);
> @@ -443,13 +441,7 @@ static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
> break;
>
> case BPF_S_LDX_B_MSH:
> - /*
> - * x86 version drops packet (RET 0) when K<0, whereas
> - * interpreter does allow K<0 (__load_pointer, special
> - * ancillary data). common_load returns ENOTSUPP if K<0,
> - * so we fall back to interpreter & filter works.
> - */
> - func = sk_load_byte_msh;
> + func = CHOOSE_LOAD_FUNC(K, sk_load_byte_msh);
> goto common_load;
> break;
>
> diff --git a/arch/x86/net/bpf_jit.S b/arch/x86/net/bpf_jit.S
> index 6687022..2897d7f 100644
> --- a/arch/x86/net/bpf_jit.S
> +++ b/arch/x86/net/bpf_jit.S
> @@ -18,17 +18,17 @@
> * r9d : hlen = skb->len - skb->data_len
> */
> #define SKBDATA %r8
> -
> -sk_load_word_ind:
> - .globl sk_load_word_ind
> -
> - add %ebx,%esi /* offset += X */
> -# test %esi,%esi /* if (offset < 0) goto bpf_error; */
> - js bpf_error
> +#define SKF_MAX_NEG_OFF $(-0x200000) /* SKF_LL_OFF from filter.h */
>
> sk_load_word:
> .globl sk_load_word
>
> + test %esi,%esi
> + js bpf_slow_path_word_neg
> +
> +sk_load_word_positive_offset:
> + .globl sk_load_word_positive_offset
> +
> mov %r9d,%eax # hlen
> sub %esi,%eax # hlen - offset
> cmp $3,%eax
> @@ -37,16 +37,15 @@ sk_load_word:
> bswap %eax /* ntohl() */
> ret
>
> -
> -sk_load_half_ind:
> - .globl sk_load_half_ind
> -
> - add %ebx,%esi /* offset += X */
> - js bpf_error
> -
> sk_load_half:
> .globl sk_load_half
>
> + test %esi,%esi
> + js bpf_slow_path_half_neg
> +
> +sk_load_half_positive_offset:
> + .globl sk_load_half_positive_offset
> +
> mov %r9d,%eax
> sub %esi,%eax # hlen - offset
> cmp $1,%eax
> @@ -55,14 +54,15 @@ sk_load_half:
> rol $8,%ax # ntohs()
> ret
>
> -sk_load_byte_ind:
> - .globl sk_load_byte_ind
> - add %ebx,%esi /* offset += X */
> - js bpf_error
> -
> sk_load_byte:
> .globl sk_load_byte
>
> + test %esi,%esi
> + js bpf_slow_path_byte_neg
> +
> +sk_load_byte_positive_offset:
> + .globl sk_load_byte_positive_offset
> +
> cmp %esi,%r9d /* if (offset >= hlen) goto bpf_slow_path_byte */
> jle bpf_slow_path_byte
> movzbl (SKBDATA,%rsi),%eax
> @@ -73,25 +73,21 @@ sk_load_byte:
> *
> * Implements BPF_S_LDX_B_MSH : ldxb 4*([offset]&0xf)
> * Must preserve A accumulator (%eax)
> - * Inputs : %esi is the offset value, already known positive
> + * Inputs : %esi is the offset value
> */
> -ENTRY(sk_load_byte_msh)
> - CFI_STARTPROC
> +sk_load_byte_msh:
> + .globl sk_load_byte_msh
> + test %esi,%esi
> + js bpf_slow_path_byte_msh_neg
> +
> +sk_load_byte_msh_positive_offset:
> + .globl sk_load_byte_msh_positive_offset
> cmp %esi,%r9d /* if (offset >= hlen) goto bpf_slow_path_byte_msh */
> jle bpf_slow_path_byte_msh
> movzbl (SKBDATA,%rsi),%ebx
> and $15,%bl
> shl $2,%bl
> ret
> - CFI_ENDPROC
> -ENDPROC(sk_load_byte_msh)
> -
> -bpf_error:
> -# force a return 0 from jit handler
> - xor %eax,%eax
> - mov -8(%rbp),%rbx
> - leaveq
> - ret
>
> /* rsi contains offset and can be scratched */
> #define bpf_slow_path_common(LEN) \
> @@ -138,3 +134,68 @@ bpf_slow_path_byte_msh:
> shl $2,%al
> xchg %eax,%ebx
> ret
> +
> +#define sk_negative_common(SIZE) \
> + push %rdi; /* save skb */ \
> + push %r9; \
> + push SKBDATA; \
> +/* rsi already has offset */ \
> + mov $SIZE,%ecx; /* size */ \
> + call bpf_internal_load_pointer_neg_helper; \
> + test %rax,%rax; \
> + pop SKBDATA; \
> + pop %r9; \
> + pop %rdi; \
> + jz bpf_error
> +
> +
> +bpf_slow_path_word_neg:
> + cmp SKF_MAX_NEG_OFF, %esi /* test range */
> + jl bpf_error /* offset lower -> error */
> +sk_load_word_negative_offset:
> + .globl sk_load_word_negative_offset
> + sk_negative_common(4)
> + mov (%rax), %eax
> + bswap %eax
> + ret
> +
> +bpf_slow_path_half_neg:
> + cmp SKF_MAX_NEG_OFF, %esi
> + jl bpf_error
> +sk_load_half_negative_offset:
> + .globl sk_load_half_negative_offset
> + sk_negative_common(2)
> + mov (%rax),%ax
> + rol $8,%ax
> + movzwl %ax,%eax
> + ret
> +
> +bpf_slow_path_byte_neg:
> + cmp SKF_MAX_NEG_OFF, %esi
> + jl bpf_error
> +sk_load_byte_negative_offset:
> + .globl sk_load_byte_negative_offset
> + sk_negative_common(1)
> + movzbl (%rax), %eax
> + ret
> +
> +bpf_slow_path_byte_msh_neg:
> + cmp SKF_MAX_NEG_OFF, %esi
> + jl bpf_error
> +sk_load_byte_msh_negative_offset:
> + .globl sk_load_byte_msh_negative_offset
> + xchg %eax,%ebx /* dont lose A , X is about to be scratched */
> + sk_negative_common(1)
> + movzbl (%rax),%eax
> + and $15,%al
> + shl $2,%al
> + xchg %eax,%ebx
> + ret
> +
> +bpf_error:
> +# force a return 0 from jit handler
> + xor %eax,%eax
> + mov -8(%rbp),%rbx
> + leaveq
> + ret
> +
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 5671752..39a2e2c 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -30,7 +30,10 @@ int bpf_jit_enable __read_mostly;
> * assembly code in arch/x86/net/bpf_jit.S
> */
> extern u8 sk_load_word[], sk_load_half[], sk_load_byte[], sk_load_byte_msh[];
> -extern u8 sk_load_word_ind[], sk_load_half_ind[], sk_load_byte_ind[];
> +extern u8 sk_load_word_positive_offset[], sk_load_half_positive_offset[];
> +extern u8 sk_load_byte_positive_offset[], sk_load_byte_msh_positive_offset[];
> +extern u8 sk_load_word_negative_offset[], sk_load_half_negative_offset[];
> +extern u8 sk_load_byte_negative_offset[], sk_load_byte_msh_negative_offset[];
>
> static inline u8 *emit_code(u8 *ptr, u32 bytes, unsigned int len)
> {
> @@ -117,6 +120,8 @@ static inline void bpf_flush_icache(void *start, void *end)
> set_fs(old_fs);
> }
>
> +#define CHOOSE_LOAD_FUNC(K, func) \
> + ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset)
>
> void bpf_jit_compile(struct sk_filter *fp)
> {
> @@ -473,44 +478,46 @@ void bpf_jit_compile(struct sk_filter *fp)
> #endif
> break;
> case BPF_S_LD_W_ABS:
> - func = sk_load_word;
> + func = CHOOSE_LOAD_FUNC(K, sk_load_word);
> common_load: seen |= SEEN_DATAREF;
> - if ((int)K < 0) {
> - /* Abort the JIT because __load_pointer() is needed. */
> - goto out;
> - }
> t_offset = func - (image + addrs[i]);
> EMIT1_off32(0xbe, K); /* mov imm32,%esi */
> EMIT1_off32(0xe8, t_offset); /* call */
> break;
> case BPF_S_LD_H_ABS:
> - func = sk_load_half;
> + func = CHOOSE_LOAD_FUNC(K, sk_load_half);
> goto common_load;
> case BPF_S_LD_B_ABS:
> - func = sk_load_byte;
> + func = CHOOSE_LOAD_FUNC(K, sk_load_byte);
> goto common_load;
> case BPF_S_LDX_B_MSH:
> - if ((int)K < 0) {
> - /* Abort the JIT because __load_pointer() is needed. */
> - goto out;
> - }
> + func = CHOOSE_LOAD_FUNC(K, sk_load_byte_msh);
> seen |= SEEN_DATAREF | SEEN_XREG;
> - t_offset = sk_load_byte_msh - (image + addrs[i]);
> + t_offset = func - (image + addrs[i]);
> EMIT1_off32(0xbe, K); /* mov imm32,%esi */
> EMIT1_off32(0xe8, t_offset); /* call sk_load_byte_msh */
> break;
> case BPF_S_LD_W_IND:
> - func = sk_load_word_ind;
> + func = sk_load_word;
> common_load_ind: seen |= SEEN_DATAREF | SEEN_XREG;
> t_offset = func - (image + addrs[i]);
> - EMIT1_off32(0xbe, K); /* mov imm32,%esi */
> + if (K) {
> + if (is_imm8(K)) {
> + EMIT3(0x8d, 0x73, K); /* lea imm8(%rbx), %esi */
> + } else {
> + EMIT2(0x8d, 0xb3); /* lea imm32(%rbx),%esi */
> + EMIT(K, 4);
> + }
> + } else {
> + EMIT2(0x89,0xde); /* mov %ebx,%esi */
> + }
> EMIT1_off32(0xe8, t_offset); /* call sk_load_xxx_ind */
> break;
> case BPF_S_LD_H_IND:
> - func = sk_load_half_ind;
> + func = sk_load_half;
> goto common_load_ind;
> case BPF_S_LD_B_IND:
> - func = sk_load_byte_ind;
> + func = sk_load_byte;
> goto common_load_ind;
> case BPF_S_JMP_JA:
> t_offset = addrs[i + K] - addrs[i];
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 5dea452..04ca613 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -41,7 +41,7 @@
> #include <linux/ratelimit.h>
>
> /* No hurry in this branch */
> -static void *__load_pointer(const struct sk_buff *skb, int k, unsigned int size)
> +void *bpf_internal_load_pointer_neg_helper(const struct sk_buff *skb, int k, unsigned int size)
> {
> u8 *ptr = NULL;
>
> @@ -54,13 +54,14 @@ static void *__load_pointer(const struct sk_buff *skb, int k, unsigned int size)
> return ptr;
> return NULL;
> }
> +EXPORT_SYMBOL(bpf_internal_load_pointer_neg_helper);
>
> static inline void *load_pointer(const struct sk_buff *skb, int k,
> unsigned int size, void *buffer)
> {
> if (k >= 0)
> return skb_header_pointer(skb, k, size, buffer);
> - return __load_pointer(skb, k, size);
> + return bpf_internal_load_pointer_neg_helper(skb, k, size);
> }
>
> /**
>


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