Messages in this thread Patch in this message | | | Date | Thu, 29 Mar 2012 13:54:00 +0200 | From | Jan Seiffert <> | Subject | Re: [REGRESSION][PATCH] bpf_jit drops the ball on indirect negative mem references |
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Eric Dumazet schrieb: > On Wed, 2012-03-28 at 22:26 +0200, Jan Seiffert wrote: > [snip] >> Say you have a UDP socket, and you want to filter for bogus source >> addresses (drop already in kernel to save the context switch). >> To have only one bpf program for ipv4 and ipv6 (you have to checked >> the same bogus v4 addresses in mapped space), there is a point where >> it elegant to have a negative offset saved in the X register. > Cool, thats a valid use, thanks. > > > Problem is you slow down the jit in its normal use, for a very specific > use. > > Please rework your patch so that absolute loads of positive offsets > (known at compile time) dont have to test negative offsets at run time. > > You add two instructions per load, and thats not good. > > Something like : > > 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 > > ... > > > Ok, to keep the ball rolling here is a V2 with the changes you suggested:
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..63ae130 100644 --- a/arch/x86/net/bpf_jit.S +++ b/arch/x86/net/bpf_jit.S @@ -18,17 +18,18 @@ * r9d : hlen = skb->len - skb->data_len */ #define SKBDATA %r8 +#define SKF_MAX_NEG_OFF $(-0x200000) /* SKF_LL_OFF from filter.h */ -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 - + .p2align 1 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 +38,16 @@ sk_load_word: bswap %eax /* ntohl() */ ret - -sk_load_half_ind: - .globl sk_load_half_ind - - add %ebx,%esi /* offset += X */ - js bpf_error - + .p2align 1 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 +56,16 @@ 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 - + .p2align 1 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 +76,22 @@ 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 + .p2align 1 +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) \ @@ -108,6 +108,7 @@ bpf_error: pop %rdi + .p2align 1 bpf_slow_path_word: bpf_slow_path_common(4) js bpf_error @@ -115,6 +116,7 @@ bpf_slow_path_word: bswap %eax ret + .p2align 1 bpf_slow_path_half: bpf_slow_path_common(2) js bpf_error @@ -123,12 +125,14 @@ bpf_slow_path_half: movzwl %ax,%eax ret + .p2align 1 bpf_slow_path_byte: bpf_slow_path_common(1) js bpf_error movzbl -12(%rbp),%eax ret + .p2align 1 bpf_slow_path_byte_msh: xchg %eax,%ebx /* dont lose A , X is about to be scratched */ bpf_slow_path_common(1) @@ -138,3 +142,73 @@ 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 + + + .p2align 1 +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 + + .p2align 1 +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 + + .p2align 1 +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 + + .p2align 1 +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 + + .p2align 1 +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..c20374f 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 +478,42 @@ 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) { + 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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