diff options
| -rw-r--r-- | Documentation/sysctl/net.txt | 11 | ||||
| -rw-r--r-- | include/linux/filter.h | 42 | ||||
| -rw-r--r-- | kernel/bpf/core.c | 203 | ||||
| -rw-r--r-- | net/Kconfig | 7 | ||||
| -rw-r--r-- | net/core/sysctl_net_core.c | 9 |
5 files changed, 270 insertions, 2 deletions
diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt index 809ab6efcc74..f0480f7ea740 100644 --- a/Documentation/sysctl/net.txt +++ b/Documentation/sysctl/net.txt @@ -43,6 +43,17 @@ Values : 1 - enable the JIT 2 - enable the JIT and ask the compiler to emit traces on kernel log. +bpf_jit_harden +-------------- + +This enables hardening for the Berkeley Packet Filter Just in Time compiler. +Supported are eBPF JIT backends. Enabling hardening trades off performance, +but can mitigate JIT spraying. +Values : + 0 - disable JIT hardening (default value) + 1 - enable JIT hardening for unprivileged users only + 2 - enable JIT hardening for all users + dev_weight -------------- diff --git a/include/linux/filter.h b/include/linux/filter.h index 891852cf7716..6fc31ef1da2d 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -13,6 +13,8 @@ #include <linux/printk.h> #include <linux/workqueue.h> #include <linux/sched.h> +#include <linux/capability.h> + #include <net/sch_generic.h> #include <asm/cacheflush.h> @@ -42,6 +44,15 @@ struct bpf_prog_aux; #define BPF_REG_X BPF_REG_7 #define BPF_REG_TMP BPF_REG_8 +/* Kernel hidden auxiliary/helper register for hardening step. + * Only used by eBPF JITs. It's nothing more than a temporary + * register that JITs use internally, only that here it's part + * of eBPF instructions that have been rewritten for blinding + * constants. See JIT pre-step in bpf_jit_blind_constants(). + */ +#define BPF_REG_AX MAX_BPF_REG +#define MAX_BPF_JIT_REG (MAX_BPF_REG + 1) + /* BPF program can access up to 512 bytes of stack space. */ #define MAX_BPF_STACK 512 @@ -501,6 +512,7 @@ struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off, #ifdef CONFIG_BPF_JIT extern int bpf_jit_enable; +extern int bpf_jit_harden; typedef void (*bpf_jit_fill_hole_t)(void *area, unsigned int size); @@ -513,6 +525,9 @@ void bpf_jit_binary_free(struct bpf_binary_header *hdr); void bpf_jit_compile(struct bpf_prog *fp); void bpf_jit_free(struct bpf_prog *fp); +struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *fp); +void bpf_jit_prog_release_other(struct bpf_prog *fp, struct bpf_prog *fp_other); + static inline void bpf_jit_dump(unsigned int flen, unsigned int proglen, u32 pass, void *image) { @@ -523,6 +538,33 @@ static inline void bpf_jit_dump(unsigned int flen, unsigned int proglen, print_hex_dump(KERN_ERR, "JIT code: ", DUMP_PREFIX_OFFSET, 16, 1, image, proglen, false); } + +static inline bool bpf_jit_is_ebpf(void) +{ +# ifdef CONFIG_HAVE_EBPF_JIT + return true; +# else + return false; +# endif +} + +static inline bool bpf_jit_blinding_enabled(void) +{ + /* These are the prerequisites, should someone ever have the + * idea to call blinding outside of them, we make sure to + * bail out. + */ + if (!bpf_jit_is_ebpf()) + return false; + if (!bpf_jit_enable) + return false; + if (!bpf_jit_harden) + return false; + if (bpf_jit_harden == 1 && capable(CAP_SYS_ADMIN)) + return false; + + return true; +} #else static inline void bpf_jit_compile(struct bpf_prog *fp) { diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 70f0821aca47..f1e8a0def99b 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -243,6 +243,209 @@ void bpf_jit_binary_free(struct bpf_binary_header *hdr) { module_memfree(hdr); } + +int bpf_jit_harden __read_mostly; + +static int bpf_jit_blind_insn(const struct bpf_insn *from, + const struct bpf_insn *aux, + struct bpf_insn *to_buff) +{ + struct bpf_insn *to = to_buff; + u32 imm_rnd = prandom_u32(); + s16 off; + + BUILD_BUG_ON(BPF_REG_AX + 1 != MAX_BPF_JIT_REG); + BUILD_BUG_ON(MAX_BPF_REG + 1 != MAX_BPF_JIT_REG); + + if (from->imm == 0 && + (from->code == (BPF_ALU | BPF_MOV | BPF_K) || + from->code == (BPF_ALU64 | BPF_MOV | BPF_K))) { + *to++ = BPF_ALU64_REG(BPF_XOR, from->dst_reg, from->dst_reg); + goto out; + } + + switch (from->code) { + case BPF_ALU | BPF_ADD | BPF_K: + case BPF_ALU | BPF_SUB | BPF_K: + case BPF_ALU | BPF_AND | BPF_K: + case BPF_ALU | BPF_OR | BPF_K: + case BPF_ALU | BPF_XOR | BPF_K: + case BPF_ALU | BPF_MUL | BPF_K: + case BPF_ALU | BPF_MOV | BPF_K: + case BPF_ALU | BPF_DIV | BPF_K: + case BPF_ALU | BPF_MOD | BPF_K: + *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm); + *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); + *to++ = BPF_ALU32_REG(from->code, from->dst_reg, BPF_REG_AX); + break; + + case BPF_ALU64 | BPF_ADD | BPF_K: + case BPF_ALU64 | BPF_SUB | BPF_K: + case BPF_ALU64 | BPF_AND | BPF_K: + case BPF_ALU64 | BPF_OR | BPF_K: + case BPF_ALU64 | BPF_XOR | BPF_K: + case BPF_ALU64 | BPF_MUL | BPF_K: + case BPF_ALU64 | BPF_MOV | BPF_K: + case BPF_ALU64 | BPF_DIV | BPF_K: + case BPF_ALU64 | BPF_MOD | BPF_K: + *to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm); + *to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); + *to++ = BPF_ALU64_REG(from->code, from->dst_reg, BPF_REG_AX); + break; + + case BPF_JMP | BPF_JEQ | BPF_K: + case BPF_JMP | BPF_JNE | BPF_K: + case BPF_JMP | BPF_JGT | BPF_K: + case BPF_JMP | BPF_JGE | BPF_K: + case BPF_JMP | BPF_JSGT | BPF_K: + case BPF_JMP | BPF_JSGE | BPF_K: + case BPF_JMP | BPF_JSET | BPF_K: + /* Accommodate for extra offset in case of a backjump. */ + off = from->off; + if (off < 0) + off -= 2; + *to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm); + *to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); + *to++ = BPF_JMP_REG(from->code, from->dst_reg, BPF_REG_AX, off); + break; + + case BPF_LD | BPF_ABS | BPF_W: + case BPF_LD | BPF_ABS | BPF_H: + case BPF_LD | BPF_ABS | BPF_B: + *to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm); + *to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); + *to++ = BPF_LD_IND(from->code, BPF_REG_AX, 0); + break; + + case BPF_LD | BPF_IND | BPF_W: + case BPF_LD | BPF_IND | BPF_H: + case BPF_LD | BPF_IND | BPF_B: + *to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm); + *to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); + *to++ = BPF_ALU32_REG(BPF_ADD, BPF_REG_AX, from->src_reg); + *to++ = BPF_LD_IND(from->code, BPF_REG_AX, 0); + break; + + case BPF_LD | BPF_IMM | BPF_DW: + *to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ aux[1].imm); + *to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); + *to++ = BPF_ALU64_IMM(BPF_LSH, BPF_REG_AX, 32); + *to++ = BPF_ALU64_REG(BPF_MOV, aux[0].dst_reg, BPF_REG_AX); + break; + case 0: /* Part 2 of BPF_LD | BPF_IMM | BPF_DW. */ + *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ aux[0].imm); + *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); + *to++ = BPF_ALU64_REG(BPF_OR, aux[0].dst_reg, BPF_REG_AX); + break; + + case BPF_ST | BPF_MEM | BPF_DW: + case BPF_ST | BPF_MEM | BPF_W: + case BPF_ST | BPF_MEM | BPF_H: + case BPF_ST | BPF_MEM | BPF_B: + *to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm); + *to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); + *to++ = BPF_STX_MEM(from->code, from->dst_reg, BPF_REG_AX, from->off); + break; + } +out: + return to - to_buff; +} + +static struct bpf_prog *bpf_prog_clone_create(struct bpf_prog *fp_other, + gfp_t gfp_extra_flags) +{ + gfp_t gfp_flags = GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO | + gfp_extra_flags; + struct bpf_prog *fp; + + fp = __vmalloc(fp_other->pages * PAGE_SIZE, gfp_flags, PAGE_KERNEL); + if (fp != NULL) { + kmemcheck_annotate_bitfield(fp, meta); + + /* aux->prog still points to the fp_other one, so + * when promoting the clone to the real program, + * this still needs to be adapted. + */ + memcpy(fp, fp_other, fp_other->pages * PAGE_SIZE); + } + + return fp; +} + +static void bpf_prog_clone_free(struct bpf_prog *fp) +{ + /* aux was stolen by the other clone, so we cannot free + * it from this path! It will be freed eventually by the + * other program on release. + * + * At this point, we don't need a deferred release since + * clone is guaranteed to not be locked. + */ + fp->aux = NULL; + __bpf_prog_free(fp); +} + +void bpf_jit_prog_release_other(struct bpf_prog *fp, struct bpf_prog *fp_other) +{ + /* We have to repoint aux->prog to self, as we don't + * know whether fp here is the clone or the original. + */ + fp->aux->prog = fp; + bpf_prog_clone_free(fp_other); +} + +struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog) +{ + struct bpf_insn insn_buff[16], aux[2]; + struct bpf_prog *clone, *tmp; + int insn_delta, insn_cnt; + struct bpf_insn *insn; + int i, rewritten; + + if (!bpf_jit_blinding_enabled()) + return prog; + + clone = bpf_prog_clone_create(prog, GFP_USER); + if (!clone) + return ERR_PTR(-ENOMEM); + + insn_cnt = clone->len; + insn = clone->insnsi; + + for (i = 0; i < insn_cnt; i++, insn++) { + /* We temporarily need to hold the original ld64 insn + * so that we can still access the first part in the + * second blinding run. + */ + if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW) && + insn[1].code == 0) + memcpy(aux, insn, sizeof(aux)); + + rewritten = bpf_jit_blind_insn(insn, aux, insn_buff); + if (!rewritten) + continue; + + tmp = bpf_patch_insn_single(clone, i, insn_buff, rewritten); + if (!tmp) { + /* Patching may have repointed aux->prog during + * realloc from the original one, so we need to + * fix it up here on error. + */ + bpf_jit_prog_release_other(prog, clone); + return ERR_PTR(-ENOMEM); + } + + clone = tmp; + insn_delta = rewritten - 1; + + /* Walk new program and skip insns we just inserted. */ + insn = clone->insnsi + i + insn_delta; + insn_cnt += insn_delta; + i += insn_delta; + } + + return clone; +} #endif /* CONFIG_BPF_JIT */ /* Base function for offset calculation. Needs to go into .text section, diff --git a/net/Kconfig b/net/Kconfig index f7148f24f114..ff40562a782c 100644 --- a/net/Kconfig +++ b/net/Kconfig @@ -295,8 +295,11 @@ config BPF_JIT Berkeley Packet Filter filtering capabilities are normally handled by an interpreter. This option allows kernel to generate a native code when filter is loaded in memory. This should speedup - packet sniffing (libpcap/tcpdump). Note : Admin should enable - this feature changing /proc/sys/net/core/bpf_jit_enable + packet sniffing (libpcap/tcpdump). + + Note, admin should enable this feature changing: + /proc/sys/net/core/bpf_jit_enable + /proc/sys/net/core/bpf_jit_harden (optional) config NET_FLOW_LIMIT bool diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c index a6beb7b6ae55..0df2aa652530 100644 --- a/net/core/sysctl_net_core.c +++ b/net/core/sysctl_net_core.c @@ -294,6 +294,15 @@ static struct ctl_table net_core_table[] = { .mode = 0644, .proc_handler = proc_dointvec }, +# ifdef CONFIG_HAVE_EBPF_JIT + { + .procname = "bpf_jit_harden", + .data = &bpf_jit_harden, + .maxlen = sizeof(int), + .mode = 0600, + .proc_handler = proc_dointvec, + }, +# endif #endif { .procname = "netdev_tstamp_prequeue", |