From 3dd02da8234cc6c8b3dd5cd268ffeccee40270b1 Mon Sep 17 00:00:00 2001 From: KP Singh Date: Wed, 4 Mar 2020 20:18:49 +0100 Subject: [PATCH] BACKPORT: bpf: Introduce BPF_MODIFY_RETURN When multiple programs are attached, each program receives the return value from the previous program on the stack and the last program provides the return value to the attached function. The fmod_ret bpf programs are run after the fentry programs and before the fexit programs. The original function is only called if all the fmod_ret programs return 0 to avoid any unintended side-effects. The success value, i.e. 0 is not currently configurable but can be made so where user-space can specify it at load time. For example: int func_to_be_attached(int a, int b) { <--- do_fentry do_fmod_ret: if (ret != 0) goto do_fexit; original_function: } <--- do_fexit The fmod_ret program attached to this function can be defined as: SEC("fmod_ret/func_to_be_attached") int BPF_PROG(func_name, int a, int b, int ret) { // This will skip the original function logic. return 1; } The first fmod_ret program is passed 0 in its return argument. Change-Id: I87497d54c8da6278bf89dc9aed0d6453bd72ca29 Signed-off-by: KP Singh Signed-off-by: Alexei Starovoitov Acked-by: Andrii Nakryiko Acked-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20200304191853.1529-4-kpsingh@chromium.org --- arch/x86/net/bpf_jit_comp.c | 230 ++++++++++++++++++++++++++++----- include/linux/bpf.h | 1 + include/uapi/linux/bpf.h | 1 + kernel/bpf/btf.c | 3 +- kernel/bpf/syscall.c | 1 + kernel/bpf/trampoline.c | 5 +- kernel/bpf/verifier.c | 1 + tools/include/uapi/linux/bpf.h | 4 + 8 files changed, 213 insertions(+), 33 deletions(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 958edce1066b..d3850a6d8650 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1334,6 +1334,111 @@ static void restore_regs(const struct btf_func_model *m, u8 **prog, int nr_args, -(stack_size - i * 8)); } +static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog, + struct bpf_prog *p, int stack_size, bool mod_ret) +{ + u8 *prog = *pprog; + int cnt = 0; + + if (emit_call(&prog, __bpf_prog_enter, prog)) + return -EINVAL; + /* remember prog start time returned by __bpf_prog_enter */ + emit_mov_reg(&prog, true, BPF_REG_6, BPF_REG_0); + + /* arg1: lea rdi, [rbp - stack_size] */ + EMIT4(0x48, 0x8D, 0x7D, -stack_size); + /* arg2: progs[i]->insnsi for interpreter */ + if (!p->jited) + emit_mov_imm64(&prog, BPF_REG_2, + (long) p->insnsi >> 32, + (u32) (long) p->insnsi); + /* call JITed bpf program or interpreter */ + if (emit_call(&prog, p->bpf_func, prog)) + return -EINVAL; + + /* BPF_TRAMP_MODIFY_RETURN trampolines can modify the return + * of the previous call which is then passed on the stack to + * the next BPF program. + */ + if (mod_ret) + emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8); + + /* arg1: mov rdi, progs[i] */ + emit_mov_imm64(&prog, BPF_REG_1, (long) p >> 32, + (u32) (long) p); + /* arg2: mov rsi, rbx <- start time in nsec */ + emit_mov_reg(&prog, true, BPF_REG_2, BPF_REG_6); + if (emit_call(&prog, __bpf_prog_exit, prog)) + return -EINVAL; + + *pprog = prog; + return 0; +} + +static void emit_nops(u8 **pprog, unsigned int len) +{ + unsigned int i, noplen; + u8 *prog = *pprog; + int cnt = 0; + + while (len > 0) { + noplen = len; + + if (noplen > ASM_NOP_MAX) + noplen = ASM_NOP_MAX; + + for (i = 0; i < noplen; i++) + EMIT1(ideal_nops[noplen][i]); + len -= noplen; + } + + *pprog = prog; +} + +static void emit_align(u8 **pprog, u32 align) +{ + u8 *target, *prog = *pprog; + + target = PTR_ALIGN(prog, align); + if (target != prog) + emit_nops(&prog, target - prog); + + *pprog = prog; +} + +static int emit_cond_near_jump(u8 **pprog, void *func, void *ip, u8 jmp_cond) +{ + u8 *prog = *pprog; + int cnt = 0; + s64 offset; + + offset = func - (ip + 2 + 4); + if (!is_simm32(offset)) { + pr_err("Target %p is out of range\n", func); + return -EINVAL; + } + EMIT2_off32(0x0F, jmp_cond + 0x10, offset); + *pprog = prog; + return 0; +} + +static int emit_mod_ret_check_imm8(u8 **pprog, int value) +{ + u8 *prog = *pprog; + int cnt = 0; + + if (!is_imm8(value)) + return -EINVAL; + + if (value == 0) + EMIT2(0x85, add_2reg(0xC0, BPF_REG_0, BPF_REG_0)); + else + EMIT3(0x83, add_1reg(0xF8, BPF_REG_0), value); + + *pprog = prog; + return 0; +} + static int invoke_bpf(const struct btf_func_model *m, u8 **pprog, struct bpf_tramp_progs *tp, int stack_size) { @@ -1341,34 +1446,53 @@ static int invoke_bpf(const struct btf_func_model *m, u8 **pprog, int cnt = 0, i; for (i = 0; i < tp->nr_progs; i++) { - if (emit_call(&prog, __bpf_prog_enter, prog)) - return -EINVAL; - /* remember prog start time returned by __bpf_prog_enter */ - emit_mov_reg(&prog, true, BPF_REG_6, BPF_REG_0); - - /* arg1: lea rdi, [rbp - stack_size] */ - EMIT4(0x48, 0x8D, 0x7D, -stack_size); - /* arg2: progs[i]->insnsi for interpreter */ - if (!tp->progs[i]->jited) - emit_mov_imm64(&prog, BPF_REG_2, - (long) tp->progs[i]->insnsi >> 32, - (u32) (long) tp->progs[i]->insnsi); - /* call JITed bpf program or interpreter */ - if (emit_call(&prog, tp->progs[i]->bpf_func, prog)) - return -EINVAL; - - /* arg1: mov rdi, progs[i] */ - emit_mov_imm64(&prog, BPF_REG_1, (long) tp->progs[i] >> 32, - (u32) (long) tp->progs[i]); - /* arg2: mov rsi, rbx <- start time in nsec */ - emit_mov_reg(&prog, true, BPF_REG_2, BPF_REG_6); - if (emit_call(&prog, __bpf_prog_exit, prog)) + if (invoke_bpf_prog(m, &prog, tp->progs[i], stack_size, false)) return -EINVAL; } *pprog = prog; return 0; } +static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog, + struct bpf_tramp_progs *tp, int stack_size, + u8 **branches) +{ + u8 *prog = *pprog; + int i; + + /* The first fmod_ret program will receive a garbage return value. + * Set this to 0 to avoid confusing the program. + */ + emit_mov_imm32(&prog, false, BPF_REG_0, 0); + emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8); + for (i = 0; i < tp->nr_progs; i++) { + if (invoke_bpf_prog(m, &prog, tp->progs[i], stack_size, true)) + return -EINVAL; + + /* Generate a branch: + * + * if (ret != 0) + * goto do_fexit; + * + * If needed this can be extended to any integer value which can + * be passed by user-space when the program is loaded. + */ + if (emit_mod_ret_check_imm8(&prog, 0)) + return -EINVAL; + + /* Save the location of the branch and Generate 6 nops + * (4 bytes for an offset and 2 bytes for the jump) These nops + * are replaced with a conditional jump once do_fexit (i.e. the + * start of the fexit invocation) is finalized. + */ + branches[i] = prog; + emit_nops(&prog, 4 + 2); + } + + *pprog = prog; + return 0; +} + /* Example: * __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev); * its 'struct btf_func_model' will be nr_args=2 @@ -1434,10 +1558,12 @@ int arch_prepare_bpf_trampoline(void *image, void *image_end, struct bpf_tramp_progs *tprogs, void *orig_call) { - int cnt = 0, nr_args = m->nr_args; + int ret, i, cnt = 0, nr_args = m->nr_args; int stack_size = nr_args * 8; struct bpf_tramp_progs *fentry = &tprogs[BPF_TRAMP_FENTRY]; struct bpf_tramp_progs *fexit = &tprogs[BPF_TRAMP_FEXIT]; + struct bpf_tramp_progs *fmod_ret = &tprogs[BPF_TRAMP_MODIFY_RETURN]; + u8 **branches = NULL; u8 *prog; /* x86-64 supports up to 6 arguments. 7+ can be added in the future */ @@ -1470,24 +1596,60 @@ int arch_prepare_bpf_trampoline(void *image, void *image_end, if (invoke_bpf(m, &prog, fentry, stack_size)) return -EINVAL; + if (fmod_ret->nr_progs) { + branches = kcalloc(fmod_ret->nr_progs, sizeof(u8 *), + GFP_KERNEL); + if (!branches) + return -ENOMEM; + + if (invoke_bpf_mod_ret(m, &prog, fmod_ret, stack_size, + branches)) { + ret = -EINVAL; + goto cleanup; + } + } + if (flags & BPF_TRAMP_F_CALL_ORIG) { - if (fentry->nr_progs) + if (fentry->nr_progs || fmod_ret->nr_progs) restore_regs(m, &prog, nr_args, stack_size); /* call original function */ - if (emit_call(&prog, orig_call, prog)) - return -EINVAL; + if (emit_call(&prog, orig_call, prog)) { + ret = -EINVAL; + goto cleanup; + } /* remember return value in a stack for bpf prog to access */ emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8); } + if (fmod_ret->nr_progs) { + /* From Intel 64 and IA-32 Architectures Optimization + * Reference Manual, 3.4.1.4 Code Alignment, Assembly/Compiler + * Coding Rule 11: All branch targets should be 16-byte + * aligned. + */ + emit_align(&prog, 16); + /* Update the branches saved in invoke_bpf_mod_ret with the + * aligned address of do_fexit. + */ + for (i = 0; i < fmod_ret->nr_progs; i++) + emit_cond_near_jump(&branches[i], prog, branches[i], + X86_JNE); + } + if (fexit->nr_progs) - if (invoke_bpf(m, &prog, fexit, stack_size)) - return -EINVAL; + if (invoke_bpf(m, &prog, fexit, stack_size)) { + ret = -EINVAL; + goto cleanup; + } if (flags & BPF_TRAMP_F_RESTORE_REGS) restore_regs(m, &prog, nr_args, stack_size); + /* This needs to be done regardless. If there were fmod_ret programs, + * the return value is only updated on the stack and still needs to be + * restored to R0. + */ if (flags & BPF_TRAMP_F_CALL_ORIG) /* restore original return value back into RAX */ emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, -8); @@ -1499,9 +1661,15 @@ int arch_prepare_bpf_trampoline(void *image, void *image_end, EMIT4(0x48, 0x83, 0xC4, 8); /* add rsp, 8 */ EMIT1(0xC3); /* ret */ /* Make sure the trampoline generation logic doesn't overflow */ - if (WARN_ON_ONCE(prog > (u8 *)image_end - BPF_INSN_SAFETY)) - return -EFAULT; - return prog - (u8 *)image; + if (WARN_ON_ONCE(prog > (u8 *)image_end - BPF_INSN_SAFETY)) { + ret = -EFAULT; + goto cleanup; + } + ret = prog - (u8 *)image; + +cleanup: + kfree(branches); + return ret; } static int emit_cond_near_jump(u8 **pprog, void *func, void *ip, u8 jmp_cond) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 4309e5b330ee..dc9442777f6f 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -474,6 +474,7 @@ void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start); enum bpf_tramp_prog_type { BPF_TRAMP_FENTRY, BPF_TRAMP_FEXIT, + BPF_TRAMP_MODIFY_RETURN, BPF_TRAMP_MAX, BPF_TRAMP_REPLACE, /* more than MAX */ }; diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 1d58137caf46..8b655245ca09 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -210,6 +210,7 @@ enum bpf_attach_type { BPF_TRACE_RAW_TP, BPF_TRACE_FENTRY, BPF_TRACE_FEXIT, + BPF_MODIFY_RETURN, __MAX_BPF_ATTACH_TYPE }; diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index b50c21966c5c..df5415f0c6a9 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -3716,7 +3716,8 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, nr_args--; } - if (prog->expected_attach_type == BPF_TRACE_FEXIT && + if ((prog->expected_attach_type == BPF_TRACE_FEXIT || + prog->expected_attach_type == BPF_MODIFY_RETURN) && arg == nr_args) { if (!t) /* Default prog with 5 args. 6th arg is retval. */ diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 7487f1f27d8c..10b82a99abab 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -2327,6 +2327,7 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog) if (prog->expected_attach_type != BPF_TRACE_FENTRY && prog->expected_attach_type != BPF_TRACE_FEXIT && + prog->expected_attach_type != BPF_MODIFY_RETURN && prog->type != BPF_PROG_TYPE_EXT) { err = -EINVAL; goto out_put_prog; diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index 546198f6f307..221a17af1f81 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -232,7 +232,8 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr) goto out; } - if (tprogs[BPF_TRAMP_FEXIT].nr_progs) + if (tprogs[BPF_TRAMP_FEXIT].nr_progs || + tprogs[BPF_TRAMP_MODIFY_RETURN].nr_progs) flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME; /* Though the second half of trampoline page is unused a task could be @@ -269,6 +270,8 @@ static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(enum bpf_attach_type t) switch (t) { case BPF_TRACE_FENTRY: return BPF_TRAMP_FENTRY; + case BPF_MODIFY_RETURN: + return BPF_TRAMP_MODIFY_RETURN; case BPF_TRACE_FEXIT: return BPF_TRAMP_FEXIT; default: diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ff15efc844df..6980ea555024 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10218,6 +10218,7 @@ static int check_attach_btf_id(struct bpf_verifier_env *env) if (!prog_extension) return -EINVAL; /* fallthrough */ + case BPF_MODIFY_RETURN: case BPF_TRACE_FENTRY: case BPF_TRACE_FEXIT: if (!btf_type_is_func(t)) { diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index eb21dca33f0f..e1f9b3430980 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -199,6 +199,10 @@ enum bpf_attach_type { BPF_CGROUP_UDP6_RECVMSG, BPF_CGROUP_GETSOCKOPT, BPF_CGROUP_SETSOCKOPT, + BPF_TRACE_RAW_TP, + BPF_TRACE_FENTRY, + BPF_TRACE_FEXIT, + BPF_MODIFY_RETURN, __MAX_BPF_ATTACH_TYPE };