diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 39ad3f54c..ceb095550 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1381,7 +1381,7 @@ static void restore_regs(const struct btf_func_model *m, u8 **prog, int nr_args, } static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog, - struct bpf_prog *p, int stack_size) + struct bpf_prog *p, int stack_size, bool mod_ret) { u8 *prog = *pprog; int cnt = 0; @@ -1402,6 +1402,13 @@ static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog, 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); @@ -1461,6 +1468,23 @@ static int emit_cond_near_jump(u8 **pprog, void *func, void *ip, u8 jmp_cond) 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) { @@ -1468,13 +1492,53 @@ static int invoke_bpf(const struct btf_func_model *m, u8 **pprog, u8 *prog = *pprog; for (i = 0; i < tp->nr_progs; i++) { - if (invoke_bpf_prog(m, &prog, tp->progs[i], stack_size)) + 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 @@ -1540,10 +1604,12 @@ 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 */ @@ -1576,24 +1642,60 @@ 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); @@ -1605,9 +1707,15 @@ 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_fallback_jump(u8 **pprog) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 1cc740ee1..071d3babf 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -466,6 +466,7 @@ 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/kernel/bpf/btf.c b/kernel/bpf/btf.c index 6ba465e25..c331408b5 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -3694,7 +3694,8 @@ 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 87340fd07..bec054190 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -1933,6 +1933,7 @@ 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 f8d8c2c2d..8f2273c4f 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -119,7 +119,8 @@ 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; err = arch_prepare_bpf_trampoline(new_image, new_image + PAGE_SIZE / 2, @@ -149,6 +150,8 @@ 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 880c87616..374fb1ef3 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10177,6 +10177,7 @@ 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)) {