From b0bb20353b09149fdf7eaa65b2701e0cdfb305fd Mon Sep 17 00:00:00 2001 From: Hou Tao Date: Tue, 14 Sep 2021 10:33:51 +0800 Subject: [PATCH] BACKPORT: bpf: Handle return value of BPF_PROG_TYPE_STRUCT_OPS prog [ Upstream commit 356ed64991c6847a0c4f2e8fa3b1133f7a14f1fc ] Currently if a function ptr in struct_ops has a return value, its caller will get a random return value from it, because the return value of related BPF_PROG_TYPE_STRUCT_OPS prog is just dropped. So adding a new flag BPF_TRAMP_F_RET_FENTRY_RET to tell bpf trampoline to save and return the return value of struct_ops prog if ret_size of the function ptr is greater than 0. Also restricting the flag to be used alone. Fixes: 85d33df357b6 ("bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS") Change-Id: I5c327165a27004635727e5fe2060f310fc6a05e4 Signed-off-by: Hou Tao Signed-off-by: Alexei Starovoitov Acked-by: Martin KaFai Lau Link: https://lore.kernel.org/bpf/20210914023351.3664499-1-houtao1@huawei.com Signed-off-by: Sasha Levin --- arch/x86/net/bpf_jit_comp.c | 61 +++++++++++++++++++++++++++++-------- include/linux/bpf.h | 2 ++ kernel/bpf/bpf_struct_ops.c | 7 +++-- 3 files changed, 55 insertions(+), 15 deletions(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 03ff1814f77a..a4f74e91b770 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1634,7 +1634,7 @@ 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, bool mod_ret) + struct bpf_prog *p, int stack_size, bool save_ret) { u8 *prog = *pprog; int cnt = 0; @@ -1660,11 +1660,15 @@ 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 + /* + * 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. + * + * BPF_TRAMP_FENTRY trampoline may need to return the return + * value of BPF_PROG_TYPE_STRUCT_OPS prog. */ - if (mod_ret) + if (save_ret) emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8); if (p->aux->sleepable) { @@ -1749,13 +1753,15 @@ static int emit_mod_ret_check_imm8(u8 **pprog, int value) } static int invoke_bpf(const struct btf_func_model *m, u8 **pprog, - struct bpf_tramp_progs *tp, int stack_size) + struct bpf_tramp_progs *tp, int stack_size, + bool save_ret) { u8 *prog = *pprog; int cnt = 0, i; for (i = 0; i < tp->nr_progs; i++) { - if (invoke_bpf_prog(m, &prog, tp->progs[i], stack_size, false)) + if (invoke_bpf_prog(m, &prog, tp->progs[i], stack_size, + save_ret)) return -EINVAL; } *pprog = prog; @@ -1802,6 +1808,23 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog, return 0; } +static bool is_valid_bpf_tramp_flags(unsigned int flags) +{ + if ((flags & BPF_TRAMP_F_RESTORE_REGS) && + (flags & BPF_TRAMP_F_SKIP_FRAME)) + return false; + + /* + * BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops, + * and it must be used alone. + */ + if ((flags & BPF_TRAMP_F_RET_FENTRY_RET) && + (flags & ~BPF_TRAMP_F_RET_FENTRY_RET)) + return false; + + return true; +} + /* Example: * __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev); * its 'struct btf_func_model' will be nr_args=2 @@ -1874,17 +1897,19 @@ int arch_prepare_bpf_trampoline(void *image, void *image_end, struct bpf_tramp_progs *fmod_ret = &tprogs[BPF_TRAMP_MODIFY_RETURN]; u8 **branches = NULL; u8 *prog; + bool save_ret; /* x86-64 supports up to 6 arguments. 7+ can be added in the future */ if (nr_args > 6) return -ENOTSUPP; - if ((flags & BPF_TRAMP_F_RESTORE_REGS) && - (flags & BPF_TRAMP_F_SKIP_FRAME)) + if (!is_valid_bpf_tramp_flags(flags)) return -EINVAL; - if (flags & BPF_TRAMP_F_CALL_ORIG) - stack_size += 8; /* room for return value of orig_call */ + /* room for return value of orig_call or fentry prog */ + save_ret = flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET); + if (save_ret) + stack_size += 8; if (flags & BPF_TRAMP_F_SKIP_FRAME) /* skip patched call instruction and point orig_call to actual @@ -1902,7 +1927,8 @@ int arch_prepare_bpf_trampoline(void *image, void *image_end, save_regs(m, &prog, nr_args, stack_size); if (fentry->nr_progs) - if (invoke_bpf(m, &prog, fentry, stack_size)) + if (invoke_bpf(m, &prog, fentry, stack_size, + flags & BPF_TRAMP_F_RET_FENTRY_RET)) return -EINVAL; if (fmod_ret->nr_progs) { @@ -1947,7 +1973,7 @@ int arch_prepare_bpf_trampoline(void *image, void *image_end, } if (fexit->nr_progs) - if (invoke_bpf(m, &prog, fexit, stack_size)) { + if (invoke_bpf(m, &prog, fexit, stack_size, false)) { ret = -EINVAL; goto cleanup; } @@ -1959,8 +1985,17 @@ int arch_prepare_bpf_trampoline(void *image, void *image_end, * 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 */ + if (flags & BPF_TRAMP_F_CALL_ORIG) { + im->ip_epilogue = prog; + /* arg1: mov rdi, im */ + emit_mov_imm64(&prog, BPF_REG_1, (long) im >> 32, (u32) (long) im); + if (emit_call(&prog, __bpf_tramp_exit, prog)) { + ret = -EINVAL; + goto cleanup; + } + } + /* restore return value of orig_call or fentry prog back into RAX */ + if (save_ret) emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, -8); EMIT1(0x5B); /* pop rbx */ diff --git a/include/linux/bpf.h b/include/linux/bpf.h index c6ddf7e5979c..4b69e4a83ace 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -528,6 +528,8 @@ struct btf_func_model { * programs only. Should not be used with normal calls and indirect calls. */ #define BPF_TRAMP_F_SKIP_FRAME BIT(2) +/* Return the return value of fentry prog. Only used by bpf_struct_ops. */ +#define BPF_TRAMP_F_RET_FENTRY_RET BIT(4) /* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50 * bytes on x86. Pick a number to fit into BPF_IMAGE_SIZE / 2 diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c index 4c3b543bb33b..dea199bca5f8 100644 --- a/kernel/bpf/bpf_struct_ops.c +++ b/kernel/bpf/bpf_struct_ops.c @@ -367,6 +367,7 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key, const struct btf_type *mtype, *ptype; struct bpf_prog *prog; u32 moff; + u32 flags; moff = btf_member_bit_offset(t, member) / 8; ptype = btf_type_resolve_ptr(btf_vmlinux, member->type, NULL); @@ -430,10 +431,12 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key, tprogs[BPF_TRAMP_FENTRY].progs[0] = prog; tprogs[BPF_TRAMP_FENTRY].nr_progs = 1; + flags = st_ops->func_models[i].ret_size > 0 ? + BPF_TRAMP_F_RET_FENTRY_RET : 0; err = arch_prepare_bpf_trampoline(image, st_map->image + PAGE_SIZE, - &st_ops->func_models[i], 0, - tprogs, NULL); + &st_ops->func_models[i], + flags, tprogs, NULL); if (err < 0) goto reset_unlock;