From: Florent Revest revest@chromium.org
mainline inclusion from mainline-5.13-rc1 commit 7b15523a989b63927c2bb08e9b5b0bbc10b58bef category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I5EUVD CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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The implementation takes inspiration from the existing bpf_trace_printk helper but there are a few differences:
To allow for a large number of format-specifiers, parameters are provided in an array, like in bpf_seq_printf.
Because the output string takes two arguments and the array of parameters also takes two arguments, the format string needs to fit in one argument. Thankfully, ARG_PTR_TO_CONST_STR is guaranteed to point to a zero-terminated read-only map so we don't need a format string length arg.
Because the format-string is known at verification time, we also do a first pass of format string validation in the verifier logic. This makes debugging easier.
Signed-off-by: Florent Revest revest@chromium.org Signed-off-by: Alexei Starovoitov ast@kernel.org Acked-by: Andrii Nakryiko andrii@kernel.org Link: https://lore.kernel.org/bpf/20210419155243.1632274-4-revest@chromium.org (cherry picked from commit 7b15523a989b63927c2bb08e9b5b0bbc10b58bef) Signed-off-by: Wang Yufen wangyufen@huawei.com --- include/linux/bpf.h | 1 + include/uapi/linux/bpf.h | 28 +++++++++++++++++++ kernel/bpf/helpers.c | 50 ++++++++++++++++++++++++++++++++++ kernel/bpf/verifier.c | 41 ++++++++++++++++++++++++++++ kernel/trace/bpf_trace.c | 2 ++ tools/include/uapi/linux/bpf.h | 28 +++++++++++++++++++ 6 files changed, 150 insertions(+)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index ebe82de2b1e0..d21db1caa869 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -2039,6 +2039,7 @@ extern const struct bpf_func_proto bpf_skc_to_tcp_request_sock_proto; extern const struct bpf_func_proto bpf_skc_to_udp6_sock_proto; extern const struct bpf_func_proto bpf_copy_from_user_proto; extern const struct bpf_func_proto bpf_snprintf_btf_proto; +extern const struct bpf_func_proto bpf_snprintf_proto; extern const struct bpf_func_proto bpf_per_cpu_ptr_proto; extern const struct bpf_func_proto bpf_this_cpu_ptr_proto; extern const struct bpf_func_proto bpf_for_each_map_elem_proto; diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index a3a037dc4b06..34a270e03aab 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -3846,6 +3846,33 @@ union bpf_attr { * Return * The number of traversed map elements for success, **-EINVAL** for * invalid **flags**. + * + * long bpf_snprintf(char *str, u32 str_size, const char *fmt, u64 *data, u32 data_len) + * Description + * Outputs a string into the **str** buffer of size **str_size** + * based on a format string stored in a read-only map pointed by + * **fmt**. + * + * Each format specifier in **fmt** corresponds to one u64 element + * in the **data** array. For strings and pointers where pointees + * are accessed, only the pointer values are stored in the *data* + * array. The *data_len* is the size of *data* in bytes. + * + * Formats **%s** and **%p{i,I}{4,6}** require to read kernel + * memory. Reading kernel memory may fail due to either invalid + * address or valid address but requiring a major memory fault. If + * reading kernel memory fails, the string for **%s** will be an + * empty string, and the ip address for **%p{i,I}{4,6}** will be 0. + * Not returning error to bpf program is consistent with what + * **bpf_trace_printk**\ () does for now. + * + * Return + * The strictly positive length of the formatted string, including + * the trailing zero character. If the return value is greater than + * **str_size**, **str** contains a truncated string, guaranteed to + * be zero-terminated except when **str_size** is 0. + * + * Or **-EBUSY** if the per-CPU memory copy buffer is busy. */ #define __BPF_FUNC_MAPPER(FN) \ FN(unspec), \ @@ -4010,6 +4037,7 @@ union bpf_attr { FN(sched_entity_to_cgrpid), \ FN(sched_entity_belongs_to_cgrp), \ FN(for_each_map_elem), \ + FN(snprintf), \ /* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 8009d372be02..e49b4cb5f099 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -909,6 +909,54 @@ int bpf_printf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args, return err; }
+#define MAX_SNPRINTF_VARARGS 12 + +BPF_CALL_5(bpf_snprintf, char *, str, u32, str_size, char *, fmt, + const void *, data, u32, data_len) +{ + enum bpf_printf_mod_type mod[MAX_SNPRINTF_VARARGS]; + u64 args[MAX_SNPRINTF_VARARGS]; + int err, num_args; + + if (data_len % 8 || data_len > MAX_SNPRINTF_VARARGS * 8 || + (data_len && !data)) + return -EINVAL; + num_args = data_len / 8; + + /* ARG_PTR_TO_CONST_STR guarantees that fmt is zero-terminated so we + * can safely give an unbounded size. + */ + err = bpf_printf_prepare(fmt, UINT_MAX, data, args, mod, num_args); + if (err < 0) + return err; + + /* Maximumly we can have MAX_SNPRINTF_VARARGS parameters, just give + * all of them to snprintf(). + */ + err = snprintf(str, str_size, fmt, BPF_CAST_FMT_ARG(0, args, mod), + BPF_CAST_FMT_ARG(1, args, mod), BPF_CAST_FMT_ARG(2, args, mod), + BPF_CAST_FMT_ARG(3, args, mod), BPF_CAST_FMT_ARG(4, args, mod), + BPF_CAST_FMT_ARG(5, args, mod), BPF_CAST_FMT_ARG(6, args, mod), + BPF_CAST_FMT_ARG(7, args, mod), BPF_CAST_FMT_ARG(8, args, mod), + BPF_CAST_FMT_ARG(9, args, mod), BPF_CAST_FMT_ARG(10, args, mod), + BPF_CAST_FMT_ARG(11, args, mod)); + + bpf_printf_cleanup(); + + return err + 1; +} + +const struct bpf_func_proto bpf_snprintf_proto = { + .func = bpf_snprintf, + .gpl_only = true, + .ret_type = RET_INTEGER, + .arg1_type = ARG_PTR_TO_MEM_OR_NULL, + .arg2_type = ARG_CONST_SIZE_OR_ZERO, + .arg3_type = ARG_PTR_TO_CONST_STR, + .arg4_type = ARG_PTR_TO_MEM_OR_NULL, + .arg5_type = ARG_CONST_SIZE_OR_ZERO, +}; + const struct bpf_func_proto bpf_get_current_task_proto __weak; const struct bpf_func_proto bpf_probe_read_user_proto __weak; const struct bpf_func_proto bpf_probe_read_user_str_proto __weak; @@ -997,6 +1045,8 @@ bpf_base_func_proto(enum bpf_func_id func_id) NULL : &bpf_probe_read_kernel_str_proto; case BPF_FUNC_snprintf_btf: return &bpf_snprintf_btf_proto; + case BPF_FUNC_snprintf: + return &bpf_snprintf_proto; default: return NULL; } diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index fa21ed4691a5..fe9799326522 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5847,6 +5847,41 @@ static int check_reference_leak(struct bpf_verifier_env *env) return state->acquired_refs ? -EINVAL : 0; }
+static int check_bpf_snprintf_call(struct bpf_verifier_env *env, + struct bpf_reg_state *regs) +{ + struct bpf_reg_state *fmt_reg = ®s[BPF_REG_3]; + struct bpf_reg_state *data_len_reg = ®s[BPF_REG_5]; + struct bpf_map *fmt_map = fmt_reg->map_ptr; + int err, fmt_map_off, num_args; + u64 fmt_addr; + char *fmt; + + /* data must be an array of u64 */ + if (data_len_reg->var_off.value % 8) + return -EINVAL; + num_args = data_len_reg->var_off.value / 8; + + /* fmt being ARG_PTR_TO_CONST_STR guarantees that var_off is const + * and map_direct_value_addr is set. + */ + fmt_map_off = fmt_reg->off + fmt_reg->var_off.value; + err = fmt_map->ops->map_direct_value_addr(fmt_map, &fmt_addr, + fmt_map_off); + if (err) + return err; + fmt = (char *)(long)fmt_addr + fmt_map_off; + + /* We are also guaranteed that fmt+fmt_map_off is NULL terminated, we + * can focus on validating the format specifiers. + */ + err = bpf_printf_prepare(fmt, UINT_MAX, NULL, NULL, NULL, num_args); + if (err < 0) + verbose(env, "Invalid format string\n"); + + return err; +} + static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn, int *insn_idx_p) { @@ -5963,6 +5998,12 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn return -EINVAL; }
+ if (func_id == BPF_FUNC_snprintf) { + err = check_bpf_snprintf_call(env, regs); + if (err < 0) + return err; + } + /* reset caller saved regs */ for (i = 0; i < CALLER_SAVED_REGS; i++) { mark_reg_not_init(env, regs, caller_saved[i]); diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 3e98255e6ec5..c08a504573a3 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -1036,6 +1036,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) return &bpf_this_cpu_ptr_proto; case BPF_FUNC_for_each_map_elem: return &bpf_for_each_map_elem_proto; + case BPF_FUNC_snprintf: + return &bpf_snprintf_proto; default: return NULL; } diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index c4341de31361..43109332f946 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -4556,6 +4556,33 @@ union bpf_attr { * Return * The number of traversed map elements for success, **-EINVAL** for * invalid **flags**. + * + * long bpf_snprintf(char *str, u32 str_size, const char *fmt, u64 *data, u32 data_len) + * Description + * Outputs a string into the **str** buffer of size **str_size** + * based on a format string stored in a read-only map pointed by + * **fmt**. + * + * Each format specifier in **fmt** corresponds to one u64 element + * in the **data** array. For strings and pointers where pointees + * are accessed, only the pointer values are stored in the *data* + * array. The *data_len* is the size of *data* in bytes. + * + * Formats **%s** and **%p{i,I}{4,6}** require to read kernel + * memory. Reading kernel memory may fail due to either invalid + * address or valid address but requiring a major memory fault. If + * reading kernel memory fails, the string for **%s** will be an + * empty string, and the ip address for **%p{i,I}{4,6}** will be 0. + * Not returning error to bpf program is consistent with what + * **bpf_trace_printk**\ () does for now. + * + * Return + * The strictly positive length of the formatted string, including + * the trailing zero character. If the return value is greater than + * **str_size**, **str** contains a truncated string, guaranteed to + * be zero-terminated except when **str_size** is 0. + * + * Or **-EBUSY** if the per-CPU memory copy buffer is busy. */ #define __BPF_FUNC_MAPPER(FN) \ FN(unspec), \ @@ -4720,6 +4747,7 @@ union bpf_attr { FN(sched_entity_to_cgrpid), \ FN(sched_entity_belongs_to_cgrp), \ FN(for_each_map_elem), \ + FN(snprintf), \ /* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper