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Merge branch 'Implement formatted output helpers with bstr_printf' 

Florent Revest says:

====================

BPF's formatted output helpers are currently implemented with
snprintf-like functions which use variadic arguments. The types of all
arguments need to be known at compilation time. BPF_CAST_FMT_ARG casts
all arguments to the size they should be (known at runtime), but the C
type promotion rules cast them back to u64s. On 32 bit architectures,
this can cause misaligned va_lists and generate mangled output.

This series refactors these helpers to avoid variadic arguments. It uses
a "binary printf" instead, where arguments are passed in a buffer
constructed at runtime.
---
Changes in v2:
- Reworded the second patch's description to better describe how
  arguments get mangled on 32 bit architectures
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Alexei Starovoitov 2021-04-27 15:50:15 -07:00
parent 2551c2d19c 48cac3f4a9
commit 05eb3791a0
7 changed files with 136 additions and 131 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
fs/seq_file.c
View File

@ -412,6 +412,24 @@ void seq_printf(struct seq_file *m, const char *f, ...)
}
EXPORT_SYMBOL(seq_printf);
#ifdef CONFIG_BINARY_PRINTF
void seq_bprintf(struct seq_file *m, const char *f, const u32 *binary)
{
int len;
if (m->count < m->size) {
len = bstr_printf(m->buf + m->count, m->size - m->count, f,
binary);
if (m->count + len < m->size) {
m->count += len;
return;
}
}
seq_set_overflow(m);
}
EXPORT_SYMBOL(seq_bprintf);
#endif /* CONFIG_BINARY_PRINTF */
/**
* mangle_path - mangle and copy path to buffer beginning
* @s: buffer start

22
include/linux/bpf.h
View File

@ -2081,24 +2081,8 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
struct btf_id_set;
bool btf_id_set_contains(const struct btf_id_set *set, u32 id);
enum bpf_printf_mod_type {
BPF_PRINTF_INT,
BPF_PRINTF_LONG,
BPF_PRINTF_LONG_LONG,
};
/* Workaround for getting va_list handling working with different argument type
* combinations generically for 32 and 64 bit archs.
*/
#define BPF_CAST_FMT_ARG(arg_nb, args, mod) \
(mod[arg_nb] == BPF_PRINTF_LONG_LONG || \
(mod[arg_nb] == BPF_PRINTF_LONG && __BITS_PER_LONG == 64) \
? (u64)args[arg_nb] \
: (u32)args[arg_nb])
int bpf_printf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
u64 *final_args, enum bpf_printf_mod_type *mod,
u32 num_args);
void bpf_printf_cleanup(void);
int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
u32 **bin_buf, u32 num_args);
void bpf_bprintf_cleanup(void);
#endif /* _LINUX_BPF_H */

4
include/linux/seq_file.h
View File

@ -146,6 +146,10 @@ void *__seq_open_private(struct file *, const struct seq_operations *, int);
int seq_open_private(struct file *, const struct seq_operations *, int);
int seq_release_private(struct inode *, struct file *);
#ifdef CONFIG_BINARY_PRINTF
void seq_bprintf(struct seq_file *m, const char *f, const u32 *binary);
#endif
#define DEFINE_SEQ_ATTRIBUTE(__name) \
static int __name ## _open(struct inode *inode, struct file *file) \
{ \

1
init/Kconfig
View File

@ -1708,6 +1708,7 @@ config BPF_SYSCALL
select BPF
select IRQ_WORK
select TASKS_TRACE_RCU
select BINARY_PRINTF
select NET_SOCK_MSG if INET
default n
help

188
kernel/bpf/helpers.c
View File

@ -707,9 +707,6 @@ static int try_get_fmt_tmp_buf(char **tmp_buf)
struct bpf_printf_buf *bufs;
int used;
if (*tmp_buf)
return 0;
preempt_disable();
used = this_cpu_inc_return(bpf_printf_buf_used);
if (WARN_ON_ONCE(used > 1)) {
@ -723,7 +720,7 @@ static int try_get_fmt_tmp_buf(char **tmp_buf)
return 0;
}
void bpf_printf_cleanup(void)
void bpf_bprintf_cleanup(void)
{
if (this_cpu_read(bpf_printf_buf_used)) {
this_cpu_dec(bpf_printf_buf_used);
@ -732,43 +729,45 @@ void bpf_printf_cleanup(void)
}
/*
* bpf_parse_fmt_str - Generic pass on format strings for printf-like helpers
* bpf_bprintf_prepare - Generic pass on format strings for bprintf-like helpers
*
* Returns a negative value if fmt is an invalid format string or 0 otherwise.
*
* This can be used in two ways:
* - Format string verification only: when final_args and mod are NULL
* - Format string verification only: when bin_args is NULL
* - Arguments preparation: in addition to the above verification, it writes in
* final_args a copy of raw_args where pointers from BPF have been sanitized
* into pointers safe to use by snprintf. This also writes in the mod array
* the size requirement of each argument, usable by BPF_CAST_FMT_ARG for ex.
* bin_args a binary representation of arguments usable by bstr_printf where
* pointers from BPF have been sanitized.
*
* In argument preparation mode, if 0 is returned, safe temporary buffers are
* allocated and bpf_printf_cleanup should be called to free them after use.
* allocated and bpf_bprintf_cleanup should be called to free them after use.
*/
int bpf_printf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
u64 *final_args, enum bpf_printf_mod_type *mod,
u32 num_args)
int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
u32 **bin_args, u32 num_args)
{
char *unsafe_ptr = NULL, *tmp_buf = NULL, *fmt_end;
size_t tmp_buf_len = MAX_PRINTF_BUF_LEN;
int err, i, num_spec = 0, copy_size;
enum bpf_printf_mod_type cur_mod;
char *unsafe_ptr = NULL, *tmp_buf = NULL, *tmp_buf_end, *fmt_end;
size_t sizeof_cur_arg, sizeof_cur_ip;
int err, i, num_spec = 0;
u64 cur_arg;
char fmt_ptype;
if (!!final_args != !!mod)
return -EINVAL;
char fmt_ptype, cur_ip[16], ip_spec[] = "%pXX";
fmt_end = strnchr(fmt, fmt_size, 0);
if (!fmt_end)
return -EINVAL;
fmt_size = fmt_end - fmt;
if (bin_args) {
if (num_args && try_get_fmt_tmp_buf(&tmp_buf))
return -EBUSY;
tmp_buf_end = tmp_buf + MAX_PRINTF_BUF_LEN;
*bin_args = (u32 *)tmp_buf;
}
for (i = 0; i < fmt_size; i++) {
if ((!isprint(fmt[i]) && !isspace(fmt[i])) || !isascii(fmt[i])) {
err = -EINVAL;
goto cleanup;
goto out;
}
if (fmt[i] != '%')
@ -781,7 +780,7 @@ int bpf_printf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
if (num_spec >= num_args) {
err = -EINVAL;
goto cleanup;
goto out;
}
/* The string is zero-terminated so if fmt[i] != 0, we can
@ -800,7 +799,7 @@ int bpf_printf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
}
if (fmt[i] == 'p') {
cur_mod = BPF_PRINTF_LONG;
sizeof_cur_arg = sizeof(long);
if ((fmt[i + 1] == 'k' || fmt[i + 1] == 'u') &&
fmt[i + 2] == 's') {
@ -811,117 +810,140 @@ int bpf_printf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
if (fmt[i + 1] == 0 || isspace(fmt[i + 1]) ||
ispunct(fmt[i + 1]) || fmt[i + 1] == 'K' ||
fmt[i + 1] == 'x' || fmt[i + 1] == 'B' ||
fmt[i + 1] == 's' || fmt[i + 1] == 'S') {
fmt[i + 1] == 'x' || fmt[i + 1] == 's' ||
fmt[i + 1] == 'S') {
/* just kernel pointers */
if (final_args)
if (tmp_buf)
cur_arg = raw_args[num_spec];
goto fmt_next;
i++;
goto nocopy_fmt;
}
if (fmt[i + 1] == 'B') {
if (tmp_buf) {
err = snprintf(tmp_buf,
(tmp_buf_end - tmp_buf),
"%pB",
(void *)(long)raw_args[num_spec]);
tmp_buf += (err + 1);
}
i++;
num_spec++;
continue;
}
/* only support "%pI4", "%pi4", "%pI6" and "%pi6". */
if ((fmt[i + 1] != 'i' && fmt[i + 1] != 'I') ||
(fmt[i + 2] != '4' && fmt[i + 2] != '6')) {
err = -EINVAL;
goto cleanup;
}
i += 2;
if (!final_args)
goto fmt_next;
if (try_get_fmt_tmp_buf(&tmp_buf)) {
err = -EBUSY;
goto out;
}
copy_size = (fmt[i + 2] == '4') ? 4 : 16;
if (tmp_buf_len < copy_size) {
i += 2;
if (!tmp_buf)
goto nocopy_fmt;
sizeof_cur_ip = (fmt[i] == '4') ? 4 : 16;
if (tmp_buf_end - tmp_buf < sizeof_cur_ip) {
err = -ENOSPC;
goto cleanup;
goto out;
}
unsafe_ptr = (char *)(long)raw_args[num_spec];
err = copy_from_kernel_nofault(tmp_buf, unsafe_ptr,
copy_size);
err = copy_from_kernel_nofault(cur_ip, unsafe_ptr,
sizeof_cur_ip);
if (err < 0)
memset(tmp_buf, 0, copy_size);
cur_arg = (u64)(long)tmp_buf;
tmp_buf += copy_size;
tmp_buf_len -= copy_size;
memset(cur_ip, 0, sizeof_cur_ip);
goto fmt_next;
/* hack: bstr_printf expects IP addresses to be
* pre-formatted as strings, ironically, the easiest way
* to do that is to call snprintf.
*/
ip_spec[2] = fmt[i - 1];
ip_spec[3] = fmt[i];
err = snprintf(tmp_buf, tmp_buf_end - tmp_buf,
ip_spec, &cur_ip);
tmp_buf += err + 1;
num_spec++;
continue;
} else if (fmt[i] == 's') {
cur_mod = BPF_PRINTF_LONG;
fmt_ptype = fmt[i];
fmt_str:
if (fmt[i + 1] != 0 &&
!isspace(fmt[i + 1]) &&
!ispunct(fmt[i + 1])) {
err = -EINVAL;
goto cleanup;
}
if (!final_args)
goto fmt_next;
if (try_get_fmt_tmp_buf(&tmp_buf)) {
err = -EBUSY;
goto out;
}
if (!tmp_buf_len) {
if (!tmp_buf)
goto nocopy_fmt;
if (tmp_buf_end == tmp_buf) {
err = -ENOSPC;
goto cleanup;
goto out;
}
unsafe_ptr = (char *)(long)raw_args[num_spec];
err = bpf_trace_copy_string(tmp_buf, unsafe_ptr,
fmt_ptype, tmp_buf_len);
fmt_ptype,
tmp_buf_end - tmp_buf);
if (err < 0) {
tmp_buf[0] = '\0';
err = 1;
}
cur_arg = (u64)(long)tmp_buf;
tmp_buf += err;
tmp_buf_len -= err;
num_spec++;
goto fmt_next;
continue;
}
cur_mod = BPF_PRINTF_INT;
sizeof_cur_arg = sizeof(int);
if (fmt[i] == 'l') {
cur_mod = BPF_PRINTF_LONG;
sizeof_cur_arg = sizeof(long);
i++;
}
if (fmt[i] == 'l') {
cur_mod = BPF_PRINTF_LONG_LONG;
sizeof_cur_arg = sizeof(long long);
i++;
}
if (fmt[i] != 'i' && fmt[i] != 'd' && fmt[i] != 'u' &&
fmt[i] != 'x' && fmt[i] != 'X') {
err = -EINVAL;
goto cleanup;
goto out;
}
if (final_args)
if (tmp_buf)
cur_arg = raw_args[num_spec];
fmt_next:
if (final_args) {
mod[num_spec] = cur_mod;
final_args[num_spec] = cur_arg;
nocopy_fmt:
if (tmp_buf) {
tmp_buf = PTR_ALIGN(tmp_buf, sizeof(u32));
if (tmp_buf_end - tmp_buf < sizeof_cur_arg) {
err = -ENOSPC;
goto out;
}
if (sizeof_cur_arg == 8) {
*(u32 *)tmp_buf = *(u32 *)&cur_arg;
*(u32 *)(tmp_buf + 4) = *((u32 *)&cur_arg + 1);
} else {
*(u32 *)tmp_buf = (u32)(long)cur_arg;
}
tmp_buf += sizeof_cur_arg;
}
num_spec++;
}
err = 0;
cleanup:
if (err)
bpf_printf_cleanup();
out:
if (err)
bpf_bprintf_cleanup();
return err;
}
@ -930,9 +952,8 @@ out:
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;
u32 *bin_args;
if (data_len % 8 || data_len > MAX_SNPRINTF_VARARGS * 8 ||
(data_len && !data))
@ -942,22 +963,13 @@ BPF_CALL_5(bpf_snprintf, char *, str, u32, str_size, char *, fmt,
/* 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);
err = bpf_bprintf_prepare(fmt, UINT_MAX, data, &bin_args, 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));
err = bstr_printf(str, str_size, fmt, bin_args);
bpf_printf_cleanup();
bpf_bprintf_cleanup();
return err + 1;
}

2
kernel/bpf/verifier.c
View File

@ -5946,7 +5946,7 @@ static int check_bpf_snprintf_call(struct bpf_verifier_env *env,
/* 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);
err = bpf_bprintf_prepare(fmt, UINT_MAX, NULL, NULL, num_args);
if (err < 0)
verbose(env, "Invalid format string\n");

32
kernel/trace/bpf_trace.c
View File

@ -381,27 +381,23 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
u64, arg2, u64, arg3)
{
u64 args[MAX_TRACE_PRINTK_VARARGS] = { arg1, arg2, arg3 };
enum bpf_printf_mod_type mod[MAX_TRACE_PRINTK_VARARGS];
u32 *bin_args;
static char buf[BPF_TRACE_PRINTK_SIZE];
unsigned long flags;
int ret;
ret = bpf_printf_prepare(fmt, fmt_size, args, args, mod,
MAX_TRACE_PRINTK_VARARGS);
ret = bpf_bprintf_prepare(fmt, fmt_size, args, &bin_args,
MAX_TRACE_PRINTK_VARARGS);
if (ret < 0)
return ret;
raw_spin_lock_irqsave(&trace_printk_lock, flags);
ret = snprintf(buf, sizeof(buf), fmt, BPF_CAST_FMT_ARG(0, args, mod),
BPF_CAST_FMT_ARG(1, args, mod), BPF_CAST_FMT_ARG(2, args, mod));
/* snprintf() will not append null for zero-length strings */
if (ret == 0)
buf[0] = '\0';
ret = bstr_printf(buf, sizeof(buf), fmt, bin_args);
trace_bpf_trace_printk(buf);
raw_spin_unlock_irqrestore(&trace_printk_lock, flags);
bpf_printf_cleanup();
bpf_bprintf_cleanup();
return ret;
}
@ -435,31 +431,21 @@ const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,
const void *, data, u32, data_len)
{
enum bpf_printf_mod_type mod[MAX_SEQ_PRINTF_VARARGS];
u64 args[MAX_SEQ_PRINTF_VARARGS];
int err, num_args;
u32 *bin_args;
if (data_len & 7 || data_len > MAX_SEQ_PRINTF_VARARGS * 8 ||
(data_len && !data))
return -EINVAL;
num_args = data_len / 8;
err = bpf_printf_prepare(fmt, fmt_size, data, args, mod, num_args);
err = bpf_bprintf_prepare(fmt, fmt_size, data, &bin_args, num_args);
if (err < 0)
return err;
/* Maximumly we can have MAX_SEQ_PRINTF_VARARGS parameter, just give
* all of them to seq_printf().
*/
seq_printf(m, 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));
seq_bprintf(m, fmt, bin_args);
bpf_printf_cleanup();
bpf_bprintf_cleanup();
return seq_has_overflowed(m) ? -EOVERFLOW : 0;
}