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bpf: btf: Change how section is supported in btf_header
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There are currently unused section descriptions in the btf_header.  Those
sections are here to support future BTF use cases.  For example, the
func section (func_off) is to support function signature (e.g. the BPF
prog function signature).

Instead of spelling out all potential sections up-front in the btf_header.
This patch makes changes to btf_header such that extending it (e.g. adding
a section) is possible later.  The unused ones can be removed for now and
they can be added back later.

This patch:
1. adds a hdr_len to the btf_header.  It will allow adding
sections (and other info like parent_label and parent_name)
later.  The check is similar to the existing bpf_attr.
If a user passes in a longer hdr_len, the kernel
ensures the extra tailing bytes are 0.

2. allows the section order in the BTF object to be
different from its sec_off order in btf_header.

3. each sec_off is followed by a sec_len.  It must not have gap or
overlapping among sections.

The string section is ensured to be at the end due to the 4 bytes
alignment requirement of the type section.

The above changes will allow enough flexibility to
add new sections (and other info) to the btf_header later.

This patch also removes an unnecessary !err check
at the end of btf_parse().

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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Martin KaFai Lau authored and Daniel Borkmann committed May 23, 2018
1 parent dcab51f commit f80442a
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Showing 2 changed files with 160 additions and 57 deletions.
8 changes: 2 additions & 6 deletions include/uapi/linux/btf.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -12,15 +12,11 @@ struct btf_header {
__u16 magic;
__u8 version;
__u8 flags;

__u32 parent_label;
__u32 parent_name;
__u32 hdr_len;

/* All offsets are in bytes relative to the end of this header */
__u32 label_off; /* offset of label section */
__u32 object_off; /* offset of data object section*/
__u32 func_off; /* offset of function section */
__u32 type_off; /* offset of type section */
__u32 type_len; /* length of type section */
__u32 str_off; /* offset of string section */
__u32 str_len; /* length of string section */
};
Expand Down
209 changes: 158 additions & 51 deletions kernel/bpf/btf.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@
#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/idr.h>
#include <linux/sort.h>
#include <linux/bpf_verifier.h>
#include <linux/btf.h>

Expand Down Expand Up @@ -184,15 +185,13 @@ static DEFINE_IDR(btf_idr);
static DEFINE_SPINLOCK(btf_idr_lock);

struct btf {
union {
struct btf_header *hdr;
void *data;
};
void *data;
struct btf_type **types;
u32 *resolved_ids;
u32 *resolved_sizes;
const char *strings;
void *nohdr_data;
struct btf_header hdr;
u32 nr_types;
u32 types_size;
u32 data_size;
Expand Down Expand Up @@ -228,6 +227,11 @@ enum resolve_mode {

#define MAX_RESOLVE_DEPTH 32

struct btf_sec_info {
u32 off;
u32 len;
};

struct btf_verifier_env {
struct btf *btf;
u8 *visit_states;
Expand Down Expand Up @@ -418,14 +422,14 @@ static const struct btf_kind_operations *btf_type_ops(const struct btf_type *t)
static bool btf_name_offset_valid(const struct btf *btf, u32 offset)
{
return !BTF_STR_TBL_ELF_ID(offset) &&
BTF_STR_OFFSET(offset) < btf->hdr->str_len;
BTF_STR_OFFSET(offset) < btf->hdr.str_len;
}

static const char *btf_name_by_offset(const struct btf *btf, u32 offset)
{
if (!BTF_STR_OFFSET(offset))
return "(anon)";
else if (BTF_STR_OFFSET(offset) < btf->hdr->str_len)
else if (BTF_STR_OFFSET(offset) < btf->hdr.str_len)
return &btf->strings[BTF_STR_OFFSET(offset)];
else
return "(invalid-name-offset)";
Expand Down Expand Up @@ -536,7 +540,8 @@ static void btf_verifier_log_member(struct btf_verifier_env *env,
__btf_verifier_log(log, "\n");
}

static void btf_verifier_log_hdr(struct btf_verifier_env *env)
static void btf_verifier_log_hdr(struct btf_verifier_env *env,
u32 btf_data_size)
{
struct bpf_verifier_log *log = &env->log;
const struct btf *btf = env->btf;
Expand All @@ -545,19 +550,16 @@ static void btf_verifier_log_hdr(struct btf_verifier_env *env)
if (!bpf_verifier_log_needed(log))
return;

hdr = btf->hdr;
hdr = &btf->hdr;
__btf_verifier_log(log, "magic: 0x%x\n", hdr->magic);
__btf_verifier_log(log, "version: %u\n", hdr->version);
__btf_verifier_log(log, "flags: 0x%x\n", hdr->flags);
__btf_verifier_log(log, "parent_label: %u\n", hdr->parent_label);
__btf_verifier_log(log, "parent_name: %u\n", hdr->parent_name);
__btf_verifier_log(log, "label_off: %u\n", hdr->label_off);
__btf_verifier_log(log, "object_off: %u\n", hdr->object_off);
__btf_verifier_log(log, "func_off: %u\n", hdr->func_off);
__btf_verifier_log(log, "hdr_len: %u\n", hdr->hdr_len);
__btf_verifier_log(log, "type_off: %u\n", hdr->type_off);
__btf_verifier_log(log, "type_len: %u\n", hdr->type_len);
__btf_verifier_log(log, "str_off: %u\n", hdr->str_off);
__btf_verifier_log(log, "str_len: %u\n", hdr->str_len);
__btf_verifier_log(log, "btf_total_size: %u\n", btf->data_size);
__btf_verifier_log(log, "btf_total_size: %u\n", btf_data_size);
}

static int btf_add_type(struct btf_verifier_env *env, struct btf_type *t)
Expand Down Expand Up @@ -1754,9 +1756,9 @@ static int btf_check_all_metas(struct btf_verifier_env *env)
struct btf_header *hdr;
void *cur, *end;

hdr = btf->hdr;
hdr = &btf->hdr;
cur = btf->nohdr_data + hdr->type_off;
end = btf->nohdr_data + hdr->str_off;
end = btf->nohdr_data + hdr->type_len;

env->log_type_id = 1;
while (cur < end) {
Expand Down Expand Up @@ -1866,8 +1868,20 @@ static int btf_check_all_types(struct btf_verifier_env *env)

static int btf_parse_type_sec(struct btf_verifier_env *env)
{
const struct btf_header *hdr = &env->btf->hdr;
int err;

/* Type section must align to 4 bytes */
if (hdr->type_off & (sizeof(u32) - 1)) {
btf_verifier_log(env, "Unaligned type_off");
return -EINVAL;
}

if (!hdr->type_len) {
btf_verifier_log(env, "No type found");
return -EINVAL;
}

err = btf_check_all_metas(env);
if (err)
return err;
Expand All @@ -1881,10 +1895,15 @@ static int btf_parse_str_sec(struct btf_verifier_env *env)
struct btf *btf = env->btf;
const char *start, *end;

hdr = btf->hdr;
hdr = &btf->hdr;
start = btf->nohdr_data + hdr->str_off;
end = start + hdr->str_len;

if (end != btf->data + btf->data_size) {
btf_verifier_log(env, "String section is not at the end");
return -EINVAL;
}

if (!hdr->str_len || hdr->str_len - 1 > BTF_MAX_NAME_OFFSET ||
start[0] || end[-1]) {
btf_verifier_log(env, "Invalid string section");
Expand All @@ -1896,20 +1915,122 @@ static int btf_parse_str_sec(struct btf_verifier_env *env)
return 0;
}

static int btf_parse_hdr(struct btf_verifier_env *env)
static const size_t btf_sec_info_offset[] = {
offsetof(struct btf_header, type_off),
offsetof(struct btf_header, str_off),
};

static int btf_sec_info_cmp(const void *a, const void *b)
{
const struct btf_sec_info *x = a;
const struct btf_sec_info *y = b;

return (int)(x->off - y->off) ? : (int)(x->len - y->len);
}

static int btf_check_sec_info(struct btf_verifier_env *env,
u32 btf_data_size)
{
const unsigned int nr_secs = ARRAY_SIZE(btf_sec_info_offset);
struct btf_sec_info secs[nr_secs];
u32 total, expected_total, i;
const struct btf_header *hdr;
struct btf *btf = env->btf;
u32 meta_left;
const struct btf *btf;

btf = env->btf;
hdr = &btf->hdr;

if (btf->data_size < sizeof(*hdr)) {
/* Populate the secs from hdr */
for (i = 0; i < nr_secs; i++)
secs[i] = *(struct btf_sec_info *)((void *)hdr +
btf_sec_info_offset[i]);

sort(secs, nr_secs, sizeof(struct btf_sec_info),
btf_sec_info_cmp, NULL);

/* Check for gaps and overlap among sections */
total = 0;
expected_total = btf_data_size - hdr->hdr_len;
for (i = 0; i < nr_secs; i++) {
if (expected_total < secs[i].off) {
btf_verifier_log(env, "Invalid section offset");
return -EINVAL;
}
if (total < secs[i].off) {
/* gap */
btf_verifier_log(env, "Unsupported section found");
return -EINVAL;
}
if (total > secs[i].off) {
btf_verifier_log(env, "Section overlap found");
return -EINVAL;
}
if (expected_total - total < secs[i].len) {
btf_verifier_log(env,
"Total section length too long");
return -EINVAL;
}
total += secs[i].len;
}

/* There is data other than hdr and known sections */
if (expected_total != total) {
btf_verifier_log(env, "Unsupported section found");
return -EINVAL;
}

return 0;
}

static int btf_parse_hdr(struct btf_verifier_env *env, void __user *btf_data,
u32 btf_data_size)
{
const struct btf_header *hdr;
u32 hdr_len, hdr_copy;
/*
* Minimal part of the "struct btf_header" that
* contains the hdr_len.
*/
struct btf_min_header {
u16 magic;
u8 version;
u8 flags;
u32 hdr_len;
} __user *min_hdr;
struct btf *btf;
int err;

btf = env->btf;
min_hdr = btf_data;

if (btf_data_size < sizeof(*min_hdr)) {
btf_verifier_log(env, "hdr_len not found");
return -EINVAL;
}

if (get_user(hdr_len, &min_hdr->hdr_len))
return -EFAULT;

if (btf_data_size < hdr_len) {
btf_verifier_log(env, "btf_header not found");
return -EINVAL;
}

btf_verifier_log_hdr(env);
err = bpf_check_uarg_tail_zero(btf_data, sizeof(btf->hdr), hdr_len);
if (err) {
if (err == -E2BIG)
btf_verifier_log(env, "Unsupported btf_header");
return err;
}

hdr_copy = min_t(u32, hdr_len, sizeof(btf->hdr));
if (copy_from_user(&btf->hdr, btf_data, hdr_copy))
return -EFAULT;

hdr = &btf->hdr;

btf_verifier_log_hdr(env, btf_data_size);

hdr = btf->hdr;
if (hdr->magic != BTF_MAGIC) {
btf_verifier_log(env, "Invalid magic");
return -EINVAL;
Expand All @@ -1925,26 +2046,14 @@ static int btf_parse_hdr(struct btf_verifier_env *env)
return -ENOTSUPP;
}

meta_left = btf->data_size - sizeof(*hdr);
if (!meta_left) {
if (btf_data_size == hdr->hdr_len) {
btf_verifier_log(env, "No data");
return -EINVAL;
}

if (meta_left < hdr->type_off || hdr->str_off <= hdr->type_off ||
/* Type section must align to 4 bytes */
hdr->type_off & (sizeof(u32) - 1)) {
btf_verifier_log(env, "Invalid type_off");
return -EINVAL;
}

if (meta_left < hdr->str_off ||
meta_left - hdr->str_off < hdr->str_len) {
btf_verifier_log(env, "Invalid str_off or str_len");
return -EINVAL;
}

btf->nohdr_data = btf->hdr + 1;
err = btf_check_sec_info(env, btf_data_size);
if (err)
return err;

return 0;
}
Expand Down Expand Up @@ -1987,6 +2096,11 @@ static struct btf *btf_parse(void __user *btf_data, u32 btf_data_size,
err = -ENOMEM;
goto errout;
}
env->btf = btf;

err = btf_parse_hdr(env, btf_data, btf_data_size);
if (err)
goto errout;

data = kvmalloc(btf_data_size, GFP_KERNEL | __GFP_NOWARN);
if (!data) {
Expand All @@ -1996,18 +2110,13 @@ static struct btf *btf_parse(void __user *btf_data, u32 btf_data_size,

btf->data = data;
btf->data_size = btf_data_size;
btf->nohdr_data = btf->data + btf->hdr.hdr_len;

if (copy_from_user(data, btf_data, btf_data_size)) {
err = -EFAULT;
goto errout;
}

env->btf = btf;

err = btf_parse_hdr(env);
if (err)
goto errout;

err = btf_parse_str_sec(env);
if (err)
goto errout;
Expand All @@ -2016,16 +2125,14 @@ static struct btf *btf_parse(void __user *btf_data, u32 btf_data_size,
if (err)
goto errout;

if (!err && log->level && bpf_verifier_log_full(log)) {
if (log->level && bpf_verifier_log_full(log)) {
err = -ENOSPC;
goto errout;
}

if (!err) {
btf_verifier_env_free(env);
refcount_set(&btf->refcnt, 1);
return btf;
}
btf_verifier_env_free(env);
refcount_set(&btf->refcnt, 1);
return btf;

errout:
btf_verifier_env_free(env);
Expand Down

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