linux.git/tools/lib/bpf/btf_dump.c, branch v6.7

libbpf: btf_dump_type_data_check_overflow needs to consider BTF_MEMBER_BITFIELD_SIZE

2023-05-01T13:37:38+00:00

The btf_dump/struct_data selftest is failing with:

  [...]
  test_btf_dump_struct_data:FAIL:unexpected return value dumping fs_context unexpected unexpected return value dumping fs_context: actual -7 != expected 264
  [...]

The reason is in btf_dump_type_data_check_overflow(). It does not use
BTF_MEMBER_BITFIELD_SIZE from the struct's member (btf_member). Instead,
it is using the enum size which is 4. It had been working till the recent
commit 4e04143c869c ("fs_context: drop the unused lsm_flags member")
removed an integer member which also removed the 4 bytes padding at the
end of the fs_context. Missing this 4 bytes padding exposed this bug. In
particular, when btf_dump_type_data_check_overflow() reaches the member
'phase', -E2BIG is returned.

The fix is to pass bit_sz to btf_dump_type_data_check_overflow(). In
btf_dump_type_data_check_overflow(), it does a different size check when
bit_sz is not zero.

The current fs_context:

[3600] ENUM 'fs_context_purpose' encoding=UNSIGNED size=4 vlen=3
	'FS_CONTEXT_FOR_MOUNT' val=0
	'FS_CONTEXT_FOR_SUBMOUNT' val=1
	'FS_CONTEXT_FOR_RECONFIGURE' val=2
[3601] ENUM 'fs_context_phase' encoding=UNSIGNED size=4 vlen=7
	'FS_CONTEXT_CREATE_PARAMS' val=0
	'FS_CONTEXT_CREATING' val=1
	'FS_CONTEXT_AWAITING_MOUNT' val=2
	'FS_CONTEXT_AWAITING_RECONF' val=3
	'FS_CONTEXT_RECONF_PARAMS' val=4
	'FS_CONTEXT_RECONFIGURING' val=5
	'FS_CONTEXT_FAILED' val=6
[3602] STRUCT 'fs_context' size=264 vlen=21
	'ops' type_id=3603 bits_offset=0
	'uapi_mutex' type_id=235 bits_offset=64
	'fs_type' type_id=872 bits_offset=1216
	'fs_private' type_id=21 bits_offset=1280
	'sget_key' type_id=21 bits_offset=1344
	'root' type_id=781 bits_offset=1408
	'user_ns' type_id=251 bits_offset=1472
	'net_ns' type_id=984 bits_offset=1536
	'cred' type_id=1785 bits_offset=1600
	'log' type_id=3621 bits_offset=1664
	'source' type_id=42 bits_offset=1792
	'security' type_id=21 bits_offset=1856
	's_fs_info' type_id=21 bits_offset=1920
	'sb_flags' type_id=20 bits_offset=1984
	'sb_flags_mask' type_id=20 bits_offset=2016
	's_iflags' type_id=20 bits_offset=2048
	'purpose' type_id=3600 bits_offset=2080 bitfield_size=8
	'phase' type_id=3601 bits_offset=2088 bitfield_size=8
	'need_free' type_id=67 bits_offset=2096 bitfield_size=1
	'global' type_id=67 bits_offset=2097 bitfield_size=1
	'oldapi' type_id=67 bits_offset=2098 bitfield_size=1

Fixes: 920d16af9b42 ("libbpf: BTF dumper support for typed data")
Signed-off-by: Martin KaFai Lau 
Signed-off-by: Daniel Borkmann 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/20230428013638.1581263-1-martin.lau@linux.dev

libbpf: Fix btf_dump's packed struct determination

2022-12-15T21:50:17+00:00

Fix bug in btf_dump's logic of determining if a given struct type is
packed or not. The notion of "natural alignment" is not needed and is
even harmful in this case, so drop it altogether. The biggest difference
in btf_is_struct_packed() compared to its original implementation is
that we don't really use btf__align_of() to determine overall alignment
of a struct type (because it could be 1 for both packed and non-packed
struct, depending on specifci field definitions), and just use field's
actual alignment to calculate whether any field is requiring packing or
struct's size overall necessitates packing.

Add two simple test cases that demonstrate the difference this change
would make.

Fixes: ea2ce1ba99aa ("libbpf: Fix BTF-to-C converter's padding logic")
Reported-by: Eduard Zingerman 
Signed-off-by: Andrii Nakryiko 
Signed-off-by: Daniel Borkmann 
Acked-by: Eduard Zingerman 
Link: https://lore.kernel.org/bpf/20221215183605.4149488-1-andrii@kernel.org

libbpf: Fix BTF-to-C converter's padding logic

2022-12-14T23:05:13+00:00

Turns out that btf_dump API doesn't handle a bunch of tricky corner
cases, as reported by Per, and further discovered using his testing
Python script ([0]).

This patch revamps btf_dump's padding logic significantly, making it
more correct and also avoiding unnecessary explicit padding, where
compiler would pad naturally. This overall topic turned out to be very
tricky and subtle, there are lots of subtle corner cases. The comments
in the code tries to give some clues, but comments themselves are
supposed to be paired with good understanding of C alignment and padding
rules. Plus some experimentation to figure out subtle things like
whether `long :0;` means that struct is now forced to be long-aligned
(no, it's not, turns out).

Anyways, Per's script, while not completely correct in some known
situations, doesn't show any obvious cases where this logic breaks, so
this is a nice improvement over the previous state of this logic.

Some selftests had to be adjusted to accommodate better use of natural
alignment rules, eliminating some unnecessary padding, or changing it to
`type: 0;` alignment markers.

Note also that for when we are in between bitfields, we emit explicit
bit size, while otherwise we use `: 0`, this feels much more natural in
practice.

Next patch will add few more test cases, found through randomized Per's
script.

[0] https://lore.kernel.org/bpf/85f83c333f5355c8ac026f835b18d15060725fcb.camel@ericsson.com/

Reported-by: Per Sundström XP
Signed-off-by: Andrii Nakryiko
Signed-off-by: Daniel Borkmann
Link: https://lore.kernel.org/bpf/20221212211505.558851-6-andrii@kernel.org

libbpf: Handle non-standardly sized enums better in BTF-to-C dumper

2022-12-14T23:05:12+00:00

Turns out C allows to force enum to be 1-byte or 8-byte explicitly using
mode(byte) or mode(word), respecticely. Linux sources are using this in
some cases. This is imporant to handle correctly, as enum size
determines corresponding fields in a struct that use that enum type. And
if enum size is incorrect, this will lead to invalid struct layout. So
add mode(byte) and mode(word) attribute support to btf_dump APIs.

Signed-off-by: Andrii Nakryiko 
Signed-off-by: Daniel Borkmann 
Link: https://lore.kernel.org/bpf/20221212211505.558851-3-andrii@kernel.org

libbpf: Fix single-line struct definition output in btf_dump

2022-12-14T23:05:12+00:00

btf_dump APIs emit unnecessary tabs when emitting struct/union
definition that fits on the single line. Before this patch we'd get:

struct blah {};

This patch fixes this and makes sure that we get more natural:

struct blah {};

Fixes: 44a726c3f23c ("bpftool: Print newline before '}' for struct with padding only fields")
Signed-off-by: Andrii Nakryiko 
Signed-off-by: Daniel Borkmann 
Link: https://lore.kernel.org/bpf/20221212211505.558851-2-andrii@kernel.org

libbpf: Ignore hashmap__find() result explicitly in btf_dump

2022-11-18T22:13:38+00:00

Coverity is reporting that btf_dump_name_dups() doesn't check return
result of hashmap__find() call. This is intentional, so make it explicit
with (void) cast.

Signed-off-by: Andrii Nakryiko 
Signed-off-by: Daniel Borkmann 
Link: https://lore.kernel.org/bpf/20221117192824.4093553-1-andrii@kernel.org

libbpf: Fix uninitialized warning in btf_dump_dump_type_data

2022-11-14T18:02:32+00:00

GCC 11.3.0 fails to compile btf_dump.c due to the following error,
which seems to originate in btf_dump_struct_data where the returned
value would be uninitialized if btf_vlen returns zero.

btf_dump.c: In function ‘btf_dump_dump_type_data’:
btf_dump.c:2363:12: error: ‘err’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
 2363 |         if (err < 0)
      |            ^

Fixes: 920d16af9b42 ("libbpf: BTF dumper support for typed data")
Signed-off-by: David Michael 
Signed-off-by: Daniel Borkmann 
Acked-by: Stanislav Fomichev 
Acked-by: Alan Maguire 
Link: https://lore.kernel.org/bpf/87zgcu60hq.fsf@gmail.com

libbpf: Hashmap interface update to allow both long and void* keys/values

2022-11-10T04:45:14+00:00

An update for libbpf's hashmap interface from void* -> void* to a
polymorphic one, allowing both long and void* keys and values.

This simplifies many use cases in libbpf as hashmaps there are mostly
integer to integer.

Perf copies hashmap implementation from libbpf and has to be
updated as well.

Changes to libbpf, selftests/bpf and perf are packed as a single
commit to avoid compilation issues with any future bisect.

Polymorphic interface is acheived by hiding hashmap interface
functions behind auxiliary macros that take care of necessary
type casts, for example:

    #define hashmap_cast_ptr(p)						\
	({								\
		_Static_assert((p) == NULL || sizeof(*(p)) == sizeof(long),\
			       #p " pointee should be a long-sized integer or a pointer"); \
		(long *)(p);						\
	})

    bool hashmap_find(const struct hashmap *map, long key, long *value);

    #define hashmap__find(map, key, value) \
		hashmap_find((map), (long)(key), hashmap_cast_ptr(value))

- hashmap__find macro casts key and value parameters to long
  and long* respectively
- hashmap_cast_ptr ensures that value pointer points to a memory
  of appropriate size.

This hack was suggested by Andrii Nakryiko in [1].
This is a follow up for [2].

[1] https://lore.kernel.org/bpf/CAEf4BzZ8KFneEJxFAaNCCFPGqp20hSpS2aCj76uRk3-qZUH5xg@mail.gmail.com/
[2] https://lore.kernel.org/bpf/af1facf9-7bc8-8a3d-0db4-7b3f333589a2@meta.com/T/#m65b28f1d6d969fcd318b556db6a3ad499a42607d

Signed-off-by: Eduard Zingerman 
Signed-off-by: Andrii Nakryiko 
Link: https://lore.kernel.org/bpf/20221109142611.879983-2-eddyz87@gmail.com

libbpf: Fix use-after-free in btf_dump_name_dups

2022-10-13T17:53:03+00:00

ASAN reports an use-after-free in btf_dump_name_dups:

ERROR: AddressSanitizer: heap-use-after-free on address 0xffff927006db at pc 0xaaaab5dfb618 bp 0xffffdd89b890 sp 0xffffdd89b928
READ of size 2 at 0xffff927006db thread T0
    #0 0xaaaab5dfb614 in __interceptor_strcmp.part.0 (test_progs+0x21b614)
    #1 0xaaaab635f144 in str_equal_fn tools/lib/bpf/btf_dump.c:127
    #2 0xaaaab635e3e0 in hashmap_find_entry tools/lib/bpf/hashmap.c:143
    #3 0xaaaab635e72c in hashmap__find tools/lib/bpf/hashmap.c:212
    #4 0xaaaab6362258 in btf_dump_name_dups tools/lib/bpf/btf_dump.c:1525
    #5 0xaaaab636240c in btf_dump_resolve_name tools/lib/bpf/btf_dump.c:1552
    #6 0xaaaab6362598 in btf_dump_type_name tools/lib/bpf/btf_dump.c:1567
    #7 0xaaaab6360b48 in btf_dump_emit_struct_def tools/lib/bpf/btf_dump.c:912
    #8 0xaaaab6360630 in btf_dump_emit_type tools/lib/bpf/btf_dump.c:798
    #9 0xaaaab635f720 in btf_dump__dump_type tools/lib/bpf/btf_dump.c:282
    #10 0xaaaab608523c in test_btf_dump_incremental tools/testing/selftests/bpf/prog_tests/btf_dump.c:236
    #11 0xaaaab6097530 in test_btf_dump tools/testing/selftests/bpf/prog_tests/btf_dump.c:875
    #12 0xaaaab6314ed0 in run_one_test tools/testing/selftests/bpf/test_progs.c:1062
    #13 0xaaaab631a0a8 in main tools/testing/selftests/bpf/test_progs.c:1697
    #14 0xffff9676d214 in __libc_start_main ../csu/libc-start.c:308
    #15 0xaaaab5d65990  (test_progs+0x185990)

0xffff927006db is located 11 bytes inside of 16-byte region [0xffff927006d0,0xffff927006e0)
freed by thread T0 here:
    #0 0xaaaab5e2c7c4 in realloc (test_progs+0x24c7c4)
    #1 0xaaaab634f4a0 in libbpf_reallocarray tools/lib/bpf/libbpf_internal.h:191
    #2 0xaaaab634f840 in libbpf_add_mem tools/lib/bpf/btf.c:163
    #3 0xaaaab636643c in strset_add_str_mem tools/lib/bpf/strset.c:106
    #4 0xaaaab6366560 in strset__add_str tools/lib/bpf/strset.c:157
    #5 0xaaaab6352d70 in btf__add_str tools/lib/bpf/btf.c:1519
    #6 0xaaaab6353e10 in btf__add_field tools/lib/bpf/btf.c:2032
    #7 0xaaaab6084fcc in test_btf_dump_incremental tools/testing/selftests/bpf/prog_tests/btf_dump.c:232
    #8 0xaaaab6097530 in test_btf_dump tools/testing/selftests/bpf/prog_tests/btf_dump.c:875
    #9 0xaaaab6314ed0 in run_one_test tools/testing/selftests/bpf/test_progs.c:1062
    #10 0xaaaab631a0a8 in main tools/testing/selftests/bpf/test_progs.c:1697
    #11 0xffff9676d214 in __libc_start_main ../csu/libc-start.c:308
    #12 0xaaaab5d65990  (test_progs+0x185990)

previously allocated by thread T0 here:
    #0 0xaaaab5e2c7c4 in realloc (test_progs+0x24c7c4)
    #1 0xaaaab634f4a0 in libbpf_reallocarray tools/lib/bpf/libbpf_internal.h:191
    #2 0xaaaab634f840 in libbpf_add_mem tools/lib/bpf/btf.c:163
    #3 0xaaaab636643c in strset_add_str_mem tools/lib/bpf/strset.c:106
    #4 0xaaaab6366560 in strset__add_str tools/lib/bpf/strset.c:157
    #5 0xaaaab6352d70 in btf__add_str tools/lib/bpf/btf.c:1519
    #6 0xaaaab6353ff0 in btf_add_enum_common tools/lib/bpf/btf.c:2070
    #7 0xaaaab6354080 in btf__add_enum tools/lib/bpf/btf.c:2102
    #8 0xaaaab6082f50 in test_btf_dump_incremental tools/testing/selftests/bpf/prog_tests/btf_dump.c:162
    #9 0xaaaab6097530 in test_btf_dump tools/testing/selftests/bpf/prog_tests/btf_dump.c:875
    #10 0xaaaab6314ed0 in run_one_test tools/testing/selftests/bpf/test_progs.c:1062
    #11 0xaaaab631a0a8 in main tools/testing/selftests/bpf/test_progs.c:1697
    #12 0xffff9676d214 in __libc_start_main ../csu/libc-start.c:308
    #13 0xaaaab5d65990  (test_progs+0x185990)

The reason is that the key stored in hash table name_map is a string
address, and the string memory is allocated by realloc() function, when
the memory is resized by realloc() later, the old memory may be freed,
so the address stored in name_map references to a freed memory, causing
use-after-free.

Fix it by storing duplicated string address in name_map.

Fixes: 919d2b1dbb07 ("libbpf: Allow modification of BTF and add btf__add_str API")
Signed-off-by: Xu Kuohai 
Signed-off-by: Andrii Nakryiko 
Acked-by: Martin KaFai Lau 
Link: https://lore.kernel.org/bpf/20221011120108.782373-2-xukuohai@huaweicloud.com

bpftool: Print newline before '}' for struct with padding only fields

2022-10-05T22:27:08+00:00

btf_dump_emit_struct_def attempts to print empty structures at a
single line, e.g. `struct empty {}`. However, it has to account for a
case when there are no regular but some padding fields in the struct.
In such case `vlen` would be zero, but size would be non-zero.

E.g. here is struct bpf_timer from vmlinux.h before this patch:

 struct bpf_timer {
 	long: 64;
	long: 64;};

And after this patch:

 struct bpf_dynptr {
 	long: 64;
	long: 64;
 };

Signed-off-by: Eduard Zingerman 
Signed-off-by: Andrii Nakryiko 
Link: https://lore.kernel.org/bpf/20221001104425.415768-1-eddyz87@gmail.com