linux-stable.git/kernel/bpf, branch v5.4.71 Linux kernel stable tree bpf: Fix sysfs export of empty BTF section 2020-10-14T08:32:58+00:00 Tony Ambardar tony.ambardar@gmail.com 2020-09-20T05:01:33+00:00 67a57230b4bfb377cd479c9b32d1e2ab70bc96d1 commit e23bb04b0c938588eae41b7f4712b722290ed2b8 upstream. If BTF data is missing or removed from the ELF section it is still exported via sysfs as a zero-length file: root@OpenWrt:/# ls -l /sys/kernel/btf/vmlinux -r--r--r-- 1 root root 0 Jul 18 02:59 /sys/kernel/btf/vmlinux Moreover, reads from this file succeed and leak kernel data: root@OpenWrt:/# hexdump -C /sys/kernel/btf/vmlinux|head -10 000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 000cc0 00 00 00 00 00 00 00 00 00 00 00 00 80 83 b0 80 |................| 000cd0 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 000ce0 00 00 00 00 00 00 00 00 00 00 00 00 57 ac 6e 9d |............W.n.| 000cf0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 002650 00 00 00 00 00 00 00 10 00 00 00 01 00 00 00 01 |................| 002660 80 82 9a c4 80 85 97 80 81 a9 51 68 00 00 00 02 |..........Qh....| 002670 80 25 44 dc 80 85 97 80 81 a9 50 24 81 ab c4 60 |.%D.......P$...`| This situation was first observed with kernel 5.4.x, cross-compiled for a MIPS target system. Fix by adding a sanity-check for export of zero-length data sections. Fixes: 341dfcf8d78e ("btf: expose BTF info through sysfs") Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Andrii Nakryiko <andriin@fb.com> Link: https://lore.kernel.org/bpf/b38db205a66238f70823039a8c531535864eaac5.1600417359.git.Tony.Ambardar@gmail.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit e23bb04b0c938588eae41b7f4712b722290ed2b8 upstream.

If BTF data is missing or removed from the ELF section it is still exported
via sysfs as a zero-length file:

  root@OpenWrt:/# ls -l /sys/kernel/btf/vmlinux
  -r--r--r--    1 root    root    0 Jul 18 02:59 /sys/kernel/btf/vmlinux

Moreover, reads from this file succeed and leak kernel data:

  root@OpenWrt:/# hexdump -C /sys/kernel/btf/vmlinux|head -10
  000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
  *
  000cc0 00 00 00 00 00 00 00 00 00 00 00 00 80 83 b0 80 |................|
  000cd0 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
  000ce0 00 00 00 00 00 00 00 00 00 00 00 00 57 ac 6e 9d |............W.n.|
  000cf0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
  *
  002650 00 00 00 00 00 00 00 10 00 00 00 01 00 00 00 01 |................|
  002660 80 82 9a c4 80 85 97 80 81 a9 51 68 00 00 00 02 |..........Qh....|
  002670 80 25 44 dc 80 85 97 80 81 a9 50 24 81 ab c4 60 |.%D.......P$...`|

This situation was first observed with kernel 5.4.x, cross-compiled for a
MIPS target system. Fix by adding a sanity-check for export of zero-length
data sections.

Fixes: 341dfcf8d78e ("btf: expose BTF info through sysfs")
Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/b38db205a66238f70823039a8c531535864eaac5.1600417359.git.Tony.Ambardar@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
bpf: Fix a rcu warning for bpffs map pretty-print 2020-10-01T11:18:19+00:00 Yonghong Song yhs@fb.com 2020-09-16T00:44:01+00:00 43cdb648e1da7b195eba564c5af5a2c320f77dce [ Upstream commit ce880cb825fcc22d4e39046a6c3a3a7f6603883d ] Running selftest ./btf_btf -p the kernel had the following warning: [ 51.528185] WARNING: CPU: 3 PID: 1756 at kernel/bpf/hashtab.c:717 htab_map_get_next_key+0x2eb/0x300 [ 51.529217] Modules linked in: [ 51.529583] CPU: 3 PID: 1756 Comm: test_btf Not tainted 5.9.0-rc1+ #878 [ 51.530346] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-1.el7.centos 04/01/2014 [ 51.531410] RIP: 0010:htab_map_get_next_key+0x2eb/0x300 ... [ 51.542826] Call Trace: [ 51.543119] map_seq_next+0x53/0x80 [ 51.543528] seq_read+0x263/0x400 [ 51.543932] vfs_read+0xad/0x1c0 [ 51.544311] ksys_read+0x5f/0xe0 [ 51.544689] do_syscall_64+0x33/0x40 [ 51.545116] entry_SYSCALL_64_after_hwframe+0x44/0xa9 The related source code in kernel/bpf/hashtab.c: 709 static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key) 710 { 711 struct bpf_htab *htab = container_of(map, struct bpf_htab, map); 712 struct hlist_nulls_head *head; 713 struct htab_elem *l, *next_l; 714 u32 hash, key_size; 715 int i = 0; 716 717 WARN_ON_ONCE(!rcu_read_lock_held()); In kernel/bpf/inode.c, bpffs map pretty print calls map->ops->map_get_next_key() without holding a rcu_read_lock(), hence causing the above warning. To fix the issue, just surrounding map->ops->map_get_next_key() with rcu read lock. Fixes: a26ca7c982cb ("bpf: btf: Add pretty print support to the basic arraymap") Reported-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Andrii Nakryiko <andriin@fb.com> Cc: Martin KaFai Lau <kafai@fb.com> Link: https://lore.kernel.org/bpf/20200916004401.146277-1-yhs@fb.com Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit ce880cb825fcc22d4e39046a6c3a3a7f6603883d ]

Running selftest
  ./btf_btf -p
the kernel had the following warning:
  [   51.528185] WARNING: CPU: 3 PID: 1756 at kernel/bpf/hashtab.c:717 htab_map_get_next_key+0x2eb/0x300
  [   51.529217] Modules linked in:
  [   51.529583] CPU: 3 PID: 1756 Comm: test_btf Not tainted 5.9.0-rc1+ #878
  [   51.530346] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-1.el7.centos 04/01/2014
  [   51.531410] RIP: 0010:htab_map_get_next_key+0x2eb/0x300
  ...
  [   51.542826] Call Trace:
  [   51.543119]  map_seq_next+0x53/0x80
  [   51.543528]  seq_read+0x263/0x400
  [   51.543932]  vfs_read+0xad/0x1c0
  [   51.544311]  ksys_read+0x5f/0xe0
  [   51.544689]  do_syscall_64+0x33/0x40
  [   51.545116]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

The related source code in kernel/bpf/hashtab.c:
  709 static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
  710 {
  711         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
  712         struct hlist_nulls_head *head;
  713         struct htab_elem *l, *next_l;
  714         u32 hash, key_size;
  715         int i = 0;
  716
  717         WARN_ON_ONCE(!rcu_read_lock_held());

In kernel/bpf/inode.c, bpffs map pretty print calls map->ops->map_get_next_key()
without holding a rcu_read_lock(), hence causing the above warning.
To fix the issue, just surrounding map->ops->map_get_next_key() with rcu read lock.

Fixes: a26ca7c982cb ("bpf: btf: Add pretty print support to the basic arraymap")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Cc: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200916004401.146277-1-yhs@fb.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
bpf: Remove recursion prevention from rcu free callback 2020-10-01T11:17:36+00:00 Thomas Gleixner tglx@linutronix.de 2020-02-24T14:01:39+00:00 f60007c9e91402d936e300913eed62fa7fc2e54b [ Upstream commit 8a37963c7ac9ecb7f86f8ebda020e3f8d6d7b8a0 ] If an element is freed via RCU then recursion into BPF instrumentation functions is not a concern. The element is already detached from the map and the RCU callback does not hold any locks on which a kprobe, perf event or tracepoint attached BPF program could deadlock. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200224145643.259118710@linutronix.de Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 8a37963c7ac9ecb7f86f8ebda020e3f8d6d7b8a0 ]

If an element is freed via RCU then recursion into BPF instrumentation
functions is not a concern. The element is already detached from the map
and the RCU callback does not hold any locks on which a kprobe, perf event
or tracepoint attached BPF program could deadlock.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200224145643.259118710@linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
bpf: sockmap: Require attach_bpf_fd when detaching a program 2020-08-07T07:34:02+00:00 Lorenz Bauer lmb@cloudflare.com 2020-06-29T09:56:28+00:00 ca7ace8fd26d9ae4be3cf69f474ddcfb0e8506ce commit bb0de3131f4c60a9bf976681e0fe4d1e55c7a821 upstream. The sockmap code currently ignores the value of attach_bpf_fd when detaching a program. This is contrary to the usual behaviour of checking that attach_bpf_fd represents the currently attached program. Ensure that attach_bpf_fd is indeed the currently attached program. It turns out that all sockmap selftests already do this, which indicates that this is unlikely to cause breakage. Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface") Signed-off-by: Lorenz Bauer <lmb@cloudflare.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200629095630.7933-5-lmb@cloudflare.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit bb0de3131f4c60a9bf976681e0fe4d1e55c7a821 upstream.

The sockmap code currently ignores the value of attach_bpf_fd when
detaching a program. This is contrary to the usual behaviour of
checking that attach_bpf_fd represents the currently attached
program.

Ensure that attach_bpf_fd is indeed the currently attached
program. It turns out that all sockmap selftests already do this,
which indicates that this is unlikely to cause breakage.

Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200629095630.7933-5-lmb@cloudflare.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
bpf: Fix map leak in HASH_OF_MAPS map 2020-08-05T07:59:48+00:00 Andrii Nakryiko andriin@fb.com 2020-07-29T04:09:12+00:00 fe58e3dd6e119c6d41fd535429b0f1e83b5433d2 [ Upstream commit 1d4e1eab456e1ee92a94987499b211db05f900ea ] Fix HASH_OF_MAPS bug of not putting inner map pointer on bpf_map_elem_update() operation. This is due to per-cpu extra_elems optimization, which bypassed free_htab_elem() logic doing proper clean ups. Make sure that inner map is put properly in optimized case as well. Fixes: 8c290e60fa2a ("bpf: fix hashmap extra_elems logic") Signed-off-by: Andrii Nakryiko <andriin@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20200729040913.2815687-1-andriin@fb.com Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 1d4e1eab456e1ee92a94987499b211db05f900ea ]

Fix HASH_OF_MAPS bug of not putting inner map pointer on bpf_map_elem_update()
operation. This is due to per-cpu extra_elems optimization, which bypassed
free_htab_elem() logic doing proper clean ups. Make sure that inner map is put
properly in optimized case as well.

Fixes: 8c290e60fa2a ("bpf: fix hashmap extra_elems logic")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20200729040913.2815687-1-andriin@fb.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
bpf: Check correct cred for CAP_SYSLOG in bpf_dump_raw_ok() 2020-07-16T06:16:45+00:00 Kees Cook keescook@chromium.org 2020-07-02T22:45:23+00:00 baef8d1027b0c037128c8be56338e6e066317e68 commit 63960260457a02af2a6cb35d75e6bdb17299c882 upstream. When evaluating access control over kallsyms visibility, credentials at open() time need to be used, not the "current" creds (though in BPF's case, this has likely always been the same). Plumb access to associated file->f_cred down through bpf_dump_raw_ok() and its callers now that kallsysm_show_value() has been refactored to take struct cred. Cc: Alexei Starovoitov <ast@kernel.org> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: bpf@vger.kernel.org Cc: stable@vger.kernel.org Fixes: 7105e828c087 ("bpf: allow for correlation of maps and helpers in dump") Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 63960260457a02af2a6cb35d75e6bdb17299c882 upstream.

When evaluating access control over kallsyms visibility, credentials at
open() time need to be used, not the "current" creds (though in BPF's
case, this has likely always been the same). Plumb access to associated
file->f_cred down through bpf_dump_raw_ok() and its callers now that
kallsysm_show_value() has been refactored to take struct cred.

Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: bpf@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: 7105e828c087 ("bpf: allow for correlation of maps and helpers in dump")
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
bpf: Don't return EINVAL from {get,set}sockopt when optlen > PAGE_SIZE 2020-06-30T19:36:56+00:00 Stanislav Fomichev sdf@google.com 2020-06-17T01:04:14+00:00 f1ee7d3a2c1ab17802321879c9a62ca690e71ab9 [ Upstream commit d8fe449a9c51a37d844ab607e14e2f5c657d3cf2 ] Attaching to these hooks can break iptables because its optval is usually quite big, or at least bigger than the current PAGE_SIZE limit. David also mentioned some SCTP options can be big (around 256k). For such optvals we expose only the first PAGE_SIZE bytes to the BPF program. BPF program has two options: 1. Set ctx->optlen to 0 to indicate that the BPF's optval should be ignored and the kernel should use original userspace value. 2. Set ctx->optlen to something that's smaller than the PAGE_SIZE. v5: * use ctx->optlen == 0 with trimmed buffer (Alexei Starovoitov) * update the docs accordingly v4: * use temporary buffer to avoid optval == optval_end == NULL; this removes the corner case in the verifier that might assume non-zero PTR_TO_PACKET/PTR_TO_PACKET_END. v3: * don't increase the limit, bypass the argument v2: * proper comments formatting (Jakub Kicinski) Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks") Signed-off-by: Stanislav Fomichev <sdf@google.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Cc: David Laight <David.Laight@ACULAB.COM> Link: https://lore.kernel.org/bpf/20200617010416.93086-1-sdf@google.com Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit d8fe449a9c51a37d844ab607e14e2f5c657d3cf2 ]

Attaching to these hooks can break iptables because its optval is
usually quite big, or at least bigger than the current PAGE_SIZE limit.
David also mentioned some SCTP options can be big (around 256k).

For such optvals we expose only the first PAGE_SIZE bytes to
the BPF program. BPF program has two options:
1. Set ctx->optlen to 0 to indicate that the BPF's optval
   should be ignored and the kernel should use original userspace
   value.
2. Set ctx->optlen to something that's smaller than the PAGE_SIZE.

v5:
* use ctx->optlen == 0 with trimmed buffer (Alexei Starovoitov)
* update the docs accordingly

v4:
* use temporary buffer to avoid optval == optval_end == NULL;
  this removes the corner case in the verifier that might assume
  non-zero PTR_TO_PACKET/PTR_TO_PACKET_END.

v3:
* don't increase the limit, bypass the argument

v2:
* proper comments formatting (Jakub Kicinski)

Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks")
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Cc: David Laight <David.Laight@ACULAB.COM>
Link: https://lore.kernel.org/bpf/20200617010416.93086-1-sdf@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
devmap: Use bpf_map_area_alloc() for allocating hash buckets 2020-06-30T19:36:56+00:00 Toke Høiland-Jørgensen toke@redhat.com 2020-06-16T14:28:29+00:00 0f3aa6c6d6adf4578164e9c5b164dd6e4d6b4800 [ Upstream commit 99c51064fb06146b3d494b745c947e438a10aaa7 ] Syzkaller discovered that creating a hash of type devmap_hash with a large number of entries can hit the memory allocator limit for allocating contiguous memory regions. There's really no reason to use kmalloc_array() directly in the devmap code, so just switch it to the existing bpf_map_area_alloc() function that is used elsewhere. Fixes: 6f9d451ab1a3 ("xdp: Add devmap_hash map type for looking up devices by hashed index") Reported-by: Xiumei Mu <xmu@redhat.com> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: John Fastabend <john.fastabend@gmail.com> Link: https://lore.kernel.org/bpf/20200616142829.114173-1-toke@redhat.com Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 99c51064fb06146b3d494b745c947e438a10aaa7 ]

Syzkaller discovered that creating a hash of type devmap_hash with a large
number of entries can hit the memory allocator limit for allocating
contiguous memory regions. There's really no reason to use kmalloc_array()
directly in the devmap code, so just switch it to the existing
bpf_map_area_alloc() function that is used elsewhere.

Fixes: 6f9d451ab1a3 ("xdp: Add devmap_hash map type for looking up devices by hashed index")
Reported-by: Xiumei Mu <xmu@redhat.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200616142829.114173-1-toke@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
bpf: Fix map permissions check 2020-06-22T07:31:11+00:00 Anton Protopopov a.s.protopopov@gmail.com 2020-05-27T18:56:59+00:00 215a256bc8dd7ef6bc52f3fd697027a7275d1c27 [ Upstream commit 1ea0f9120c8ce105ca181b070561df5cbd6bc049 ] The map_lookup_and_delete_elem() function should check for both FMODE_CAN_WRITE and FMODE_CAN_READ permissions because it returns a map element to user space. Fixes: bd513cd08f10 ("bpf: add MAP_LOOKUP_AND_DELETE_ELEM syscall") Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20200527185700.14658-5-a.s.protopopov@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 1ea0f9120c8ce105ca181b070561df5cbd6bc049 ]

The map_lookup_and_delete_elem() function should check for both FMODE_CAN_WRITE
and FMODE_CAN_READ permissions because it returns a map element to user space.

Fixes: bd513cd08f10 ("bpf: add MAP_LOOKUP_AND_DELETE_ELEM syscall")
Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200527185700.14658-5-a.s.protopopov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
bpf: Support llvm-objcopy for vmlinux BTF 2020-06-17T14:40:20+00:00 Fangrui Song maskray@google.com 2020-03-18T22:27:46+00:00 f04d1e880f17b935b5a181d446ff82b4193eee85 commit 90ceddcb495008ac8ba7a3dce297841efcd7d584 upstream. Simplify gen_btf logic to make it work with llvm-objcopy. The existing 'file format' and 'architecture' parsing logic is brittle and does not work with llvm-objcopy/llvm-objdump. 'file format' output of llvm-objdump>=11 will match GNU objdump, but 'architecture' (bfdarch) may not. .BTF in .tmp_vmlinux.btf is non-SHF_ALLOC. Add the SHF_ALLOC flag because it is part of vmlinux image used for introspection. C code can reference the section via linker script defined __start_BTF and __stop_BTF. This fixes a small problem that previous .BTF had the SHF_WRITE flag (objcopy -I binary -O elf* synthesized .data). Additionally, `objcopy -I binary` synthesized symbols _binary__btf_vmlinux_bin_start and _binary__btf_vmlinux_bin_stop (not used elsewhere) are replaced with more commonplace __start_BTF and __stop_BTF. Add 2>/dev/null because GNU objcopy (but not llvm-objcopy) warns "empty loadable segment detected at vaddr=0xffffffff81000000, is this intentional?" We use a dd command to change the e_type field in the ELF header from ET_EXEC to ET_REL so that lld will accept .btf.vmlinux.bin.o. Accepting ET_EXEC as an input file is an extremely rare GNU ld feature that lld does not intend to support, because this is error-prone. The output section description .BTF in include/asm-generic/vmlinux.lds.h avoids potential subtle orphan section placement issues and suppresses --orphan-handling=warn warnings. Fixes: df786c9b9476 ("bpf: Force .BTF section start to zero when dumping from vmlinux") Fixes: cb0cc635c7a9 ("powerpc: Include .BTF section") Reported-by: Nathan Chancellor <natechancellor@gmail.com> Signed-off-by: Fangrui Song <maskray@google.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Tested-by: Stanislav Fomichev <sdf@google.com> Tested-by: Andrii Nakryiko <andriin@fb.com> Reviewed-by: Stanislav Fomichev <sdf@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Acked-by: Andrii Nakryiko <andriin@fb.com> Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc) Link: https://github.com/ClangBuiltLinux/linux/issues/871 Link: https://lore.kernel.org/bpf/20200318222746.173648-1-maskray@google.com Signed-off-by: Maria Teguiani <teguiani@google.com> Tested-by: Matthias Maennich <maennich@google.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 90ceddcb495008ac8ba7a3dce297841efcd7d584 upstream.

Simplify gen_btf logic to make it work with llvm-objcopy. The existing
'file format' and 'architecture' parsing logic is brittle and does not
work with llvm-objcopy/llvm-objdump.

'file format' output of llvm-objdump>=11 will match GNU objdump, but
'architecture' (bfdarch) may not.

.BTF in .tmp_vmlinux.btf is non-SHF_ALLOC. Add the SHF_ALLOC flag
because it is part of vmlinux image used for introspection. C code
can reference the section via linker script defined __start_BTF and
__stop_BTF. This fixes a small problem that previous .BTF had the
SHF_WRITE flag (objcopy -I binary -O elf* synthesized .data).

Additionally, `objcopy -I binary` synthesized symbols
_binary__btf_vmlinux_bin_start and _binary__btf_vmlinux_bin_stop (not
used elsewhere) are replaced with more commonplace __start_BTF and
__stop_BTF.

Add 2>/dev/null because GNU objcopy (but not llvm-objcopy) warns
"empty loadable segment detected at vaddr=0xffffffff81000000, is this intentional?"

We use a dd command to change the e_type field in the ELF header from
ET_EXEC to ET_REL so that lld will accept .btf.vmlinux.bin.o.  Accepting
ET_EXEC as an input file is an extremely rare GNU ld feature that lld
does not intend to support, because this is error-prone.

The output section description .BTF in include/asm-generic/vmlinux.lds.h
avoids potential subtle orphan section placement issues and suppresses
--orphan-handling=warn warnings.

Fixes: df786c9b9476 ("bpf: Force .BTF section start to zero when dumping from vmlinux")
Fixes: cb0cc635c7a9 ("powerpc: Include .BTF section")
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Fangrui Song <maskray@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Stanislav Fomichev <sdf@google.com>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Link: https://github.com/ClangBuiltLinux/linux/issues/871
Link: https://lore.kernel.org/bpf/20200318222746.173648-1-maskray@google.com
Signed-off-by: Maria Teguiani <teguiani@google.com>
Tested-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>