sysfs: cannot create duplicate filename '/kernel/kpatch/patches/kpatch_fix_stack_randomization/functions/load_elf_binary'

[arighi]

I get this error if I try to apply this patch live to a 3.12.38 (vanilla):
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=4e7c22d447bb6d7e37bfe39ff658486ae78e8d77

When I compile the fix kpatch-build says:
...
Extracting new and modified ELF sections
mmap.o: changed function: stack_maxrandom_size
mmap.o: changed function: arch_pick_mmap_layout
compat_binfmt_elf.o: changed function: load_elf_binary
binfmt_elf.o: changed function: load_elf_binary

So, IIUC the reason of the duplicate load_elf_binary it's because kpatch-build thinks there's a load_elf_binary() also in compat_binfmt_elf.c... but apparently it's defined only in fs/binfmt_elf.c...

Could you clarify or point out how to address this problem? Any help appreciated.

Thanks!

Full kernel oops:
[ 1137.462576] ------------[ cut here ]------------
[ 1137.462685] WARNING: CPU: 1 PID: 31107 at fs/sysfs/dir.c:526 sysfs_add_one+0xa5/0xd0()
[ 1137.462695] sysfs: cannot create duplicate filename '/kernel/kpatch/patches/kpatch_fix_stack_randomization/functions/load_elf_binary'
[ 1137.462701] Modules linked in: kpatch_fix_stack_randomization(O+) kpatch(O) ipt_MASQUERADE iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack ip_tables x_tables arc4 ath9k ath9k_common ath9k_hw dell_wmi sparse_keymap x86_pkg_temp_thermal kvm_intel kvm ath dell_laptop mac80211 dcdbas ath3k btusb snd_hda_codec_hdmi snd_hda_codec_realtek bluetooth snd_hda_intel snd_hda_codec snd_hwdep snd_pcm snd_page_alloc snd_seq_midi snd_seq_midi_event uvcvideo cfg80211 snd_rawmidi nfsd videobuf2_vmalloc videobuf2_memops videobuf2_core snd_seq videodev snd_timer snd_seq_device auth_rpcgss oid_registry joydev snd nfs parport_pc serio_raw ppdev soundcore lp wmi lockd parport mac_hid sunrpc raid1 psmouse i915 i2c_algo_bit drm_kms_helper drm video
[ 1137.462893] CPU: 1 PID: 31107 Comm: insmod Tainted: G O 3.12.38 #1
[ 1137.462895] Hardware name: Dell Inc. Dell System XPS L322X/0PJHXN, BIOS A09 05/15/2013
[ 1137.462897] 0000000000000009 ffff88009a571b00 ffffffff816b7c74 ffff88009a571b48
[ 1137.462903] ffff88009a571b38 ffffffff8104e23d 00000000ffffffef ffff88009a3fabe0
[ 1137.462908] ffff88009a571be0 ffff8802319e6000 0000000000000000 ffff88009a571b98
[ 1137.462914] Call Trace:
[ 1137.462920] [] dump_stack+0x54/0x74
[ 1137.462925] [] warn_slowpath_common+0x7d/0xa0
[ 1137.462929] [] warn_slowpath_fmt+0x4c/0x50
[ 1137.462932] [] sysfs_add_one+0xa5/0xd0
[ 1137.462936] [] create_dir+0x74/0xd0
[ 1137.462940] [] sysfs_create_dir+0x89/0xe0
[ 1137.462945] [] ? kvasprintf+0x6b/0x80
[ 1137.462950] [] kobject_add_internal+0xbb/0x2b0
[ 1137.462953] [] kobject_add+0x65/0xb0
[ 1137.462958] [] ? __kmalloc+0x1b0/0x1e0
[ 1137.462963] [] ? kzalloc.constprop.6+0xe/0x10 [kpatch_fix_stack_randomization]
[ 1137.462968] [] patch_init+0x1c1/0x1000 [kpatch_fix_stack_randomization]
[ 1137.462973] [] ? 0xffffffffa0680fff
[ 1137.462978] [] do_one_initcall+0x112/0x170
[ 1137.462983] [] ? set_memory_nx+0x43/0x50
[ 1137.462989] [] load_module+0x1caa/0x24f0
[ 1137.462992] [] ? symbol_put_addr+0x40/0x40
[ 1137.463017] [] SyS_finit_module+0x7e/0x80
[ 1137.463032] [] system_call_fastpath+0x16/0x1b
[ 1137.463040] ---[ end trace daaae26ff27a47fc ]---

[jpoimboe]

So, IIUC the reason of the duplicate load_elf_binary it's because kpatch-build thinks there's a load_elf_binary() also in compat_binfmt_elf.c... but apparently it's defined only in fs/binfmt_elf.c...

Actually compat_binfmt_elf.c has #include "binfmt_elf.c", so it looks to me like kpatch-build is correctly detecting a change to both files.

The fact that kpatch doesn't allow the patching of two functions with the same name is probably a bug. But that will be going away soon when we change the kpatch sysfs interface to be more like upstream livepatch.

I think you should be able to work around this issue by adding the following change to your patch.

At the end of fs/compat_binfmt_elf.c:

#include "kpatch-macros.h"
KPATCH_IGNORE_FUNCTION(load_elf_binary);

That should tell kpatch-build to ignore the change to load_elf_binary() in compat_binfmt.c.

[arighi]

The suggested workaround works very well. For my point of view we can close this issue.

Thanks!