forked from Openwrt/openwrt
ce51f27fb0
Backport an upstream Linux fix to prevent BPF kfunc functions from being
removed during linker optimization when building BTF-enabled vmlinux.
The telltale sign of this occurring is build log warnings (e.g. mips64el):
BTFIDS vmlinux
WARN: resolve_btfids: unresolved symbol bpf_verify_pkcs7_signature
WARN: resolve_btfids: unresolved symbol bpf_lookup_user_key
WARN: resolve_btfids: unresolved symbol bpf_lookup_system_key
WARN: resolve_btfids: unresolved symbol bpf_key_put
WARN: resolve_btfids: unresolved symbol bpf_iter_task_next
WARN: resolve_btfids: unresolved symbol bpf_iter_css_task_new
WARN: resolve_btfids: unresolved symbol bpf_get_file_xattr
WARN: resolve_btfids: unresolved symbol bpf_ct_insert_entry
NM System.map
SORTTAB vmlinux
Link: https://lore.kernel.org/bpf/ZlkoM6%2FPSxVcGM6X@kodidev-ubuntu/
Signed-off-by: Tony Ambardar <itugrok@yahoo.com>
Link: https://github.com/openwrt/openwrt/pull/15697
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
66 lines
2.7 KiB
Diff
66 lines
2.7 KiB
Diff
From ac507ed9882fd91a94657d68fe9ceac04b957103 Mon Sep 17 00:00:00 2001
|
|
From: Tony Ambardar <Tony.Ambardar@gmail.com>
|
|
Date: Sat, 1 Jun 2024 00:00:21 -0700
|
|
Subject: [PATCH 2/2] bpf: Harden __bpf_kfunc tag against linker kfunc removal
|
|
|
|
BPF kfuncs are often not directly referenced and may be inadvertently
|
|
removed by optimization steps during kernel builds, thus the __bpf_kfunc
|
|
tag mitigates against this removal by including the __used macro. However,
|
|
this macro alone does not prevent removal during linking, and may still
|
|
yield build warnings (e.g. on mips64el):
|
|
|
|
LD vmlinux
|
|
BTFIDS vmlinux
|
|
WARN: resolve_btfids: unresolved symbol bpf_verify_pkcs7_signature
|
|
WARN: resolve_btfids: unresolved symbol bpf_lookup_user_key
|
|
WARN: resolve_btfids: unresolved symbol bpf_lookup_system_key
|
|
WARN: resolve_btfids: unresolved symbol bpf_key_put
|
|
WARN: resolve_btfids: unresolved symbol bpf_iter_task_next
|
|
WARN: resolve_btfids: unresolved symbol bpf_iter_css_task_new
|
|
WARN: resolve_btfids: unresolved symbol bpf_get_file_xattr
|
|
WARN: resolve_btfids: unresolved symbol bpf_ct_insert_entry
|
|
WARN: resolve_btfids: unresolved symbol bpf_cgroup_release
|
|
WARN: resolve_btfids: unresolved symbol bpf_cgroup_from_id
|
|
WARN: resolve_btfids: unresolved symbol bpf_cgroup_acquire
|
|
WARN: resolve_btfids: unresolved symbol bpf_arena_free_pages
|
|
NM System.map
|
|
SORTTAB vmlinux
|
|
OBJCOPY vmlinux.32
|
|
|
|
Update the __bpf_kfunc tag to better guard against linker optimization by
|
|
including the new __retain compiler macro, which fixes the warnings above.
|
|
|
|
Verify the __retain macro with readelf by checking object flags for 'R':
|
|
|
|
$ readelf -Wa kernel/trace/bpf_trace.o
|
|
Section Headers:
|
|
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
|
|
...
|
|
[178] .text.bpf_key_put PROGBITS 00000000 6420 0050 00 AXR 0 0 8
|
|
...
|
|
Key to Flags:
|
|
...
|
|
R (retain), D (mbind), p (processor specific)
|
|
|
|
Link: https://lore.kernel.org/bpf/ZlmGoT9KiYLZd91S@krava/T/
|
|
Reported-by: kernel test robot <lkp@intel.com>
|
|
Closes: https://lore.kernel.org/r/202401211357.OCX9yllM-lkp@intel.com/
|
|
Fixes: 57e7c169cd6a ("bpf: Add __bpf_kfunc tag for marking kernel functions as kfuncs")
|
|
Cc: stable@vger.kernel.org # v6.6+
|
|
Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
|
|
---
|
|
include/linux/btf.h | 2 +-
|
|
1 file changed, 1 insertion(+), 1 deletion(-)
|
|
|
|
--- a/include/linux/btf.h
|
|
+++ b/include/linux/btf.h
|
|
@@ -81,7 +81,7 @@
|
|
* as to avoid issues such as the compiler inlining or eliding either a static
|
|
* kfunc, or a global kfunc in an LTO build.
|
|
*/
|
|
-#define __bpf_kfunc __used noinline
|
|
+#define __bpf_kfunc __used __retain noinline
|
|
|
|
/*
|
|
* Return the name of the passed struct, if exists, or halt the build if for
|