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