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6656cf1e97
Building a kernel via klp-build fails to link:
`__exitcall_aes_mod_exit' referenced in section `.klp.symid' of vmlinux.o: defined in discarded section `.exitcall.exit' of vmlinux.o
`__exitcall_dax_exit' referenced in section `.klp.symid' of vmlinux.o: defined in discarded section `.exitcall.exit' of vmlinux.o
`__exitcall_hid_exit' referenced in section `.klp.symid' of vmlinux.o: defined in discarded section `.exitcall.exit' of vmlinux.o
`__exitcall_usb_serial_module_exit' referenced in section `.klp.symid' of vmlinux.o: defined in discarded section `.exitcall.exit' of vmlinux.o
module_exit() on a built-in emits a static __exitcall_$fn pointer into
.exitcall.exit, which vmlinux.lds.h discards unconditionally via
EXIT_CALL. When two built-in translation units define a module_exit()
function of the same name, the resulting local symbols collide,
symid_needed() sees a duplicate and emits a .klp.symid entry for each,
referencing symbols the linker then throws away.
Same-named module_exit() functions are not rare:
dax_exit drivers/dax/device.c, drivers/dax/fsdev.c
hid_exit drivers/hid/hid-core.c, drivers/hid/usbhid/hid-core.c
aes_mod_exit arch/arm64/crypto/aes-ce-ccm-glue.c, lib/crypto/aes.c
usb_serial_module_exit module_usb_serial_driver() expands to this fixed
name in each of its ~49 users
The last one makes the collision structural rather than accidental: any
kernel with two built-in USB serial drivers has it. This is not arch
specific either; it only requires the objects to be built in rather than
modular, which is why a monolithic config trips it while a typical
distro config does not.
Add .exitcall.exit to the discarded section list so its symbols don't get
symids.
This is the same failure mode as "objtool/klp: Fix vmlinux .klp.symid
link error for .no_trim_symbol symbols", for another unconditionally
discarded allocated section.
Fixes: 029223d301 ("objtool/klp: Add .klp.symid for sympos disambiguation")
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Link: https://patch.msgid.link/m24igzlbxf.fsf@kernel.org
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
120 lines
2.9 KiB
C
120 lines
2.9 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Emit the .klp.symid table which allows "objtool klp diff" to reliably
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* disambiguate duplicate-named local symbols in vmlinux.
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*
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* Livepatch identifies a duplicate-named symbol by its position (sympos)
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* among the same-named kallsyms entries, counted in ascending address order
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* in the final linked vmlinux. That order can't be derived from vmlinux.o
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* alone: the final link reorders sub-sections (.text.unlikely*, .data..*,
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* etc).
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*
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* Bridge the gap with a table which survives the final link: a single
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* non-alloc section containing an array of { id, addr } entries, where
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* 'id' is a unique counter identifier and 'addr' has a relocation to the
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* symbol. The linker copies 'id' verbatim and resolves 'addr' to the symbol's
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* final address.
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*
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* The table is only emitted for vmlinux.o, and only when klp-build asks for it
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* with KLP_SYMIDS=1, which adds --klp-symids to the vmlinux.o objtool run.
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*
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* It can't survive --gc-sections, which sweeps the whole section; klp-build
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* rejects CONFIG_LD_DEAD_CODE_DATA_ELIMINATION.
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*/
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#include <linux/string.h>
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#include <objtool/objtool.h>
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#include <objtool/warn.h>
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#include <objtool/endianness.h>
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#include <objtool/klp.h>
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static const char * const discarded_secs[] = {
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".discard",
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".exitcall.exit",
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".modinfo",
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".no_trim_symbol",
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"__tracepoint_check",
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};
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static bool discarded_sec(struct section *sec)
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{
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if (!(sec->sh.sh_flags & SHF_ALLOC))
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return true;
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for (int i = 0; i < ARRAY_SIZE(discarded_secs); i++)
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if (strstarts(sec->name, discarded_secs[i]))
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return true;
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return false;
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}
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static bool symid_needed(struct elf *elf, struct symbol *sym)
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{
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struct symbol *s;
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if (!is_local_sym(sym) || is_undef_sym(sym))
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return false;
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if (!is_func_sym(sym) && !is_object_sym(sym))
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return false;
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if (is_prefix_func(sym))
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return false;
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if (discarded_sec(sym->sec))
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return false;
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for_each_sym_by_name(elf, sym->name, s) {
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if (s == sym || is_sec_sym(s) || is_file_sym(s) || is_undef_sym(s))
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continue;
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return true;
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}
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return false;
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}
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int klp_create_symid_sections(struct objtool_file *file)
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{
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struct elf *elf = file->elf;
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struct klp_symid *symids;
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struct section *sec;
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struct symbol *sym;
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u64 nr = 0, i = 0;
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if (!str_ends_with(objname, "vmlinux.o"))
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return 0;
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for_each_sym(elf, sym)
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if (symid_needed(elf, sym))
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nr++;
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if (!nr)
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return 0;
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sec = elf_create_section(elf, KLP_SYMID_SEC, 0, sizeof(struct klp_symid),
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SHT_PROGBITS, 8, 0);
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if (!sec)
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return -1;
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symids = elf_add_data(elf, sec, NULL, nr * sizeof(struct klp_symid));
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if (!symids)
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return -1;
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for_each_sym(elf, sym) {
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if (!symid_needed(elf, sym))
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continue;
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symids[i].id = bswap_if_needed(elf, i);
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if (!elf_create_reloc(elf, sec,
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i * sizeof(struct klp_symid) +
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offsetof(struct klp_symid, addr),
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sym, 0, R_ABS64))
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return -1;
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i++;
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}
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return 0;
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}
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