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arm64: module: don't BUG when exceeding preallocated PLT count
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When PLTs are emitted at relocation time, we really should not exceed
the number that we counted when parsing the relocation tables, and so
currently, we BUG() on this condition. However, even though this is a
clear bug in this particular piece of code, we can easily recover by
failing to load the module.

So instead, return 0 from module_emit_plt_entry() if this condition
occurs, which is not a valid kernel address, and can hence serve as
a flag value that makes the relocation routine bail out.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
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Ard Biesheuvel authored and Will Deacon committed Mar 8, 2018
1 parent e03e61c commit 5e8307b
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Showing 2 changed files with 4 additions and 1 deletion.
3 changes: 2 additions & 1 deletion arch/arm64/kernel/module-plts.c
Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,8 @@ u64 module_emit_plt_entry(struct module *mod, void *loc, const Elf64_Rela *rela,
return (u64)&plt[i - 1];

pltsec->plt_num_entries++;
BUG_ON(pltsec->plt_num_entries > pltsec->plt_max_entries);
if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries))
return 0;

return (u64)&plt[i];
}
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2 changes: 2 additions & 0 deletions arch/arm64/kernel/module.c
Original file line number Diff line number Diff line change
Expand Up @@ -386,6 +386,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
ovf == -ERANGE) {
val = module_emit_plt_entry(me, loc, &rel[i], sym);
if (!val)
return -ENOEXEC;
ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2,
26, AARCH64_INSN_IMM_26);
}
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