arm64: module: split core and init PLT sections

The arm64 module PLT code allocates all PLT entries in a single core
section, since the overhead of having a separate init PLT section is
not justified by the small number of PLT entries usually required for
init code.

However, the core and init module regions are allocated independently,
and there is a corner case where the core region may be allocated from
the VMALLOC region if the dedicated module region is exhausted, but the
init region, being much smaller, can still be allocated from the module
region. This leads to relocation failures if the distance between those
regions exceeds 128 MB. (In fact, this corner case is highly unlikely to
occur on arm64, but the issue has been observed on ARM, whose module
region is much smaller).

So split the core and init PLT regions, and name the latter ".init.plt"
so it gets allocated along with (and sufficiently close to) the .init
sections that it serves. Also, given that init PLT entries may need to
be emitted for branches that target the core module, modify the logic
that disregards defined symbols to only disregard symbols that are
defined in the same section as the relocated branch instruction.

Since there may now be two PLT entries associated with each entry in
the symbol table, we can no longer hijack the symbol::st_size fields
to record the addresses of PLT entries as we emit them for zero-addend
relocations. So instead, perform an explicit comparison to check for
duplicate entries.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h
index e12af6754634..d57693f5d4ec 100644
--- a/arch/arm64/include/asm/module.h
+++ b/arch/arm64/include/asm/module.h
@@ -21,14 +21,19 @@
 #define MODULE_ARCH_VERMAGIC	"aarch64"
 
 #ifdef CONFIG_ARM64_MODULE_PLTS
-struct mod_arch_specific {
+struct mod_plt_sec {
 	struct elf64_shdr	*plt;
 	int			plt_num_entries;
 	int			plt_max_entries;
 };
+
+struct mod_arch_specific {
+	struct mod_plt_sec	core;
+	struct mod_plt_sec	init;
+};
 #endif
 
-u64 module_emit_plt_entry(struct module *mod, const Elf64_Rela *rela,
+u64 module_emit_plt_entry(struct module *mod, void *loc, const Elf64_Rela *rela,
 			  Elf64_Sym *sym);
 
 #ifdef CONFIG_RANDOMIZE_BASE