ARM: 8220/1: allow modules outside of bl range

Loading modules far away from the kernel in memory is problematic
because the 'bl' instruction only has limited reach, and modules are not
built with PLTs. Instead of using the -mlong-calls option (which affects
all compiler emitted bl instructions, but not the ones in assembler),
this patch allocates some additional space at module load time, and
populates it with PLT like veneers when encountering relocations that
are out of range.

This should work with all relocations against symbols exported by the
kernel, including those resulting from GCC generated implicit function
calls for ftrace etc.

The module memory size increases by about 5% on average, regardless of
whether any PLT entries were actually needed. However, due to the page
based rounding that occurs when allocating module memory, the average
memory footprint increase is negligible.

Reviewed-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 11 insertions, 1 deletions

diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
index ed690c49ef93..e358b7966c06 100644
--- a/arch/arm/include/asm/module.h
+++ b/arch/arm/include/asm/module.h
@@ -16,11 +16,21 @@ enum {
 	ARM_SEC_UNLIKELY,
 	ARM_SEC_MAX,
 };
+#endif
 
 struct mod_arch_specific {
+#ifdef CONFIG_ARM_UNWIND
 	struct unwind_table *unwind[ARM_SEC_MAX];
-};
 #endif
+#ifdef CONFIG_ARM_MODULE_PLTS
+	struct elf32_shdr   *core_plt;
+	struct elf32_shdr   *init_plt;
+	int		    core_plt_count;
+	int		    init_plt_count;
+#endif
+};
+
+u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val);
 
 /*
  * Add the ARM architecture version to the version magic string