Unverified Commit 0cff8bff authored Feb 21, 2020 by Vincent Chen Committed by Palmer Dabbelt Mar 03, 2020

riscv: avoid the PIC offset of static percpu data in module beyond 2G limits



The compiler uses the PIC-relative method to access static variables
instead of GOT when the code model is PIC. Therefore, the limitation of
the access range from the instruction to the symbol address is +-2GB.
Under this circumstance, the kernel cannot load a kernel module if this
module has static per-CPU symbols declared by DEFINE_PER_CPU(). The reason
is that kernel relocates the .data..percpu section of the kernel module to
the end of kernel's .data..percpu. Hence, the distance between the per-CPU
symbols and the instruction will exceed the 2GB limits. To solve this
problem, the kernel should place the loaded module in the memory area
[&_end-2G, VMALLOC_END].

Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Suggested-by: Alexandre Ghiti <alex@ghiti.fr>
Suggested-by: Anup Patel <anup@brainfault.org>
Tested-by: Alexandre Ghiti <alex@ghiti.fr>
Tested-by: Carlos de Paula <me@carlosedp.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

parent 98d54f81

arch/riscv/kernel/module.c

+16 −0

Original line number	Diff line number	Diff line
		@@ -8,6 +8,10 @@
		#include <linux/err.h>
		#include <linux/errno.h>
		#include <linux/moduleloader.h>
		#include <linux/vmalloc.h>
		#include <linux/sizes.h>
		#include <asm/pgtable.h>
		#include <asm/sections.h>

		static int apply_r_riscv_32_rela(struct module me, u32 location, Elf_Addr v)
		{
		@@ -386,3 +390,15 @@ int apply_relocate_add(Elf_Shdr sechdrs, const char strtab,

		return 0;
		}

		#if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
		#define VMALLOC_MODULE_START \
		max(PFN_ALIGN((unsigned long)&_end - SZ_2G), VMALLOC_START)
		void *module_alloc(unsigned long size)
		{
		return __vmalloc_node_range(size, 1, VMALLOC_MODULE_START,
		VMALLOC_END, GFP_KERNEL,
		PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
		__builtin_return_address(0));
		}
		#endif

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