[PATCH AUTOSEL 4.19 14/20] riscv: avoid the PIC offset of static percpu data in module beyond 2G limits

[Sasha Levin]

From: Vincent Chen <vincent.chen@xxxxxxxxxx>

[ Upstream commit 0cff8bff7af886af0923d5c91776cd51603e531f ]

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@xxxxxxxxxx>
Suggested-by: Alexandre Ghiti <alex@xxxxxxxx>
Suggested-by: Anup Patel <anup@xxxxxxxxxxxxxx>
Tested-by: Alexandre Ghiti <alex@xxxxxxxx>
Tested-by: Carlos de Paula <me@xxxxxxxxxxxxx>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/riscv/kernel/module.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
index 7dd308129b40f..7c012ad1d7ede 100644
--- a/arch/riscv/kernel/module.c
+++ b/arch/riscv/kernel/module.c
@@ -16,6 +16,10 @@
 #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)
 {
@@ -394,3 +398,15 @@ 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
-- 
2.20.1