[PATCH v6 22/27] x86/modules: Add option to start module section after kernel

[Thomas Garnier <thgarnie@chromium.org>]

Add an option so the module section is just after the mapped kernel. It
will ensure position independent modules are always at the right
distance from the kernel and do not require mcmodule=large. It also
optimize the available size for modules by getting rid of the empty
space on kernel randomization range.

Signed-off-by: Thomas Garnier <thgarnie@chromium.org>
---
 Documentation/x86/x86_64/mm.txt         | 3 +++
 arch/x86/Kconfig                        | 4 ++++
 arch/x86/include/asm/pgtable_64_types.h | 6 ++++++
 arch/x86/kernel/head64.c                | 5 ++++-
 arch/x86/mm/dump_pagetables.c           | 3 ++-
 5 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/Documentation/x86/x86_64/mm.txt b/Documentation/x86/x86_64/mm.txt
index 804f9426ed17..35b845d695d5 100644
--- a/Documentation/x86/x86_64/mm.txt
+++ b/Documentation/x86/x86_64/mm.txt
@@ -151,3 +151,6 @@ correct as KASAN disables KASLR.
 
 For both 4- and 5-level layouts, the STACKLEAK_POISON value in the last 2MB
 hole: ffffffffffff4111
+
+If CONFIG_DYNAMIC_MODULE_BASE is enabled, the module section follows the end of
+the mapped kernel.
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 263d81c570b2..c3ad1b0ae1a1 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2221,6 +2221,10 @@ config RANDOMIZE_MEMORY_PHYSICAL_PADDING
 
 	   If unsure, leave at the default value.
 
+# Module section starts just after the end of the kernel module
+config DYNAMIC_MODULE_BASE
+	bool
+
 config X86_GLOBAL_STACKPROTECTOR
 	bool "Stack cookie using a global variable"
 	depends on CC_STACKPROTECTOR_AUTO
diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
index 88bca456da99..d1bb676ec376 100644
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h
@@ -7,6 +7,7 @@
 #ifndef __ASSEMBLY__
 #include <linux/types.h>
 #include <asm/kaslr.h>
+#include <asm/sections.h>
 
 /*
  * These are used to make use of C type-checking..
@@ -141,7 +142,12 @@ extern unsigned int ptrs_per_p4d;
 
 #define VMALLOC_END		(VMALLOC_START + (VMALLOC_SIZE_TB << 40) - 1)
 
+#ifdef CONFIG_DYNAMIC_MODULE_BASE
+#define MODULES_VADDR		ALIGN(((unsigned long)_end + PAGE_SIZE), PMD_SIZE)
+#else
 #define MODULES_VADDR		(__START_KERNEL_map + KERNEL_IMAGE_SIZE)
+#endif
+
 /* The module sections ends with the start of the fixmap */
 #define MODULES_END		_AC(0xffffffffff000000, UL)
 #define MODULES_LEN		(MODULES_END - MODULES_VADDR)
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 22e81275495b..ca2f6ff431af 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -411,12 +411,15 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
 	 * Build-time sanity checks on the kernel image and module
 	 * area mappings. (these are purely build-time and produce no code)
 	 */
+#ifndef CONFIG_DYNAMIC_MODULE_BASE
 	BUILD_BUG_ON(MODULES_VADDR < __START_KERNEL_map);
 	BUILD_BUG_ON(MODULES_VADDR - __START_KERNEL_map < KERNEL_IMAGE_SIZE);
-	BUILD_BUG_ON(MODULES_LEN + KERNEL_IMAGE_SIZE > 2*PUD_SIZE);
+	BUILD_BUG_ON(!IS_ENABLED(CONFIG_RANDOMIZE_BASE_LARGE) &&
+		     MODULES_LEN + KERNEL_IMAGE_SIZE > 2*PUD_SIZE);
 	BUILD_BUG_ON((__START_KERNEL_map & ~PMD_MASK) != 0);
 	BUILD_BUG_ON((MODULES_VADDR & ~PMD_MASK) != 0);
 	BUILD_BUG_ON(!(MODULES_VADDR > __START_KERNEL));
+#endif
 	MAYBE_BUILD_BUG_ON(!(((MODULES_END - 1) & PGDIR_MASK) ==
 				(__START_KERNEL & PGDIR_MASK)));
 	BUILD_BUG_ON(__fix_to_virt(__end_of_fixed_addresses) <= MODULES_END);
diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index e3cdc85ce5b6..3172bd968215 100644
--- a/arch/x86/mm/dump_pagetables.c
+++ b/arch/x86/mm/dump_pagetables.c
@@ -104,7 +104,7 @@ static struct addr_marker address_markers[] = {
 	[EFI_END_NR]		= { EFI_VA_END,		"EFI Runtime Services" },
 #endif
 	[HIGH_KERNEL_NR]	= { __START_KERNEL_map,	"High Kernel Mapping" },
-	[MODULES_VADDR_NR]	= { MODULES_VADDR,	"Modules" },
+	[MODULES_VADDR_NR]	= { 0/*MODULES_VADDR*/,	"Modules" },
 	[MODULES_END_NR]	= { MODULES_END,	"End Modules" },
 	[FIXADDR_START_NR]	= { FIXADDR_START,	"Fixmap Area" },
 	[END_OF_SPACE_NR]	= { -1,			NULL }
@@ -623,6 +623,7 @@ static int __init pt_dump_init(void)
 	address_markers[KASAN_SHADOW_START_NR].start_address = KASAN_SHADOW_START;
 	address_markers[KASAN_SHADOW_END_NR].start_address = KASAN_SHADOW_END;
 #endif
+	address_markers[MODULES_VADDR_NR].start_address = MODULES_VADDR;
 #endif
 #ifdef CONFIG_X86_32
 	address_markers[VMALLOC_START_NR].start_address = VMALLOC_START;
-- 
2.20.1.495.gaa96b0ce6b-goog