linux/arch
Ard Biesheuvel 7290d58095 module: use relative references for __ksymtab entries
An ordinary arm64 defconfig build has ~64 KB worth of __ksymtab entries,
each consisting of two 64-bit fields containing absolute references, to
the symbol itself and to a char array containing its name, respectively.

When we build the same configuration with KASLR enabled, we end up with an
additional ~192 KB of relocations in the .init section, i.e., one 24 byte
entry for each absolute reference, which all need to be processed at boot
time.

Given how the struct kernel_symbol that describes each entry is completely
local to module.c (except for the references emitted by EXPORT_SYMBOL()
itself), we can easily modify it to contain two 32-bit relative references
instead.  This reduces the size of the __ksymtab section by 50% for all
64-bit architectures, and gets rid of the runtime relocations entirely for
architectures implementing KASLR, either via standard PIE linking (arm64)
or using custom host tools (x86).

Note that the binary search involving __ksymtab contents relies on each
section being sorted by symbol name.  This is implemented based on the
input section names, not the names in the ksymtab entries, so this patch
does not interfere with that.

Given that the use of place-relative relocations requires support both in
the toolchain and in the module loader, we cannot enable this feature for
all architectures.  So make it dependent on whether
CONFIG_HAVE_ARCH_PREL32_RELOCATIONS is defined.

Link: http://lkml.kernel.org/r/20180704083651.24360-4-ard.biesheuvel@linaro.org
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Jessica Yu <jeyu@kernel.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morris <james.morris@microsoft.com>
Cc: James Morris <jmorris@namei.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Nicolas Pitre <nico@linaro.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Garnier <thgarnie@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-08-22 10:52:47 -07:00
..
alpha mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
arc mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
arm mm: zero out the vma in vma_init() 2018-08-22 10:52:44 -07:00
arm64 arch: enable relative relocations for arm64, power and x86 2018-08-22 10:52:47 -07:00
c6x kconfig: include kernel/Kconfig.preempt from init/Kconfig 2018-08-02 08:06:54 +09:00
h8300 Consolidation of Kconfig files by Christoph Hellwig. 2018-08-15 13:05:12 -07:00
hexagon mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
ia64 Mike Rapoport kindly fixed up ia64 to work with NO_BOOTMEM 2018-08-20 19:37:09 -07:00
m68k Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/gerg/m68knommu 2018-08-19 16:23:03 -07:00
microblaze mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
mips Updates for v4.19: 2018-08-20 18:32:00 -07:00
nds32 mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
nios2 mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
openrisc mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
parisc mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
powerpc arch: enable relative relocations for arm64, power and x86 2018-08-22 10:52:47 -07:00
riscv RISC-V Updates for the 4.19 Merge Window 2018-08-19 09:56:38 -07:00
s390 Updates for v4.19: 2018-08-20 18:32:00 -07:00
sh mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
sparc mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
um mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
unicore32 mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
x86 module: use relative references for __ksymtab entries 2018-08-22 10:52:47 -07:00
xtensa kernel/dma: remove unsupported gfp_mask parameter from dma_alloc_from_contiguous() 2018-08-17 16:20:32 -07:00
.gitignore
Kconfig arch: enable relative relocations for arm64, power and x86 2018-08-22 10:52:47 -07:00