On Mon, Feb 24, 2025 at 10:21 PM Ard Biesheuvel <ardb+git@xxxxxxxxxx> wrote: > > From: Ard Biesheuvel <ardb@xxxxxxxxxx> > > Some architectures build vmlinux with static relocations preserved, but > strip them again from the final vmlinux image. Arch specific tools > consume these static relocations in order to construct relocation tables > for KASLR. > > The fact that vmlinux is created, consumed and subsequently updated goes > against the typical, declarative paradigm used by Make, which is based > on rules and dependencies. So as a first step towards cleaning this up, > introduce a Kconfig symbol to declare that the arch wants to consume the > static relocations emitted into vmlinux. This will be wired up further > in subsequent patches. > > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> I have no objection to this patch. The code diff seems a good clean-up. > --- > Makefile | 4 ++++ > arch/Kconfig | 7 +++++++ > arch/mips/Kconfig | 1 + > arch/mips/Makefile | 4 ---- > arch/riscv/Kconfig | 1 + > arch/riscv/Makefile | 2 +- > arch/s390/Kconfig | 1 + > arch/s390/Makefile | 2 +- > arch/x86/Kconfig | 1 + > arch/x86/Makefile | 6 ------ > 10 files changed, 17 insertions(+), 12 deletions(-) > > diff --git a/Makefile b/Makefile > index 30dab4c8b012..a3302dce56de 100644 > --- a/Makefile > +++ b/Makefile > @@ -1119,6 +1119,10 @@ ifdef CONFIG_LD_ORPHAN_WARN > LDFLAGS_vmlinux += --orphan-handling=$(CONFIG_LD_ORPHAN_WARN_LEVEL) > endif > > +ifneq ($(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS),) > +LDFLAGS_vmlinux += --emit-relocs --discard-none > +endif > + > # Align the bit size of userspace programs with the kernel > KBUILD_USERCFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS)) > KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS)) > diff --git a/arch/Kconfig b/arch/Kconfig > index b8a4ff365582..101a13fcde8e 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -1695,6 +1695,13 @@ config ARCH_HAS_KERNEL_FPU_SUPPORT > Architectures that select this option can run floating-point code in > the kernel, as described in Documentation/core-api/floating-point.rst. > > +config ARCH_VMLINUX_NEEDS_RELOCS > + bool > + help > + Whether the architecture needs vmlinux to be built with static > + relocations preserved. This is used by some architectures to > + construct bespoke relocation tables for KASLR. > + > source "kernel/gcov/Kconfig" > > source "scripts/gcc-plugins/Kconfig" > diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig > index 1924f2d83932..5aedbd7afadb 100644 > --- a/arch/mips/Kconfig > +++ b/arch/mips/Kconfig > @@ -2617,6 +2617,7 @@ config RELOCATABLE > CPU_MIPS32_R6 || CPU_MIPS64_R6 || \ > CPU_P5600 || CAVIUM_OCTEON_SOC || \ > CPU_LOONGSON64 > + select ARCH_VMLINUX_NEEDS_RELOCS > help > This builds a kernel image that retains relocation information > so it can be loaded someplace besides the default 1MB. > diff --git a/arch/mips/Makefile b/arch/mips/Makefile > index be8cb44a89fd..d9057e29bc62 100644 > --- a/arch/mips/Makefile > +++ b/arch/mips/Makefile > @@ -100,10 +100,6 @@ LDFLAGS_vmlinux += -G 0 -static -n -nostdlib > KBUILD_AFLAGS_MODULE += -mlong-calls > KBUILD_CFLAGS_MODULE += -mlong-calls > > -ifeq ($(CONFIG_RELOCATABLE),y) > -LDFLAGS_vmlinux += --emit-relocs > -endif > - > cflags-y += -ffreestanding > > cflags-$(CONFIG_CPU_BIG_ENDIAN) += -EB > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > index 7612c52e9b1e..6f5800114416 100644 > --- a/arch/riscv/Kconfig > +++ b/arch/riscv/Kconfig > @@ -1077,6 +1077,7 @@ config RELOCATABLE > bool "Build a relocatable kernel" > depends on MMU && 64BIT && !XIP_KERNEL > select MODULE_SECTIONS if MODULES > + select ARCH_VMLINUX_NEEDS_RELOCS > help > This builds a kernel as a Position Independent Executable (PIE), > which retains all relocation metadata required to relocate the > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile > index 13fbc0f94238..6ef0d10e0c50 100644 > --- a/arch/riscv/Makefile > +++ b/arch/riscv/Makefile > @@ -8,7 +8,7 @@ > > LDFLAGS_vmlinux := -z norelro > ifeq ($(CONFIG_RELOCATABLE),y) > - LDFLAGS_vmlinux += -shared -Bsymbolic -z notext --emit-relocs > + LDFLAGS_vmlinux += -shared -Bsymbolic -z notext > KBUILD_CFLAGS += -fPIE > endif > ifeq ($(CONFIG_DYNAMIC_FTRACE),y) > diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig > index 9c9ec08d78c7..ea67b7317138 100644 > --- a/arch/s390/Kconfig > +++ b/arch/s390/Kconfig > @@ -630,6 +630,7 @@ endchoice > > config RELOCATABLE > def_bool y > + select ARCH_VMLINUX_NEEDS_RELOCS > help > This builds a kernel image that retains relocation information > so it can be loaded at an arbitrary address. > diff --git a/arch/s390/Makefile b/arch/s390/Makefile > index 5fae311203c2..d5f4be440879 100644 > --- a/arch/s390/Makefile > +++ b/arch/s390/Makefile > @@ -15,7 +15,7 @@ KBUILD_CFLAGS_MODULE += -fPIC > KBUILD_AFLAGS += -m64 > KBUILD_CFLAGS += -m64 > KBUILD_CFLAGS += -fPIC > -LDFLAGS_vmlinux := -no-pie --emit-relocs --discard-none > +LDFLAGS_vmlinux := -no-pie > extra_tools := relocs > aflags_dwarf := -Wa,-gdwarf-2 > KBUILD_AFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -D__ASSEMBLY__ > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index be2c311f5118..2005d80ff8d1 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -2199,6 +2199,7 @@ config RANDOMIZE_BASE > config X86_NEED_RELOCS > def_bool y > depends on RANDOMIZE_BASE || (X86_32 && RELOCATABLE) > + select ARCH_VMLINUX_NEEDS_RELOCS > > config PHYSICAL_ALIGN > hex "Alignment value to which kernel should be aligned" > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > index 5b773b34768d..f65ed6dcd6fb 100644 > --- a/arch/x86/Makefile > +++ b/arch/x86/Makefile > @@ -251,12 +251,6 @@ endif > > KBUILD_LDFLAGS += -m elf_$(UTS_MACHINE) > > -ifdef CONFIG_X86_NEED_RELOCS > -LDFLAGS_vmlinux := --emit-relocs --discard-none > -else > -LDFLAGS_vmlinux := > -endif > - > # > # The 64-bit kernel must be aligned to 2MB. Pass -z max-page-size=0x200000 to > # the linker to force 2MB page size regardless of the default page size used > -- > 2.48.1.601.g30ceb7b040-goog > > -- Best Regards Masahiro Yamada
