Messages in this thread | | | Date | Tue, 26 Oct 2021 14:29:17 -0700 (PDT) | Subject | Re: [PATCH v7 1/3] riscv: Introduce CONFIG_RELOCATABLE | From | Palmer Dabbelt <> |
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On Sat, 09 Oct 2021 10:20:20 PDT (-0700), alex@ghiti.fr wrote: > Arf, I have sent this patchset with the wrong email address. @Palmer > tell me if you want me to resend it correctly.
Sorry for being kind of slow here. It's fine: there's a "From:" in the patch, and git picks those up so it'll match the signed-off-by line. I send pretty much all my patches that way, as I never managed to get my Google address working correctly.
> > Thanks, > > Alex > > On 10/9/21 7:12 PM, Alexandre Ghiti wrote: >> From: Alexandre Ghiti <alex@ghiti.fr> >> >> This config allows to compile 64b kernel as PIE and to relocate it at >> any virtual address at runtime: this paves the way to KASLR. >> Runtime relocation is possible since relocation metadata are embedded into >> the kernel.
IMO this should really be user selectable, at a bare minimum so it's testable. I just sent along a patch to do that (my power's off at home, so email is a bit wacky right now).
I haven't put this on for-next yet as I'm not sure if you had a fix for the kasan issue (which IIUC would conflict with this).
>> Note that relocating at runtime introduces an overhead even if the >> kernel is loaded at the same address it was linked at and that the compiler >> options are those used in arm64 which uses the same RELA relocation >> format. >> >> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr> >> --- >> arch/riscv/Kconfig | 12 ++++++++ >> arch/riscv/Makefile | 7 +++-- >> arch/riscv/kernel/vmlinux.lds.S | 6 ++++ >> arch/riscv/mm/Makefile | 4 +++ >> arch/riscv/mm/init.c | 54 ++++++++++++++++++++++++++++++++- >> 5 files changed, 80 insertions(+), 3 deletions(-) >> >> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig >> index ea16fa2dd768..043ba92559fa 100644 >> --- a/arch/riscv/Kconfig >> +++ b/arch/riscv/Kconfig >> @@ -213,6 +213,18 @@ config PGTABLE_LEVELS >> config LOCKDEP_SUPPORT >> def_bool y >> >> +config RELOCATABLE >> + bool >> + depends on MMU && 64BIT && !XIP_KERNEL >> + help >> + This builds a kernel as a Position Independent Executable (PIE), >> + which retains all relocation metadata required to relocate the >> + kernel binary at runtime to a different virtual address than the >> + address it was linked at. >> + Since RISCV uses the RELA relocation format, this requires a >> + relocation pass at runtime even if the kernel is loaded at the >> + same address it was linked at. >> + >> source "arch/riscv/Kconfig.socs" >> source "arch/riscv/Kconfig.erratas" >> >> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile >> index 0eb4568fbd29..2f509915f246 100644 >> --- a/arch/riscv/Makefile >> +++ b/arch/riscv/Makefile >> @@ -9,9 +9,12 @@ >> # >> >> OBJCOPYFLAGS := -O binary >> -LDFLAGS_vmlinux := >> +ifeq ($(CONFIG_RELOCATABLE),y) >> + LDFLAGS_vmlinux += -shared -Bsymbolic -z notext -z norelro >> + KBUILD_CFLAGS += -fPIE >> +endif >> ifeq ($(CONFIG_DYNAMIC_FTRACE),y) >> - LDFLAGS_vmlinux := --no-relax >> + LDFLAGS_vmlinux += --no-relax >> KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY >> CC_FLAGS_FTRACE := -fpatchable-function-entry=8 >> endif >> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S >> index 5104f3a871e3..862a8c09723c 100644 >> --- a/arch/riscv/kernel/vmlinux.lds.S >> +++ b/arch/riscv/kernel/vmlinux.lds.S >> @@ -133,6 +133,12 @@ SECTIONS >> >> BSS_SECTION(PAGE_SIZE, PAGE_SIZE, 0) >> >> + .rela.dyn : ALIGN(8) { >> + __rela_dyn_start = .; >> + *(.rela .rela*) >> + __rela_dyn_end = .; >> + } >> + >> #ifdef CONFIG_EFI >> . = ALIGN(PECOFF_SECTION_ALIGNMENT); >> __pecoff_data_virt_size = ABSOLUTE(. - __pecoff_text_end); >> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile >> index 7ebaef10ea1b..2d33ec574bbb 100644 >> --- a/arch/riscv/mm/Makefile >> +++ b/arch/riscv/mm/Makefile >> @@ -1,6 +1,10 @@ >> # SPDX-License-Identifier: GPL-2.0-only >> >> CFLAGS_init.o := -mcmodel=medany >> +ifdef CONFIG_RELOCATABLE >> +CFLAGS_init.o += -fno-pie >> +endif >> + >> ifdef CONFIG_FTRACE >> CFLAGS_REMOVE_init.o = $(CC_FLAGS_FTRACE) >> CFLAGS_REMOVE_cacheflush.o = $(CC_FLAGS_FTRACE) >> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c >> index c0cddf0fc22d..42041c12d496 100644 >> --- a/arch/riscv/mm/init.c >> +++ b/arch/riscv/mm/init.c >> @@ -20,6 +20,9 @@ >> #include <linux/dma-map-ops.h> >> #include <linux/crash_dump.h> >> #include <linux/hugetlb.h> >> +#ifdef CONFIG_RELOCATABLE >> +#include <linux/elf.h> >> +#endif >> >> #include <asm/fixmap.h> >> #include <asm/tlbflush.h> >> @@ -103,7 +106,7 @@ static void __init print_vm_layout(void) >> print_mlm("lowmem", (unsigned long)PAGE_OFFSET, >> (unsigned long)high_memory); >> #ifdef CONFIG_64BIT >> - print_mlm("kernel", (unsigned long)KERNEL_LINK_ADDR, >> + print_mlm("kernel", (unsigned long)kernel_map.virt_addr, >> (unsigned long)ADDRESS_SPACE_END); >> #endif >> } >> @@ -518,6 +521,44 @@ static __init pgprot_t pgprot_from_va(uintptr_t va) >> #error "setup_vm() is called from head.S before relocate so it should not use absolute addressing." >> #endif >> >> +#ifdef CONFIG_RELOCATABLE >> +extern unsigned long __rela_dyn_start, __rela_dyn_end; >> + >> +static void __init relocate_kernel(void) >> +{ >> + Elf64_Rela *rela = (Elf64_Rela *)&__rela_dyn_start; >> + /* >> + * This holds the offset between the linked virtual address and the >> + * relocated virtual address. >> + */ >> + uintptr_t reloc_offset = kernel_map.virt_addr - KERNEL_LINK_ADDR; >> + /* >> + * This holds the offset between kernel linked virtual address and >> + * physical address. >> + */ >> + uintptr_t va_kernel_link_pa_offset = KERNEL_LINK_ADDR - kernel_map.phys_addr; >> + >> + for ( ; rela < (Elf64_Rela *)&__rela_dyn_end; rela++) { >> + Elf64_Addr addr = (rela->r_offset - va_kernel_link_pa_offset); >> + Elf64_Addr relocated_addr = rela->r_addend; >> + >> + if (rela->r_info != R_RISCV_RELATIVE) >> + continue; >> + >> + /* >> + * Make sure to not relocate vdso symbols like rt_sigreturn >> + * which are linked from the address 0 in vmlinux since >> + * vdso symbol addresses are actually used as an offset from >> + * mm->context.vdso in VDSO_OFFSET macro. >> + */ >> + if (relocated_addr >= KERNEL_LINK_ADDR) >> + relocated_addr += reloc_offset; >> + >> + *(Elf64_Addr *)addr = relocated_addr; >> + } >> +} >> +#endif /* CONFIG_RELOCATABLE */ >> + >> #ifdef CONFIG_XIP_KERNEL >> static void __init create_kernel_page_table(pgd_t *pgdir, >> __always_unused bool early) >> @@ -625,6 +666,17 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa) >> BUG_ON((kernel_map.virt_addr + kernel_map.size) > ADDRESS_SPACE_END - SZ_4K); >> #endif >> >> +#ifdef CONFIG_RELOCATABLE >> + /* >> + * Early page table uses only one PGDIR, which makes it possible >> + * to map PGDIR_SIZE aligned on PGDIR_SIZE: if the relocation offset >> + * makes the kernel cross over a PGDIR_SIZE boundary, raise a bug >> + * since a part of the kernel would not get mapped. >> + */ >> + BUG_ON(PGDIR_SIZE - (kernel_map.virt_addr & (PGDIR_SIZE - 1)) < kernel_map.size); >> + relocate_kernel(); >> +#endif >> + >> pt_ops.alloc_pte = alloc_pte_early; >> pt_ops.get_pte_virt = get_pte_virt_early; >> #ifndef __PAGETABLE_PMD_FOLDED
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