Messages in this thread | | | From | Anup Patel <> | Date | Sat, 29 Feb 2020 19:01:39 +0530 | Subject | Re: [PATCH v2] riscv: Introduce CONFIG_RELOCATABLE |
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On Sat, Feb 29, 2020 at 6:14 PM Alexandre Ghiti <alex@ghiti.fr> wrote: > > This config allows to compile the kernel as PIE and to relocate it at any > virtual address at runtime: this paves the way to KASLR and to 4-level > page table folding at runtime. Runtime relocation is possible since > relocation metadata are embedded into the kernel. > > 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> > Reviewed-by: Zong Li <zong.li@sifive.com> > Tested-by: Zong Li <zong.li@sifive.com>
LGTM.
Reviewed-by: Anup Patel <anup@brainfault.org>
Regards, Anup
> --- > Changes in v2: > - Make RELOCATABLE depend on MMU as suggested by Anup > - Rename kernel_load_addr into kernel_virt_addr as suggested by Anup > - Use __pa_symbol instead of __pa, as suggested by Zong > - Rebased on top of v5.6-rc3 > - Tested with sv48 patchset > - Add Reviewed/Tested-by from Zong > > arch/riscv/Kconfig | 12 +++++ > arch/riscv/Makefile | 5 +- > arch/riscv/boot/loader.lds.S | 2 +- > arch/riscv/include/asm/page.h | 5 +- > arch/riscv/kernel/head.S | 3 +- > arch/riscv/kernel/vmlinux.lds.S | 10 ++-- > arch/riscv/mm/Makefile | 4 ++ > arch/riscv/mm/init.c | 92 ++++++++++++++++++++++++++++----- > 8 files changed, 111 insertions(+), 22 deletions(-) > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > index 73f029eae0cc..f5f3d474504d 100644 > --- a/arch/riscv/Kconfig > +++ b/arch/riscv/Kconfig > @@ -163,6 +163,18 @@ config PGTABLE_LEVELS > default 3 if 64BIT > default 2 > > +config RELOCATABLE > + bool > + depends on MMU > + 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" > > menu "Platform type" > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile > index b9009a2fbaf5..5a115cf6a9c1 100644 > --- a/arch/riscv/Makefile > +++ b/arch/riscv/Makefile > @@ -9,7 +9,10 @@ > # > > 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 > endif > diff --git a/arch/riscv/boot/loader.lds.S b/arch/riscv/boot/loader.lds.S > index 47a5003c2e28..a9ed218171aa 100644 > --- a/arch/riscv/boot/loader.lds.S > +++ b/arch/riscv/boot/loader.lds.S > @@ -7,7 +7,7 @@ ENTRY(_start) > > SECTIONS > { > - . = PAGE_OFFSET; > + . = CONFIG_PAGE_OFFSET; > > .payload : { > *(.payload) > diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h > index 8ca1930caa44..af5810f9aebd 100644 > --- a/arch/riscv/include/asm/page.h > +++ b/arch/riscv/include/asm/page.h > @@ -31,9 +31,9 @@ > * When not using MMU this corresponds to the first free page in > * physical memory (aligned on a page boundary). > */ > -#define PAGE_OFFSET _AC(CONFIG_PAGE_OFFSET, UL) > +#define PAGE_OFFSET kernel_virt_addr > > -#define KERN_VIRT_SIZE (-PAGE_OFFSET) > +#define KERN_VIRT_SIZE (-_AC(CONFIG_PAGE_OFFSET, UL)) > > #ifndef __ASSEMBLY__ > > @@ -97,6 +97,7 @@ extern unsigned long pfn_base; > #define ARCH_PFN_OFFSET (PAGE_OFFSET >> PAGE_SHIFT) > #endif /* CONFIG_MMU */ > > +extern unsigned long kernel_virt_addr; > extern unsigned long max_low_pfn; > extern unsigned long min_low_pfn; > > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S > index 271860fc2c3f..d792912c2da3 100644 > --- a/arch/riscv/kernel/head.S > +++ b/arch/riscv/kernel/head.S > @@ -131,7 +131,8 @@ clear_bss_done: > #ifdef CONFIG_MMU > relocate: > /* Relocate return address */ > - li a1, PAGE_OFFSET > + la a1, kernel_virt_addr > + REG_L a1, 0(a1) > la a2, _start > sub a1, a1, a2 > add ra, ra, a1 > diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S > index 1e0193ded420..5bf69e9b91e6 100644 > --- a/arch/riscv/kernel/vmlinux.lds.S > +++ b/arch/riscv/kernel/vmlinux.lds.S > @@ -4,7 +4,7 @@ > * Copyright (C) 2017 SiFive > */ > > -#define LOAD_OFFSET PAGE_OFFSET > +#define LOAD_OFFSET CONFIG_PAGE_OFFSET > #include <asm/vmlinux.lds.h> > #include <asm/page.h> > #include <asm/cache.h> > @@ -71,9 +71,11 @@ SECTIONS > > EXCEPTION_TABLE(0x10) > > - .rel.dyn : { > - *(.rel.dyn*) > - } > + .rela.dyn : ALIGN(8) { > + __rela_dyn_start = .; > + *(.rela .rela*) > + __rela_dyn_end = .; > + } > > _end = .; > > diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile > index 50b7af58c566..27593d362248 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 = -pg > endif > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c > index 965a8cf4829c..428aee2669aa 100644 > --- a/arch/riscv/mm/init.c > +++ b/arch/riscv/mm/init.c > @@ -12,6 +12,9 @@ > #include <linux/sizes.h> > #include <linux/of_fdt.h> > #include <linux/libfdt.h> > +#ifdef CONFIG_RELOCATABLE > +#include <linux/elf.h> > +#endif > > #include <asm/fixmap.h> > #include <asm/tlbflush.h> > @@ -28,6 +31,9 @@ EXPORT_SYMBOL(empty_zero_page); > extern char _start[]; > void *dtb_early_va; > > +unsigned long kernel_virt_addr = _AC(CONFIG_PAGE_OFFSET, UL); > +EXPORT_SYMBOL(kernel_virt_addr); > + > static void __init zone_sizes_init(void) > { > unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, }; > @@ -132,7 +138,8 @@ void __init setup_bootmem(void) > phys_addr_t end = reg->base + reg->size; > > if (reg->base <= vmlinux_end && vmlinux_end <= end) { > - mem_size = min(reg->size, (phys_addr_t)-PAGE_OFFSET); > + mem_size = min(reg->size, > + (phys_addr_t)-kernel_virt_addr); > > /* > * Remove memblock from the end of usable area to the > @@ -269,7 +276,7 @@ static phys_addr_t __init alloc_pmd(uintptr_t va) > if (mmu_enabled) > return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE); > > - pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT; > + pmd_num = (va - kernel_virt_addr) >> PGDIR_SHIFT; > BUG_ON(pmd_num >= NUM_EARLY_PMDS); > return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD]; > } > @@ -370,6 +377,54 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size) > #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; > + > +#ifdef CONFIG_64BIT > +#define Elf_Rela Elf64_Rela > +#define Elf_Addr Elf64_Addr > +#else > +#define Elf_Rela Elf32_Rela > +#define Elf_Addr Elf32_Addr > +#endif > + > +void __init relocate_kernel(uintptr_t load_pa) > +{ > + Elf_Rela *rela = (Elf_Rela *)&__rela_dyn_start; > + uintptr_t link_addr = _AC(CONFIG_PAGE_OFFSET, UL); > + /* > + * This holds the offset between the linked virtual address and the > + * relocated virtual address. > + */ > + uintptr_t reloc_offset = kernel_virt_addr - link_addr; > + /* > + * This holds the offset between linked virtual address and physical > + * address whereas va_pa_offset holds the offset between relocated > + * virtual address and physical address. > + */ > + uintptr_t va_link_pa_offset = link_addr - load_pa; > + > + for ( ; rela < (Elf_Rela *)&__rela_dyn_end; rela++) { > + Elf_Addr addr = (rela->r_offset - va_link_pa_offset); > + Elf_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 >= link_addr) > + relocated_addr += reloc_offset; > + > + *(Elf_Addr *)addr = relocated_addr; > + } > +} > +#endif > + > asmlinkage void __init setup_vm(uintptr_t dtb_pa) > { > uintptr_t va, end_va; > @@ -377,9 +432,20 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa) > uintptr_t load_sz = (uintptr_t)(&_end) - load_pa; > uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE); > > - va_pa_offset = PAGE_OFFSET - load_pa; > + va_pa_offset = kernel_virt_addr - load_pa; > pfn_base = PFN_DOWN(load_pa); > > +#ifdef CONFIG_RELOCATABLE > + /* > + * Early page table uses only one PGDIR, which makes it possible > + * to map 1GB aligned on 1GB: if the relocation offset makes the kernel > + * cross over a 1G boundary, raise a bug since a part of the kernel > + * would not get mapped. > + */ > + BUG_ON(SZ_1G - (kernel_virt_addr & (SZ_1G - 1)) < load_sz); > + relocate_kernel(load_pa); > +#endif > + > /* > * Enforce boot alignment requirements of RV32 and > * RV64 by only allowing PMD or PGD mappings. > @@ -387,7 +453,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa) > BUG_ON(map_size == PAGE_SIZE); > > /* Sanity check alignment and size */ > - BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0); > + BUILD_BUG_ON((_AC(CONFIG_PAGE_OFFSET, UL) % PGDIR_SIZE) != 0); > BUG_ON((load_pa % map_size) != 0); > BUG_ON(load_sz > MAX_EARLY_MAPPING_SIZE); > > @@ -400,13 +466,13 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa) > create_pmd_mapping(fixmap_pmd, FIXADDR_START, > (uintptr_t)fixmap_pte, PMD_SIZE, PAGE_TABLE); > /* Setup trampoline PGD and PMD */ > - create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET, > + create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr, > (uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE); > - create_pmd_mapping(trampoline_pmd, PAGE_OFFSET, > + create_pmd_mapping(trampoline_pmd, kernel_virt_addr, > load_pa, PMD_SIZE, PAGE_KERNEL_EXEC); > #else > /* Setup trampoline PGD */ > - create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET, > + create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr, > load_pa, PGDIR_SIZE, PAGE_KERNEL_EXEC); > #endif > > @@ -415,10 +481,10 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa) > * us to reach paging_init(). We map all memory banks later > * in setup_vm_final() below. > */ > - end_va = PAGE_OFFSET + load_sz; > - for (va = PAGE_OFFSET; va < end_va; va += map_size) > + end_va = kernel_virt_addr + load_sz; > + for (va = kernel_virt_addr; va < end_va; va += map_size) > create_pgd_mapping(early_pg_dir, va, > - load_pa + (va - PAGE_OFFSET), > + load_pa + (va - kernel_virt_addr), > map_size, PAGE_KERNEL_EXEC); > > /* Create fixed mapping for early FDT parsing */ > @@ -457,9 +523,9 @@ static void __init setup_vm_final(void) > break; > if (memblock_is_nomap(reg)) > continue; > - if (start <= __pa(PAGE_OFFSET) && > - __pa(PAGE_OFFSET) < end) > - start = __pa(PAGE_OFFSET); > + if (start <= __pa_symbol(kernel_virt_addr) && > + __pa(kernel_virt_addr) < end) > + start = __pa_symbol(kernel_virt_addr); > > map_size = best_map_size(start, end - start); > for (pa = start; pa < end; pa += map_size) { > -- > 2.20.1 >
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