Re: [PATCH] riscv: Introduce CONFIG_RELOCATABLE

From: Anup Patel
Date: Wed Jan 29 2020 - 23:39:38 EST

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On Thu, Jan 30, 2020 at 9:44 AM Zong Li <zong.li@xxxxxxxxxx> wrote:
>
> On Fri, Jan 24, 2020 at 4:14 AM Alexandre Ghiti <alex@xxxxxxxx> 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@xxxxxxxx>
> > ---
> > arch/riscv/Kconfig | 11 ++++
> > 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, 110 insertions(+), 22 deletions(-)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index fa7dc03459e7..c652b4b850ce 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -163,6 +163,17 @@ config PGTABLE_LEVELS
> > default 3 if 64BIT
> > default 2
> >
> > +config RELOCATABLE
> > + bool
> > + 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 ac699246ae7e..27c95da68ecb 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_load_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_load_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 2227db63f895..5042b2b48a06 100644
> > --- a/arch/riscv/kernel/head.S
> > +++ b/arch/riscv/kernel/head.S
> > @@ -126,7 +126,8 @@ clear_bss_done:
> > #ifdef CONFIG_MMU
> > relocate:
> > /* Relocate return address */
> > - li a1, PAGE_OFFSET
> > + la a1, kernel_load_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 12f42f96d46e..5095aee7c37e 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>
> > @@ -70,9 +70,11 @@ 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 a1bd95c8047a..dcd3d806243f 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..ac9a9f69abc0 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_load_addr = _AC(CONFIG_PAGE_OFFSET, UL);
> > +EXPORT_SYMBOL(kernel_load_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_load_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_load_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_load_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_load_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_load_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_load_addr,
> > (uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE);
> > - create_pmd_mapping(trampoline_pmd, PAGE_OFFSET,
> > + create_pmd_mapping(trampoline_pmd, kernel_load_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_load_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_load_addr + load_sz;
> > + for (va = kernel_load_addr; va < end_va; va += map_size)
> > create_pgd_mapping(early_pg_dir, va,
> > - load_pa + (va - PAGE_OFFSET),
> > + load_pa + (va - kernel_load_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(kernel_load_addr) &&
> > + __pa(kernel_load_addr) < end)
> > + start = __pa(kernel_load_addr);
>
> Here should use __pa_symbol() instead of __pa() for kernel symbols.
>
> I'm working on KASLR on top of this patch, it's work to me.
>
> Reviewed-by: Zong Li <zong.li@xxxxxxxxxx>
> Tested-by: Zong Li <zong.li@xxxxxxxxxx>

Thanks for testing. I will not test since you already tested it.

Regards,
Anup

>
> >
> > map_size = best_map_size(start, end - start);
> > for (pa = start; pa < end; pa += map_size) {
> > --
> > 2.20.1
> >

Next message: Dmitry Osipenko: "[PATCH v6 01/16] dmaengine: tegra-apb: Fix use-after-free"
Previous message: Oder Chiou: "RE: [PATCH] ASoC: rt5659: add S32_LE format"
In reply to: Zong Li: "Re: [PATCH] riscv: Introduce CONFIG_RELOCATABLE"
Next in thread: Alex Ghiti: "Re: [PATCH] riscv: Introduce CONFIG_RELOCATABLE"
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