Messages in this thread | | | From | Alex Ghiti <> | Subject | Re: [PATCH RESEND v2] riscv: Introduce CONFIG_RELOCATABLE | Date | Sun, 29 Mar 2020 12:15:08 -0400 |
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Hi Zong,
On 3/24/20 3:22 AM, Zong Li wrote: > On Sun, Mar 22, 2020 at 3:10 PM Alex Ghiti <alex@ghiti.fr> wrote: >> >> Hi Zong, >> >> Sorry for the response delay, please find below my comments. >> >> On 3/12/20 1:57 AM, Zong Li wrote: >>> On Sat, Mar 7, 2020 at 1:58 AM Palmer Dabbelt <palmer@dabbelt.com> wrote: >>>> >>>> On Mon, 02 Mar 2020 21:44:37 PST (-0800), 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> >>>>> Reviewed-by: Anup Patel <anup@brainfault.org> >>>>> Tested-by: Zong Li <zong.li@sifive.com> >>>>> --- >>>>> 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 and Anup >>>>> >>>>> 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 >>>> >>>> I assume we want to keep PAGE_OFFSET a constant for the non-relocatable >>>> systems. As it currently stands this is imposing a performance hit even when >>>> >>> >>> I had almost done the KASLR implementation on top of this patch. >>> Actually, PAGE_OFFSET change is unnecessary in KASLR , because we >>> would move kernel image to a random physical address as well, so the >>> $pc will go to the relevant random virtual address. We need >> >> I don't understand what you mean here, can you explain it a bit more ? >> >>> kernel_virt_addr to record the new destination, but keep PAGE_OFFSET >>> to be CONFIG_PAGE_OFFSET is enough. >> >> From my understanding, PAGE_OFFSET should represent the start of the >> direct mapping, so in case of a relocatable kernel, its value should >> reflect the offset too. >> > > Let me try to use the common RISC-V case to explain that. > > In this v2 version, we could use a random virtual address to map the > kernel image which is located in 0x8020_0000 physical address, then we > could achieve the purpose of randomization, but it only happens on > virtual address, the kernel image is still in 0x8020_0000 physical > address, so we would also try to move the physical location of kernel > image by a random offset. > > For example, assume there is a 1G size DDR, the kernel image size is > 10MB and we get a random kernel offset 0x100_0000, finally, kernel > image would locate in 0x8120_0000, and run on corresponding virtual > address 0xffff_ffe0_0100_0000 in CPU view. The direct mapping range is > still got from 0x8020_0000 to 0xc000_0000, that means, there are > available free pages from 0x8020_0000 to 0x811f_ffff, and a reserved > region for kernel image from 0x8120_0000 to 0x81c0_0000, the rest of > the memory are free pages as well (in fact, there are other reserved > regions such as dtb, initrd and so on). Hence, we don't change > PAGE_OFFSET, the PAGE_OFFSET still represent the start of the direct > mapping as you mentioned, but the location of kernel image which in > direct mapping would be unpredictable. > >> Is there any issue with having PAGE_OFFSET equal to kernel_virt_addr ? > > If we make PAGE_OFFSET be the new random kernel start address, the > system would lose the part of memory after we also moving kernel image > to a new physical location, that means, the memory which prior of new > random kernel start address is disappeared, because some reasons like > it only creates page table start from new physical address, the > memblock only sees the memory from __pa(PAGE_OFFSET), and etc. > >> >> If we use both, we will need to know precisely when we should use >> kernel_virt_addr or PAGE_OFFSET, which I think will be painful and error >> prone. > > There is a use case, we could get kernel offset by the expression > 'kernel_virt_addr - PAGE_OFFSET'. > > It seems to me that I could post the RFC patches first, but it depends > on other patch series, include your relocation implementation. >
You are totally right, thanks for your explanation. I'll fix that in v3 then.
I'll take a look at your KASLR implementation soon,
Thanks,
Alex
>> >>> >>>>> -#define KERN_VIRT_SIZE (-PAGE_OFFSET) >>>>> +#define KERN_VIRT_SIZE (-_AC(CONFIG_PAGE_OFFSET, UL)) >>>> >>>> This seems like it would cause issues if the kernel is relocated to high enough >>>> addresses that "kernel_virt_addr+KERN_VIRT_SIZE" overflows. >>>> >>> >>> Based on the same reason, keep KERN_VIRT_SIZE to be -PAGE_OFFSET is good. >>> >>>>> #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 = .; >>>>> + } >>>> >>>> It looks like the indentation is screwed up here: I see a mix of tabs/spaces >>>> that doesn't match the rest of the file. >>>> >>>>> >>>>> _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); >>>> >>>> PAGE_OFFSET is kernel_virt_addr, so I don't see any reason to change these -- >>>> they account for a significant fraction of the diff. >>>> >>> >>> kernel_virt_addr would be assigned to a random destination by KASLR, >>> but here still should be PAGE_OFFSET rather than kernel_virt_addr as >>> mentioned above. >>> >>>>> /* >>>>> * 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; >>> >>> Here is the same, please use PAGE_OFFSET instead of kernel_virt_addr. >>> >>>>> 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; >>>> >>>> This should at least provide a warning when it encounters an unresolvable >>>> relocation. Is it currently stands this just ignores all other runtime >>>> relocations, and while I can buy the argument there shouldn't be any (though >>>> I'd expect R_RISCV_{32,64} to show up?) we certainly shouldn't just silently >>>> skip them. >>>> >>>>> + >>>>> + /* >>>>> + * 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); >>> >>> Here is the same, please use PAGE_OFFSET instead of kernel_virt_addr. >>> >>>>> >>>>> map_size = best_map_size(start, end - start); >>>>> for (pa = start; pa < end; pa += map_size) { >> >> Thanks, >> >> Alex
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