From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0DE5AC4332D for ; Sun, 22 Mar 2020 07:11:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C73E020719 for ; Sun, 22 Mar 2020 07:11:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726137AbgCVHKt (ORCPT ); Sun, 22 Mar 2020 03:10:49 -0400 Received: from relay9-d.mail.gandi.net ([217.70.183.199]:42911 "EHLO relay9-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725769AbgCVHKt (ORCPT ); Sun, 22 Mar 2020 03:10:49 -0400 X-Originating-IP: 2.7.45.25 Received: from [192.168.1.11] (lfbn-lyo-1-453-25.w2-7.abo.wanadoo.fr [2.7.45.25]) (Authenticated sender: alex@ghiti.fr) by relay9-d.mail.gandi.net (Postfix) with ESMTPSA id 7FDBFFF802; Sun, 22 Mar 2020 07:10:45 +0000 (UTC) From: Alex Ghiti Subject: Re: [PATCH RESEND v2] riscv: Introduce CONFIG_RELOCATABLE To: Zong Li , Palmer Dabbelt Cc: Paul Walmsley , Anup Patel , linux-riscv , "linux-kernel@vger.kernel.org List" References: <20200303054437.650-1-alex@ghiti.fr> Message-ID: <4d8f0629-4815-825f-fda2-3033e7956da3@ghiti.fr> Date: Sun, 22 Mar 2020 03:10:45 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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 >>> Reviewed-by: Zong Li >>> Reviewed-by: Anup Patel >>> Tested-by: Zong Li >>> --- >>> 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. Is there any issue with having PAGE_OFFSET equal to kernel_virt_addr ? 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. > >>> -#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 >>> #include >>> #include >>> @@ -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 >>> #include >>> #include >>> +#ifdef CONFIG_RELOCATABLE >>> +#include >>> +#endif >>> >>> #include >>> #include >>> @@ -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