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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F0374C433F5 for ; Sat, 9 Oct 2021 22:16:28 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C06E360F39 for ; Sat, 9 Oct 2021 22:16:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org C06E360F39 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=canonical.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4HRfXn6Gdrz305P for ; Sun, 10 Oct 2021 09:16:25 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=fail (SPF fail - not authorized) smtp.mailfrom=canonical.com (client-ip=217.70.183.197; helo=relay5-d.mail.gandi.net; envelope-from=alexandre.ghiti@canonical.com; receiver=) X-Greylist: delayed 64 seconds by postgrey-1.36 at boromir; Sun, 10 Oct 2021 04:14:26 AEDT Received: from relay5-d.mail.gandi.net (relay5-d.mail.gandi.net [217.70.183.197]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4HRWrL4gXvz2yMH for ; Sun, 10 Oct 2021 04:14:26 +1100 (AEDT) Received: (Authenticated sender: alex@ghiti.fr) by relay5-d.mail.gandi.net (Postfix) with ESMTPSA id 1B6F01C0004; Sat, 9 Oct 2021 17:14:16 +0000 (UTC) From: Alexandre Ghiti To: Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Paul Walmsley , Palmer Dabbelt , Albert Ou , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Subject: [PATCH v7 1/3] riscv: Introduce CONFIG_RELOCATABLE Date: Sat, 9 Oct 2021 19:12:57 +0200 Message-Id: <20211009171259.2515351-2-alexandre.ghiti@canonical.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20211009171259.2515351-1-alexandre.ghiti@canonical.com> References: <20211009171259.2515351-1-alexandre.ghiti@canonical.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Mailman-Approved-At: Sun, 10 Oct 2021 09:16:02 +1100 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Alexandre Ghiti Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" From: Alexandre Ghiti 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. 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 --- 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 #include #include +#ifdef CONFIG_RELOCATABLE +#include +#endif #include #include @@ -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 -- 2.30.2