Messages in this thread | | | Subject | Re: [PATCH RFC 6/8] riscv/kaslr: clear the original kernel image | From | Alex Ghiti <> | Date | Thu, 9 Apr 2020 01:53:12 -0400 |
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On 4/7/20 7:18 AM, Zong Li wrote: > On Tue, Apr 7, 2020 at 1:11 PM Alex Ghiti <alex@ghiti.fr> wrote: >> >> On 3/24/20 3:30 AM, Zong Li wrote: >>> After completing final page table, we can clear original kernel image >>> and remove executable permission. >>> >>> Signed-off-by: Zong Li <zong.li@sifive.com> >>> --- >>> arch/riscv/include/asm/kaslr.h | 12 ++++++++++++ >>> arch/riscv/kernel/kaslr.c | 12 ++++++++++++ >>> arch/riscv/mm/init.c | 6 ++++++ >>> 3 files changed, 30 insertions(+) >>> create mode 100644 arch/riscv/include/asm/kaslr.h >>> >>> diff --git a/arch/riscv/include/asm/kaslr.h b/arch/riscv/include/asm/kaslr.h >>> new file mode 100644 >>> index 000000000000..b165fe71dd4a >>> --- /dev/null >>> +++ b/arch/riscv/include/asm/kaslr.h >>> @@ -0,0 +1,12 @@ >>> +/* SPDX-License-Identifier: GPL-2.0-only */ >>> +/* >>> + * Copyright (C) 2020 SiFive >>> + * Copyright (C) 2020 Zong Li <zong.li@sifive.com> >>> + */ >>> + >>> +#ifndef _ASM_RISCV_KASLR_H >>> +#define _ASM_RISCV_KASLR_H >>> + >>> +void __init kaslr_late_init(void); >>> + >>> +#endif /* _ASM_RISCV_KASLR_H */ >>> diff --git a/arch/riscv/kernel/kaslr.c b/arch/riscv/kernel/kaslr.c >>> index 59001d6fdfc3..0bd30831c455 100644 >>> --- a/arch/riscv/kernel/kaslr.c >>> +++ b/arch/riscv/kernel/kaslr.c >>> @@ -356,6 +356,18 @@ static __init uintptr_t get_random_offset(u64 seed, uintptr_t kernel_size) >>> return get_legal_offset(random, kernel_size_align); >>> } >>> >>> +void __init kaslr_late_init(void) >>> +{ >>> + uintptr_t kernel_size; >>> + >>> + /* Clear original kernel image. */ >>> + if (kaslr_offset) { >>> + kernel_size = (uintptr_t) _end - (uintptr_t) _start; >> >> kernel_size = (uintptr_t) _end - (uintptr_t) _start + 1; > > OK, change it in the next version. Thanks. > >> >>> + memset((void *)PAGE_OFFSET, 0, kernel_size); >> >> I have been thinking again about our discussion regarding PAGE_OFFSET: >> PAGE_OFFSET actually points to the address where the kernel was loaded, >> not the beginning of memory, that's a bit weird. >> >> Just saying that here, because it took me a few seconds to remember that >> and understand what you were doing here. > > In non-kaslr case, we load the kernel to PAGE_OFFSET which points to, > so we clear the old kernel image through PAGE_OFFSET here. Certainly, > we could use a symbol to record the start address of the old kernel > image instead of PAGE_OFFSET here. I don't see other architectures > changing PAGE_OFFSET after copying the kernel to the new location in > kaslr. If you think the PAGE_OFFSET needs to be changed, we need to > give another way to make the page table could create the mappings for > the whole memory and memblock/buddy system could see the whole memory > after the kernel moves. > >> >>> + set_memory_nx(PAGE_OFFSET, kaslr_offset >> PAGE_SHIFT); >> >> Again, I certainly missed something but when do you use old kernel >> mappings ? > > We use old kernel mappings when KASLR calculates the random offset, at > that moment, kernel is running on old kernel location.
Yes but haven't you already cleared the page table from the mappings for the old kernel in clear_page_tables called in setup_vm of the new kernel ?
Alex
> >> >>> + } >>> +} >>> + >>> uintptr_t __init kaslr_early_init(void) >>> { >>> u64 seed; >>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c >>> index 34c6ecf2c599..08e2ce170533 100644 >>> --- a/arch/riscv/mm/init.c >>> +++ b/arch/riscv/mm/init.c >>> @@ -15,6 +15,7 @@ >>> #include <linux/set_memory.h> >>> #ifdef CONFIG_RELOCATABLE >>> #include <linux/elf.h> >>> +#include <asm/kaslr.h> >>> #endif >>> >>> #include <asm/fixmap.h> >>> @@ -649,6 +650,11 @@ static void __init setup_vm_final(void) >>> /* Move to swapper page table */ >>> csr_write(CSR_SATP, PFN_DOWN(__pa_symbol(swapper_pg_dir)) | SATP_MODE); >>> local_flush_tlb_all(); >>> + >>> +#ifdef CONFIG_RANDOMIZE_BASE >>> + /* Clear orignial kernel image and set the right permission. */ >>> + kaslr_late_init(); >>> +#endif >>> } >>> >>> void free_initmem(void) >>> >> >> Alex
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