Messages in this thread | | | From | Zong Li <> | Date | Tue, 7 Apr 2020 19:18:12 +0800 | Subject | Re: [PATCH RFC 6/8] riscv/kaslr: clear the original kernel image |
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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.
> > > + } > > +} > > + > > 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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