[RFC PATCH 01/12] riscv: Move kernel mapping outside of linear mapping
Alex Ghiti
alex at ghiti.fr
Wed Jan 6 01:36:32 EST 2021
Hi Anup,
Le 1/5/21 à 6:40 AM, Anup Patel a écrit :
> On Tue, Jan 5, 2021 at 1:29 AM Alexandre Ghiti <alex at ghiti.fr> wrote:
>>
>> This is a preparatory patch for relocatable kernel and sv48 support.
>>
>> The kernel used to be linked at PAGE_OFFSET address therefore we could use
>> the linear mapping for the kernel mapping. But the relocated kernel base
>> address will be different from PAGE_OFFSET and since in the linear mapping,
>> two different virtual addresses cannot point to the same physical address,
>> the kernel mapping needs to lie outside the linear mapping so that we don't
>> have to copy it at the same physical offset.
>>
>> The kernel mapping is moved to the last 2GB of the address space and then
>> BPF and modules are also pushed to the same range since they have to lie
>> close to the kernel inside a 2GB window.
>>
>> Note then that KASLR implementation will simply have to move the kernel in
>> this 2GB range and modify BPF/modules regions accordingly.
>>
>> In addition, by moving the kernel to the end of the address space, both
>> sv39 and sv48 kernels will be exactly the same without needing to be
>> relocated at runtime.
>
> Awesome ! This is a good approach with no performance impact.
>
>>
>> Suggested-by: Arnd Bergmann <arnd at arndb.de>
>> Signed-off-by: Alexandre Ghiti <alex at ghiti.fr>
>> ---
>> arch/riscv/boot/loader.lds.S | 3 +-
>> arch/riscv/include/asm/page.h | 10 ++++-
>> arch/riscv/include/asm/pgtable.h | 39 +++++++++++++------
>> arch/riscv/kernel/head.S | 3 +-
>> arch/riscv/kernel/module.c | 4 +-
>> arch/riscv/kernel/vmlinux.lds.S | 3 +-
>> arch/riscv/mm/init.c | 65 ++++++++++++++++++++++++--------
>> arch/riscv/mm/physaddr.c | 2 +-
>> 8 files changed, 94 insertions(+), 35 deletions(-)
>>
>> diff --git a/arch/riscv/boot/loader.lds.S b/arch/riscv/boot/loader.lds.S
>> index 47a5003c2e28..62d94696a19c 100644
>> --- a/arch/riscv/boot/loader.lds.S
>> +++ b/arch/riscv/boot/loader.lds.S
>> @@ -1,13 +1,14 @@
>> /* SPDX-License-Identifier: GPL-2.0 */
>>
>> #include <asm/page.h>
>> +#include <asm/pgtable.h>
>>
>> OUTPUT_ARCH(riscv)
>> ENTRY(_start)
>>
>> SECTIONS
>> {
>> - . = PAGE_OFFSET;
>> + . = KERNEL_LINK_ADDR;
>>
>> .payload : {
>> *(.payload)
>> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
>> index 2d50f76efe48..98188e315e8d 100644
>> --- a/arch/riscv/include/asm/page.h
>> +++ b/arch/riscv/include/asm/page.h
>> @@ -90,18 +90,26 @@ typedef struct page *pgtable_t;
>>
>> #ifdef CONFIG_MMU
>> extern unsigned long va_pa_offset;
>> +extern unsigned long va_kernel_pa_offset;
>> extern unsigned long pfn_base;
>> #define ARCH_PFN_OFFSET (pfn_base)
>> #else
>> #define va_pa_offset 0
>> +#define va_kernel_pa_offset 0
>> #define ARCH_PFN_OFFSET (PAGE_OFFSET >> PAGE_SHIFT)
>> #endif /* CONFIG_MMU */
>>
>> extern unsigned long max_low_pfn;
>> extern unsigned long min_low_pfn;
>> +extern unsigned long kernel_virt_addr;
>>
>> #define __pa_to_va_nodebug(x) ((void *)((unsigned long) (x) + va_pa_offset))
>> -#define __va_to_pa_nodebug(x) ((unsigned long)(x) - va_pa_offset)
>> +#define linear_mapping_va_to_pa(x) ((unsigned long)(x) - va_pa_offset)
>> +#define kernel_mapping_va_to_pa(x) \
>> + ((unsigned long)(x) - va_kernel_pa_offset)
>> +#define __va_to_pa_nodebug(x) \
>> + (((x) < KERNEL_LINK_ADDR) ? \
>> + linear_mapping_va_to_pa(x) : kernel_mapping_va_to_pa(x))
>>
>> #ifdef CONFIG_DEBUG_VIRTUAL
>> extern phys_addr_t __virt_to_phys(unsigned long x);
>> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
>> index 183f1f4b2ae6..102b728ca146 100644
>> --- a/arch/riscv/include/asm/pgtable.h
>> +++ b/arch/riscv/include/asm/pgtable.h
>> @@ -11,23 +11,32 @@
>>
>> #include <asm/pgtable-bits.h>
>>
>> -#ifndef __ASSEMBLY__
>> -
>> -/* Page Upper Directory not used in RISC-V */
>> -#include <asm-generic/pgtable-nopud.h>
>> -#include <asm/page.h>
>> -#include <asm/tlbflush.h>
>> -#include <linux/mm_types.h>
>> +#ifndef CONFIG_MMU
>> +#define KERNEL_VIRT_ADDR PAGE_OFFSET
>> +#define KERNEL_LINK_ADDR PAGE_OFFSET
>> +#else
>>
>> -#ifdef CONFIG_MMU
>> +#define ADDRESS_SPACE_END (UL(-1))
>> +/*
>> + * Leave 2GB for kernel, modules and BPF at the end of the address space
>> + */
>> +#define KERNEL_VIRT_ADDR (ADDRESS_SPACE_END - SZ_2G + 1)
>> +#define KERNEL_LINK_ADDR KERNEL_VIRT_ADDR
>>
>> #define VMALLOC_SIZE (KERN_VIRT_SIZE >> 1)
>> #define VMALLOC_END (PAGE_OFFSET - 1)
>> #define VMALLOC_START (PAGE_OFFSET - VMALLOC_SIZE)
>>
>> +/* KASLR should leave at least 128MB for BPF after the kernel */
>> #define BPF_JIT_REGION_SIZE (SZ_128M)
>> -#define BPF_JIT_REGION_START (PAGE_OFFSET - BPF_JIT_REGION_SIZE)
>> -#define BPF_JIT_REGION_END (VMALLOC_END)
>> +#define BPF_JIT_REGION_START PFN_ALIGN((unsigned long)&_end)
>> +#define BPF_JIT_REGION_END (BPF_JIT_REGION_START + BPF_JIT_REGION_SIZE)
>> +
>> +/* Modules always live before the kernel */
>> +#ifdef CONFIG_64BIT
>> +#define VMALLOC_MODULE_START (PFN_ALIGN((unsigned long)&_end) - SZ_2G)
>> +#define VMALLOC_MODULE_END (PFN_ALIGN((unsigned long)&_start))
>> +#endif
>
> This does not look right or I am missing something.
>
> I think the VMALLOC_MODULE_START should be:
> #define VMALLOC_MODULE_START (PFN_ALIGN((unsigned long)&_start) - SZ_2G)
>
I think the patch is correct: worst-case, we want the first address of
the module area to be able to access the last address of the kernel, so
we must use _end and not _start to guarantee that the difference between
those 2 addresses is not greater than 2GB.
>>
>> /*
>> * Roughly size the vmemmap space to be large enough to fit enough
>> @@ -57,9 +66,16 @@
>> #define FIXADDR_SIZE PGDIR_SIZE
>> #endif
>> #define FIXADDR_START (FIXADDR_TOP - FIXADDR_SIZE)
>> -
>> #endif
>>
>> +#ifndef __ASSEMBLY__
>> +
>> +/* Page Upper Directory not used in RISC-V */
>> +#include <asm-generic/pgtable-nopud.h>
>> +#include <asm/page.h>
>> +#include <asm/tlbflush.h>
>> +#include <linux/mm_types.h>
>> +
>> #ifdef CONFIG_64BIT
>> #include <asm/pgtable-64.h>
>> #else
>> @@ -467,6 +483,7 @@ static inline void __kernel_map_pages(struct page *page, int numpages, int enabl
>>
>> #define kern_addr_valid(addr) (1) /* FIXME */
>>
>> +extern char _start[];
>> extern void *dtb_early_va;
>> extern uintptr_t dtb_early_pa;
>> void setup_bootmem(void);
>> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
>> index 7e849797c9c3..66f40c49bf68 100644
>> --- a/arch/riscv/kernel/head.S
>> +++ b/arch/riscv/kernel/head.S
>> @@ -69,7 +69,8 @@ pe_head_start:
>> #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/module.c b/arch/riscv/kernel/module.c
>> index 104fba889cf7..75a0b9541266 100644
>> --- a/arch/riscv/kernel/module.c
>> +++ b/arch/riscv/kernel/module.c
>> @@ -408,12 +408,10 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
>> }
>>
>> #if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
>> -#define VMALLOC_MODULE_START \
>> - max(PFN_ALIGN((unsigned long)&_end - SZ_2G), VMALLOC_START)
>> void *module_alloc(unsigned long size)
>> {
>> return __vmalloc_node_range(size, 1, VMALLOC_MODULE_START,
>> - VMALLOC_END, GFP_KERNEL,
>> + VMALLOC_MODULE_END, GFP_KERNEL,
>> PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
>> __builtin_return_address(0));
>> }
>> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
>> index 3ffbd6cbdb86..c21dc46f41be 100644
>> --- a/arch/riscv/kernel/vmlinux.lds.S
>> +++ b/arch/riscv/kernel/vmlinux.lds.S
>> @@ -4,7 +4,8 @@
>> * Copyright (C) 2017 SiFive
>> */
>>
>> -#define LOAD_OFFSET PAGE_OFFSET
>> +#include <asm/pgtable.h>
>> +#define LOAD_OFFSET KERNEL_LINK_ADDR
>> #include <asm/vmlinux.lds.h>
>> #include <asm/page.h>
>> #include <asm/cache.h>
>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>> index 8e577f14f120..9d06ff0e015a 100644
>> --- a/arch/riscv/mm/init.c
>> +++ b/arch/riscv/mm/init.c
>> @@ -23,6 +23,9 @@
>>
>> #include "../kernel/head.h"
>>
>> +unsigned long kernel_virt_addr = KERNEL_VIRT_ADDR;
>> +EXPORT_SYMBOL(kernel_virt_addr);
>> +
>> unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
>> __page_aligned_bss;
>> EXPORT_SYMBOL(empty_zero_page);
>> @@ -201,8 +204,12 @@ void __init setup_bootmem(void)
>> #ifdef CONFIG_MMU
>> static struct pt_alloc_ops pt_ops;
>>
>> +/* Offset between linear mapping virtual address and kernel load address */
>> unsigned long va_pa_offset;
>> EXPORT_SYMBOL(va_pa_offset);
>> +/* Offset between kernel mapping virtual address and kernel load address */
>> +unsigned long va_kernel_pa_offset;
>> +EXPORT_SYMBOL(va_kernel_pa_offset);
>> unsigned long pfn_base;
>> EXPORT_SYMBOL(pfn_base);
>>
>> @@ -316,7 +323,7 @@ static phys_addr_t __init alloc_pmd_early(uintptr_t va)
>> {
>> uintptr_t pmd_num;
>>
>> - pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
>> + pmd_num = (va - kernel_virt_addr) >> PGDIR_SHIFT;
>> BUG_ON(pmd_num >= NUM_EARLY_PMDS);
>> return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD];
>> }
>> @@ -431,17 +438,34 @@ 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
>>
>> +static uintptr_t load_pa, load_sz;
>> +
>> +static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
>> +{
>> + uintptr_t va, end_va;
>> +
>> + end_va = kernel_virt_addr + load_sz;
>> + for (va = kernel_virt_addr; va < end_va; va += map_size)
>> + create_pgd_mapping(pgdir, va,
>> + load_pa + (va - kernel_virt_addr),
>> + map_size, PAGE_KERNEL_EXEC);
>> +}
>> +
>> asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>> {
>> - uintptr_t va, pa, end_va;
>> - uintptr_t load_pa = (uintptr_t)(&_start);
>> - uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
>> - uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
>> + uintptr_t pa;
>> + uintptr_t map_size;
>> #ifndef __PAGETABLE_PMD_FOLDED
>> pmd_t fix_bmap_spmd, fix_bmap_epmd;
>> #endif
>>
>> + load_pa = (uintptr_t)(&_start);
>> + load_sz = (uintptr_t)(&_end) - load_pa;
>> + map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
>> +
>> va_pa_offset = PAGE_OFFSET - load_pa;
>> + va_kernel_pa_offset = kernel_virt_addr - load_pa;
>> +
>> pfn_base = PFN_DOWN(load_pa);
>>
>> /*
>> @@ -470,26 +494,22 @@ 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
>>
>> /*
>> - * Setup early PGD covering entire kernel which will allows
>> + * Setup early PGD covering entire kernel which will allow
>> * 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)
>> - create_pgd_mapping(early_pg_dir, va,
>> - load_pa + (va - PAGE_OFFSET),
>> - map_size, PAGE_KERNEL_EXEC);
>> + create_kernel_page_table(early_pg_dir, map_size);
>>
>> #ifndef __PAGETABLE_PMD_FOLDED
>> /* Setup early PMD for DTB */
>> @@ -549,6 +569,7 @@ static void __init setup_vm_final(void)
>> uintptr_t va, map_size;
>> phys_addr_t pa, start, end;
>> u64 i;
>> + static struct vm_struct vm_kernel = { 0 };
>>
>> /**
>> * MMU is enabled at this point. But page table setup is not complete yet.
>> @@ -565,7 +586,7 @@ static void __init setup_vm_final(void)
>> __pa_symbol(fixmap_pgd_next),
>> PGDIR_SIZE, PAGE_TABLE);
>>
>> - /* Map all memory banks */
>> + /* Map all memory banks in the linear mapping */
>> for_each_mem_range(i, &start, &end) {
>> if (start >= end)
>> break;
>> @@ -577,10 +598,22 @@ static void __init setup_vm_final(void)
>> for (pa = start; pa < end; pa += map_size) {
>> va = (uintptr_t)__va(pa);
>> create_pgd_mapping(swapper_pg_dir, va, pa,
>> - map_size, PAGE_KERNEL_EXEC);
>> + map_size, PAGE_KERNEL);
>> }
>> }
>>
>> + /* Map the kernel */
>> + create_kernel_page_table(swapper_pg_dir, PMD_SIZE);
>> +
>> + /* Reserve the vmalloc area occupied by the kernel */
>> + vm_kernel.addr = (void *)kernel_virt_addr;
>> + vm_kernel.phys_addr = load_pa;
>> + vm_kernel.size = (load_sz + PMD_SIZE - 1) & ~(PMD_SIZE - 1);
>> + vm_kernel.flags = VM_MAP | VM_NO_GUARD;
>> + vm_kernel.caller = __builtin_return_address(0);
>> +
>> + vm_area_add_early(&vm_kernel);
>> +
>> /* Clear fixmap PTE and PMD mappings */
>> clear_fixmap(FIX_PTE);
>> clear_fixmap(FIX_PMD);
>> diff --git a/arch/riscv/mm/physaddr.c b/arch/riscv/mm/physaddr.c
>> index e8e4dcd39fed..35703d5ef5fd 100644
>> --- a/arch/riscv/mm/physaddr.c
>> +++ b/arch/riscv/mm/physaddr.c
>> @@ -23,7 +23,7 @@ EXPORT_SYMBOL(__virt_to_phys);
>>
>> phys_addr_t __phys_addr_symbol(unsigned long x)
>> {
>> - unsigned long kernel_start = (unsigned long)PAGE_OFFSET;
>> + unsigned long kernel_start = (unsigned long)kernel_virt_addr;
>> unsigned long kernel_end = (unsigned long)_end;
>>
>> /*
>> --
>> 2.20.1
>>
>
> Apart from the minor comment above, this looks good to me.
>
> Reviewed-by: Anup Patel <anup at brainfault.org>
Thanks for your time Anup,
>
> Regards,
> Anup
>
Alex
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