[RFC PATCH 01/12] riscv: Move kernel mapping outside of linear mapping
Anup Patel
anup at brainfault.org
Wed Jan 6 01:44:50 EST 2021
On Wed, Jan 6, 2021 at 12:06 PM Alex Ghiti <alex at ghiti.fr> wrote:
>
> 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.
Makes sense. Please add more detailed comment instead of single-line comment.
>
> >>
> >> /*
> >> * 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
Regards,
Anup
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