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Message-ID: <148ccc89-a277-a1bb-7779-d1b1dea59e43@ghiti.fr>
Date: Wed, 6 Jan 2021 03:16:56 -0500
From: Alex Ghiti <alex@...ti.fr>
To: Anup Patel <anup@...infault.org>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Zong Li <zong.li@...ive.com>, Christoph Hellwig <hch@....de>,
Ard Biesheuvel <ardb@...nel.org>,
Arnd Bergmann <arnd@...db.de>,
linux-efi <linux-efi@...r.kernel.org>,
linux-arch@...r.kernel.org,
linux-riscv <linux-riscv@...ts.infradead.org>,
"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 01/12] riscv: Move kernel mapping outside of linear
mapping
Le 1/6/21 à 1:44 AM, Anup Patel a écrit :
> On Wed, Jan 6, 2021 at 12:06 PM Alex Ghiti <alex@...ti.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@...ti.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@...db.de>
>>>> Signed-off-by: Alexandre Ghiti <alex@...ti.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.
>
Ok I'll do that.
I realize the naming is confusing, this area does not belong to vmalloc
anymore, I'll change that too.
Thanks again,
>>
>>>>
>>>> /*
>>>> * 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@...infault.org>
>>
>> Thanks for your time Anup,
>>
>>>
>>> Regards,
>>> Anup
>>>
>>
>> Alex
>
> Regards,
> Anup
>
Alex
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