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SubjectRe: [PATCH v1 1/1] Add support for mm->mmap_legacy_base in legacy layout
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Hi Jinli,

Le 27/09/2021 à 13:11, Jinli Zheng a écrit :
> Add support for mm->mmap_legacy_base in the legacy layout
> of the process memory space for the riscv architecture
>

Can you elaborate a bit more? What value does it bring? I remember I had
spent some time to factorize this code with arm64 to offer
ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT config and I had another patchset
to get rid of mmap_legacy_base entirely at
https://lkml.org/lkml/2019/6/19/18 (which never got merged though).

Thanks,

Alex

> Signed-off-by: Jinli Zheng <zhengdbu@gmail.com>
> ---
> arch/riscv/Kconfig | 2 +-
> arch/riscv/include/asm/pgtable.h | 3 +
> arch/riscv/include/asm/processor.h | 1 +
> arch/riscv/mm/Makefile | 2 +-
> arch/riscv/mm/mmap.c | 165 +++++++++++++++++++++++++++++
> 5 files changed, 171 insertions(+), 2 deletions(-)
> create mode 100644 arch/riscv/mm/mmap.c
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 301a54233c7e..e64231592227 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -37,7 +37,7 @@ config RISCV
> select ARCH_SUPPORTS_DEBUG_PAGEALLOC if MMU
> select ARCH_SUPPORTS_HUGETLBFS if MMU
> select ARCH_USE_MEMTEST
> - select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
> + select ARCH_HAS_ELF_RANDOMIZE
> select ARCH_WANT_FRAME_POINTERS
> select ARCH_WANT_HUGE_PMD_SHARE if 64BIT
> select BINFMT_FLAT_NO_DATA_START_OFFSET if !MMU
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 39b550310ec6..107d61371272 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -700,6 +700,9 @@ void misc_mem_init(void);
> extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
> #define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page))
>
> +#define HAVE_ARCH_UNMAPPED_AREA
> +#define HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
> +
> #endif /* !__ASSEMBLY__ */
>
> #endif /* _ASM_RISCV_PGTABLE_H */
> diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> index 46b492c78cbb..e7dc7c1f820a 100644
> --- a/arch/riscv/include/asm/processor.h
> +++ b/arch/riscv/include/asm/processor.h
> @@ -56,6 +56,7 @@ static inline void arch_thread_struct_whitelist(unsigned long *offset,
> #define KSTK_EIP(tsk) (task_pt_regs(tsk)->epc)
> #define KSTK_ESP(tsk) (task_pt_regs(tsk)->sp)
>
> +#define HAVE_ARCH_PICK_MMAP_LAYOUT 1
>
> /* Do necessary setup to start up a newly executed thread. */
> extern void start_thread(struct pt_regs *regs,
> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
> index 7ebaef10ea1b..123c67a2c24a 100644
> --- a/arch/riscv/mm/Makefile
> +++ b/arch/riscv/mm/Makefile
> @@ -10,7 +10,7 @@ KCOV_INSTRUMENT_init.o := n
>
> obj-y += init.o
> obj-y += extable.o
> -obj-$(CONFIG_MMU) += fault.o pageattr.o
> +obj-$(CONFIG_MMU) += fault.o pageattr.o mmap.o
> obj-y += cacheflush.o
> obj-y += context.o
>
> diff --git a/arch/riscv/mm/mmap.c b/arch/riscv/mm/mmap.c
> new file mode 100644
> index 000000000000..6c5818db5a65
> --- /dev/null
> +++ b/arch/riscv/mm/mmap.c
> @@ -0,0 +1,165 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Legacy and flexible mmap layout support
> + *
> + * Copyright (C) 2021 Jinli Zheng <zhengdbu@gmail.com>
> + */
> +
> +#include <linux/personality.h>
> +#include <linux/mm.h>
> +#include <linux/mman.h>
> +#include <linux/random.h>
> +#include <linux/limits.h>
> +#include <linux/security.h>
> +#include <linux/compat.h>
> +#include <linux/sched/mm.h>
> +#include <linux/sched.h>
> +#include <linux/elf-randomize.h>
> +#include <asm/pgtable.h>
> +#include <asm/processor.h>
> +
> +#define SIZE_128M (128*1024*1024UL)
> +
> +/*gap between MMAP and STACK*/
> +#define GAP_MIN SIZE_128M
> +#define GAP_MAX (((TASK_SIZE)/6)*5)
> +
> +static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
> +{
> + unsigned long gap = rlim_stack->rlim_cur;
> +
> + if (gap < GAP_MIN)
> + gap = GAP_MIN;
> + else if (gap > GAP_MAX)
> + gap = GAP_MAX;
> +
> + return PAGE_ALIGN(TASK_SIZE - gap - rnd);
> +}
> +
> +unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
> + unsigned long len, unsigned long pgoff, unsigned long flags)
> +{
> + struct mm_struct *mm = current->mm;
> + struct vm_area_struct *vma, *prev;
> + struct vm_unmapped_area_info info;
> +
> + if (len > TASK_SIZE)
> + return -ENOMEM;
> +
> + if (flags & MAP_FIXED)
> + return addr;
> +
> + if (addr) {
> + addr = PAGE_ALIGN(addr);
> + vma = find_vma_prev(mm, addr, &prev);
> + if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
> + (!vma || addr + len <= vm_start_gap(vma)) &&
> + (!prev || addr >= vm_end_gap(prev)))
> + return addr;
> + }
> +
> + info.flags = 0;
> + info.length = len;
> + info.low_limit = mm->mmap_legacy_base;
> + info.high_limit = TASK_SIZE;
> + info.align_mask = 0;
> + info.align_offset = 0;
> + return vm_unmapped_area(&info);
> +}
> +
> +unsigned long arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
> + unsigned long len, unsigned long pgoff, unsigned long flags)
> +{
> + struct mm_struct *mm = current->mm;
> + struct vm_area_struct *vma, *prev;
> + struct vm_unmapped_area_info info;
> +
> + if (len > TASK_SIZE)
> + return -ENOMEM;
> +
> + if (flags & MAP_FIXED)
> + return addr;
> +
> + if (addr) {
> + addr = PAGE_ALIGN(addr);
> + vma = find_vma_prev(mm, addr, &prev);
> + if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
> + (!vma || addr + len <= vm_start_gap(vma)) &&
> + (!prev || addr >= vm_end_gap(prev)))
> + return addr;
> + }
> +
> + info.flags = VM_UNMAPPED_AREA_TOPDOWN;
> + info.length = len;
> + info.low_limit = max(PAGE_SIZE, mmap_min_addr);
> + info.high_limit = mm->mmap_base;
> + info.align_mask = 0;
> + info.align_offset = 0;
> + addr = vm_unmapped_area(&info);
> +
> + if (offset_in_page(addr)) {
> + VM_BUG_ON(addr != -ENOMEM);
> + info.flags = 0;
> + info.low_limit = TASK_UNMAPPED_BASE;
> + info.high_limit = TASK_SIZE;
> + addr = vm_unmapped_area(&info);
> + }
> +
> + return addr;
> +}
> +
> +unsigned long arch_mmap_rnd(void)
> +{
> + unsigned long rnd;
> +
> +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
> + if (is_compat_task())
> + rnd = get_random_int() & ((1UL << mmap_rnd_compat_bits) - 1);
> + else
> +#endif /*CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS*/
> + rnd = get_random_int() & ((1UL << mmap_rnd_bits) - 1);
> +
> + return rnd << PAGE_SHIFT;
> +}
> +
> +static int mmap_is_legacy(struct rlimit *rlim_stack)
> +{
> + if (current->personality & ADDR_COMPAT_LAYOUT)
> + return 1;
> +
> + if (rlim_stack->rlim_cur == RLIM_INFINITY)
> + return 1;
> +
> + return sysctl_legacy_va_layout;
> +}
> +
> +static void arch_pick_mmap_base(struct mm_struct *mm, struct rlimit *rlim_stack)
> +{
> + unsigned long random;
> +
> + random = (current->flags & PF_RANDOMIZE) ?
> + arch_mmap_rnd() : 0UL;
> +
> + if (mmap_is_legacy(rlim_stack))
> + mm->mmap_legacy_base = TASK_UNMAPPED_BASE + random;
> + else
> + mm->mmap_base = mmap_base(random, rlim_stack);
> +}
> +
> +void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
> +{
> + if (mmap_is_legacy(rlim_stack))
> + mm->get_unmapped_area = arch_get_unmapped_area;
> + else
> + mm->get_unmapped_area = arch_get_unmapped_area_topdown;
> +
> + arch_pick_mmap_base(mm, rlim_stack);
> +}
> +
> +unsigned long arch_randomize_brk(struct mm_struct *mm)
> +{
> + if (!IS_ENABLED(CONFIG_64BIT) || is_compat_task())
> + return randomize_page(mm->brk, SZ_32M);
> +
> + return randomize_page(mm->brk, SZ_1G);
> +}
>

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