Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v1 1/1] Add support for mm->mmap_legacy_base in legacy
 layout
To:     Jinli Zheng <zhengdbu@gmail.com>, paul.walmsley@sifive.com
Cc:     palmer@dabbelt.com, aou@eecs.berkeley.edu, anup.patel@wdc.com,
        sunnanyong@huawei.com, jszhang@kernel.org, penberg@kernel.org,
        guoren@linux.alibaba.com, linux-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org
References: <20210927111150.3518-1-zhengdbu@gmail.com>
From:   Alex Ghiti <alex@ghiti.fr>
Message-ID: <ca177872-8ce8-0cb7-4dbf-2debcb1ce76f@ghiti.fr>
Date:   Sun, 10 Oct 2021 17:33:22 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.14.0
MIME-Version: 1.0
In-Reply-To: <20210927111150.3518-1-zhengdbu@gmail.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Language: fr
Content-Transfer-Encoding: 8bit
Precedence: bulk

Hi Jinli,

Le 27/09/2021 ? 13:11, Jinli Zheng a ?crit?:
> 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);
> +}
>