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SubjectRe: [PATCH 8/8] x86/mm: Allow to have userspace mappings above 47-bits
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Hi Kirill,

On 04/06/2017 05:01 PM, Kirill A. Shutemov wrote:
> On x86, 5-level paging enables 56-bit userspace virtual address space.
> Not all user space is ready to handle wide addresses. It's known that
> at least some JIT compilers use higher bits in pointers to encode their
> information. It collides with valid pointers with 5-level paging and
> leads to crashes.
>
> To mitigate this, we are not going to allocate virtual address space
> above 47-bit by default.
>
> But userspace can ask for allocation from full address space by
> specifying hint address (with or without MAP_FIXED) above 47-bits.
>
> If hint address set above 47-bit, but MAP_FIXED is not specified, we try
> to look for unmapped area by specified address. If it's already
> occupied, we look for unmapped area in *full* address space, rather than
> from 47-bit window.

Do you wish after the first over-47-bit mapping the following mmap()
calls return also over-47-bits if there is free space?
It so, you could simplify all this code by changing only mm->mmap_base
on the first over-47-bit mmap() call.
This will do simple trick.

>
> This approach helps to easily make application's memory allocator aware
> about large address space without manually tracking allocated virtual
> address space.
>
> One important case we need to handle here is interaction with MPX.
> MPX (without MAWA( extension cannot handle addresses above 47-bit, so we
> need to make sure that MPX cannot be enabled we already have VMA above
> the boundary and forbid creating such VMAs once MPX is enabled.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
> ---
> arch/x86/include/asm/elf.h | 2 +-
> arch/x86/include/asm/mpx.h | 9 +++++++++
> arch/x86/include/asm/processor.h | 9 ++++++---
> arch/x86/kernel/sys_x86_64.c | 28 +++++++++++++++++++++++++++-
> arch/x86/mm/hugetlbpage.c | 27 ++++++++++++++++++++++++---
> arch/x86/mm/mmap.c | 2 +-
> arch/x86/mm/mpx.c | 33 ++++++++++++++++++++++++++++++++-
> 7 files changed, 100 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
> index d4d3ed456cb7..67260dbe1688 100644
> --- a/arch/x86/include/asm/elf.h
> +++ b/arch/x86/include/asm/elf.h
> @@ -250,7 +250,7 @@ extern int force_personality32;
> the loader. We need to make sure that it is out of the way of the program
> that it will "exec", and that there is sufficient room for the brk. */
>
> -#define ELF_ET_DYN_BASE (TASK_SIZE / 3 * 2)
> +#define ELF_ET_DYN_BASE (DEFAULT_MAP_WINDOW / 3 * 2)

This will kill 32-bit userspace:
As DEFAULT_MAP_WINDOW is defined as what previously was TASK_SIZE_MAX,
not TASK_SIZE, for ia32/x32 ELF_ET_DYN_BASE will be over 4Gb.

Here is the test:
[root@localhost test]# cat hello-world.c
#include <stdio.h>

int main(int argc, char **argv)
{
printf("Maybe this world is another planet's hell.\n");
return 0;
}
[root@localhost test]# gcc -m32 hello-world.c -o hello-world
[root@localhost test]# ./hello-world
[ 35.306726] hello-world[1948]: segfault at ffa5288c ip
00000000f77b5a82 sp 00000000ffa52890 error 6 in ld-2.23.so[f77b5000+23000]
Segmentation fault (core dumped)

So, dynamic base should differ between 32/64-bits as it was with TASK_SIZE.


>
> /* This yields a mask that user programs can use to figure out what
> instruction set this CPU supports. This could be done in user space,
> diff --git a/arch/x86/include/asm/mpx.h b/arch/x86/include/asm/mpx.h
> index a0d662be4c5b..7d7404756bb4 100644
> --- a/arch/x86/include/asm/mpx.h
> +++ b/arch/x86/include/asm/mpx.h
> @@ -73,6 +73,9 @@ static inline void mpx_mm_init(struct mm_struct *mm)
> }
> void mpx_notify_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
> unsigned long start, unsigned long end);
> +
> +unsigned long mpx_unmapped_area_check(unsigned long addr, unsigned long len,
> + unsigned long flags);
> #else
> static inline siginfo_t *mpx_generate_siginfo(struct pt_regs *regs)
> {
> @@ -94,6 +97,12 @@ static inline void mpx_notify_unmap(struct mm_struct *mm,
> unsigned long start, unsigned long end)
> {
> }
> +
> +static inline unsigned long mpx_unmapped_area_check(unsigned long addr,
> + unsigned long len, unsigned long flags)
> +{
> + return addr;
> +}
> #endif /* CONFIG_X86_INTEL_MPX */
>
> #endif /* _ASM_X86_MPX_H */
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 3cada998a402..9f437aea7f57 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -795,6 +795,7 @@ static inline void spin_lock_prefetch(const void *x)
> #define IA32_PAGE_OFFSET PAGE_OFFSET
> #define TASK_SIZE PAGE_OFFSET
> #define TASK_SIZE_MAX TASK_SIZE
> +#define DEFAULT_MAP_WINDOW TASK_SIZE
> #define STACK_TOP TASK_SIZE
> #define STACK_TOP_MAX STACK_TOP
>
> @@ -834,7 +835,9 @@ static inline void spin_lock_prefetch(const void *x)
> * particular problem by preventing anything from being mapped
> * at the maximum canonical address.
> */
> -#define TASK_SIZE_MAX ((1UL << 47) - PAGE_SIZE)
> +#define TASK_SIZE_MAX ((1UL << __VIRTUAL_MASK_SHIFT) - PAGE_SIZE)
> +
> +#define DEFAULT_MAP_WINDOW ((1UL << 47) - PAGE_SIZE)
>
> /* This decides where the kernel will search for a free chunk of vm
> * space during mmap's.
> @@ -847,7 +850,7 @@ static inline void spin_lock_prefetch(const void *x)
> #define TASK_SIZE_OF(child) ((test_tsk_thread_flag(child, TIF_ADDR32)) ? \
> IA32_PAGE_OFFSET : TASK_SIZE_MAX)
>
> -#define STACK_TOP TASK_SIZE
> +#define STACK_TOP DEFAULT_MAP_WINDOW
> #define STACK_TOP_MAX TASK_SIZE_MAX
>
> #define INIT_THREAD { \
> @@ -870,7 +873,7 @@ extern void start_thread(struct pt_regs *regs, unsigned long new_ip,
> * space during mmap's.
> */
> #define __TASK_UNMAPPED_BASE(task_size) (PAGE_ALIGN(task_size / 3))
> -#define TASK_UNMAPPED_BASE __TASK_UNMAPPED_BASE(TASK_SIZE)
> +#define TASK_UNMAPPED_BASE __TASK_UNMAPPED_BASE(DEFAULT_MAP_WINDOW)

ditto

>
> #define KSTK_EIP(task) (task_pt_regs(task)->ip)
>
> diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
> index 207b8f2582c7..593a31e93812 100644
> --- a/arch/x86/kernel/sys_x86_64.c
> +++ b/arch/x86/kernel/sys_x86_64.c
> @@ -21,6 +21,7 @@
> #include <asm/compat.h>
> #include <asm/ia32.h>
> #include <asm/syscalls.h>
> +#include <asm/mpx.h>
>
> /*
> * Align a virtual address to avoid aliasing in the I$ on AMD F15h.
> @@ -132,6 +133,10 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
> struct vm_unmapped_area_info info;
> unsigned long begin, end;
>
> + addr = mpx_unmapped_area_check(addr, len, flags);
> + if (IS_ERR_VALUE(addr))
> + return addr;
> +
> if (flags & MAP_FIXED)
> return addr;
>
> @@ -151,7 +156,16 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
> info.flags = 0;
> info.length = len;
> info.low_limit = begin;
> - info.high_limit = end;
> +
> + /*
> + * If hint address is above DEFAULT_MAP_WINDOW, look for unmapped area
> + * in the full address space.
> + */
> + if (addr > DEFAULT_MAP_WINDOW)
> + info.high_limit = min(end, TASK_SIZE);
> + else
> + info.high_limit = min(end, DEFAULT_MAP_WINDOW);
> +
> info.align_mask = 0;
> info.align_offset = pgoff << PAGE_SHIFT;
> if (filp) {
> @@ -171,6 +185,10 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
> unsigned long addr = addr0;
> struct vm_unmapped_area_info info;
>
> + addr = mpx_unmapped_area_check(addr, len, flags);
> + if (IS_ERR_VALUE(addr))
> + return addr;
> +
> /* requested length too big for entire address space */
> if (len > TASK_SIZE)
> return -ENOMEM;
> @@ -195,6 +213,14 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
> info.length = len;
> info.low_limit = PAGE_SIZE;
> info.high_limit = get_mmap_base(0);
> +
> + /*
> + * If hint address is above DEFAULT_MAP_WINDOW, look for unmapped area
> + * in the full address space.
> + */
> + if (addr > DEFAULT_MAP_WINDOW && !in_compat_syscall())
> + info.high_limit += TASK_SIZE - DEFAULT_MAP_WINDOW;

Hmm, TASK_SIZE depends now on TIF_ADDR32, which is set during exec().
That means for ia32/x32 ELF which has TASK_SIZE < 4Gb as TIF_ADDR32
is set, which can do 64-bit syscalls - the subtraction will be
a negative..


> +
> info.align_mask = 0;
> info.align_offset = pgoff << PAGE_SHIFT;
> if (filp) {
> diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
> index 302f43fd9c28..9a0b89252c52 100644
> --- a/arch/x86/mm/hugetlbpage.c
> +++ b/arch/x86/mm/hugetlbpage.c
> @@ -18,6 +18,7 @@
> #include <asm/tlbflush.h>
> #include <asm/pgalloc.h>
> #include <asm/elf.h>
> +#include <asm/mpx.h>
>
> #if 0 /* This is just for testing */
> struct page *
> @@ -87,23 +88,38 @@ static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *file,
> info.low_limit = get_mmap_base(1);
> info.high_limit = in_compat_syscall() ?
> tasksize_32bit() : tasksize_64bit();
> +
> + /*
> + * If hint address is above DEFAULT_MAP_WINDOW, look for unmapped area
> + * in the full address space.
> + */
> + if (addr > DEFAULT_MAP_WINDOW)
> + info.high_limit = TASK_SIZE;
> +
> info.align_mask = PAGE_MASK & ~huge_page_mask(h);
> info.align_offset = 0;
> return vm_unmapped_area(&info);
> }
>
> static unsigned long hugetlb_get_unmapped_area_topdown(struct file *file,
> - unsigned long addr0, unsigned long len,
> + unsigned long addr, unsigned long len,
> unsigned long pgoff, unsigned long flags)
> {
> struct hstate *h = hstate_file(file);
> struct vm_unmapped_area_info info;
> - unsigned long addr;
>
> info.flags = VM_UNMAPPED_AREA_TOPDOWN;
> info.length = len;
> info.low_limit = PAGE_SIZE;
> info.high_limit = get_mmap_base(0);
> +
> + /*
> + * If hint address is above DEFAULT_MAP_WINDOW, look for unmapped area
> + * in the full address space.
> + */
> + if (addr > DEFAULT_MAP_WINDOW && !in_compat_syscall())
> + info.high_limit += TASK_SIZE - DEFAULT_MAP_WINDOW;

ditto

> +
> info.align_mask = PAGE_MASK & ~huge_page_mask(h);
> info.align_offset = 0;
> addr = vm_unmapped_area(&info);
> @@ -118,7 +134,7 @@ static unsigned long hugetlb_get_unmapped_area_topdown(struct file *file,
> VM_BUG_ON(addr != -ENOMEM);
> info.flags = 0;
> info.low_limit = TASK_UNMAPPED_BASE;
> - info.high_limit = TASK_SIZE;
> + info.high_limit = DEFAULT_MAP_WINDOW;

ditto about 32-bits

> addr = vm_unmapped_area(&info);
> }
>
> @@ -135,6 +151,11 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>
> if (len & ~huge_page_mask(h))
> return -EINVAL;
> +
> + addr = mpx_unmapped_area_check(addr, len, flags);
> + if (IS_ERR_VALUE(addr))
> + return addr;
> +
> if (len > TASK_SIZE)
> return -ENOMEM;
>
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 19ad095b41df..d63232a31945 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -44,7 +44,7 @@ unsigned long tasksize_32bit(void)
>
> unsigned long tasksize_64bit(void)
> {
> - return TASK_SIZE_MAX;
> + return DEFAULT_MAP_WINDOW;
> }
>
> static unsigned long stack_maxrandom_size(unsigned long task_size)
> diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
> index cd44ae727df7..a26a1b373fd0 100644
> --- a/arch/x86/mm/mpx.c
> +++ b/arch/x86/mm/mpx.c
> @@ -355,10 +355,19 @@ int mpx_enable_management(void)
> */
> bd_base = mpx_get_bounds_dir();
> down_write(&mm->mmap_sem);
> +
> + /* MPX doesn't support addresses above 47-bits yet. */
> + if (find_vma(mm, DEFAULT_MAP_WINDOW)) {
> + pr_warn_once("%s (%d): MPX cannot handle addresses "
> + "above 47-bits. Disabling.",
> + current->comm, current->pid);
> + ret = -ENXIO;
> + goto out;
> + }
> mm->context.bd_addr = bd_base;
> if (mm->context.bd_addr == MPX_INVALID_BOUNDS_DIR)
> ret = -ENXIO;
> -
> +out:
> up_write(&mm->mmap_sem);
> return ret;
> }
> @@ -1038,3 +1047,25 @@ void mpx_notify_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
> if (ret)
> force_sig(SIGSEGV, current);
> }
> +
> +/* MPX cannot handle addresses above 47-bits yet. */
> +unsigned long mpx_unmapped_area_check(unsigned long addr, unsigned long len,
> + unsigned long flags)
> +{
> + if (!kernel_managing_mpx_tables(current->mm))
> + return addr;
> + if (addr + len <= DEFAULT_MAP_WINDOW)
> + return addr;
> + if (flags & MAP_FIXED)
> + return -ENOMEM;
> +
> + /*
> + * Requested len is larger than whole area we're allowed to map in.
> + * Resetting hinting address wouldn't do much good -- fail early.
> + */
> + if (len > DEFAULT_MAP_WINDOW)
> + return -ENOMEM;
> +
> + /* Look for unmap area within DEFAULT_MAP_WINDOW */
> + return 0;
> +}
>


--
Dmitry
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