Re: [PATCHv2 8/8] x86/mm: Allow to have userspace mappings above 47-bits

From: Dmitry Safonov
Date: Fri Apr 07 2017 - 07:36:26 EST

On 04/07/2017 02:24 AM, 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.

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@xxxxxxxxxxxxxxx>
Cc: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
---
arch/x86/include/asm/elf.h | 2 +-
arch/x86/include/asm/mpx.h | 9 +++++++++
arch/x86/include/asm/processor.h | 10 +++++++---
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, 101 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 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..a98395e89ac6 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 +835,10 @@ 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 (test_thread_flag(TIF_ADDR32) ? \
+ IA32_PAGE_OFFSET : ((1UL << 47) - PAGE_SIZE))

That fixes 32-bit, but we need to adjust some places, AFAICS, I'll
point them below.


/* This decides where the kernel will search for a free chunk of vm
* space during mmap's.
@@ -847,7 +851,7 @@ 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 +874,7 @@ 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)

#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);

That looks not working.
`end' is choosed between tasksize_32bit() and tasksize_64bit().
Which is ~4Gb or 47-bit. So, info.high_limit will never go
above DEFAULT_MAP_WINDOW with this min().

Can we move this logic into find_start_end()?

May it be something like:
if (in_compat_syscall())
*end = tasksize_32bit();
else if (addr > task_size_64bit())
*end = TASK_SIZE_MAX;
else
*end = tasksize_64bit();

In my point of view, it could be even simpler if we add a parameter
to task_size_64bit():

#define TASK_SIZE_47BIT ((1UL << 47) - PAGE_SIZE))

unsigned long task_size_64bit(int full_addr_space)
{
return (full_addr_space) ? TASK_SIZE_MAX : TASK_SIZE_47BIT;
}

+
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, looks like we do need in_compat_syscall() as you did
because x32 mmap() syscall has 8 byte parameter.
Maybe worth a comment.

Anyway, maybe something like that:
if (addr > tasksize_64bit() && !in_compat_syscall())
info.high_limit += TASK_SIZE_MAX - tasksize_64bit();

This way it's more readable and clear because we don't
need to keep in mind that TIF_ADDR32 flag, while reading.


+
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;
+
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;
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;

My suggestion about new parameter is above, but at least
we need to omit depending on TIF_ADDR32 here and return
64-bit size independent of flag value:

#define TASK_SIZE_47BIT ((1UL << 47) - PAGE_SIZE))
unsigned long task_size_64bit(void)
{
return TASK_SIZE_47BIT;
}

Because for 32-bit ELFs it would be always 4Gb in your
case, while 32-bit ELFs can do 64-bit syscalls.

}

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