Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR
From: Kirill A. Shutemov
Date: Mon Feb 20 2017 - 08:15:26 EST
On Sat, Feb 18, 2017 at 12:21:33PM +0300, Kirill A. Shutemov wrote:
> On Fri, Feb 17, 2017 at 12:02:13PM -0800, Linus Torvalds wrote:
> > I also get he feeling that the whole thing is unnecessary. I'm
> > wondering if we should just instead say that the whole 47 vs 56-bit
> > virtual address is _purely_ about "get_unmapped_area()", and nothing
> > else.
> >
> > IOW, I'm wondering if we can't just say that
> >
> > - if the processor and kernel support 56-bit user address space, then
> > you can *always* use the whole space
> >
> > - but by default, get_unmapped_area() will only return mappings that
> > fit in the 47 bit address space.
> >
> > So if you use MAP_FIXED and give an address in the high range, it will
> > just always work, and the MM will always consider the task size to be
> > the full address space.
> >
> > But for the common case where a process does no use MAP_FIXED, the
> > kernel will never give a high address by default, and you have to do
> > the process control thing to say "I want those high addresses".
> >
> > Hmm?
> >
> > In other words, I'd like to at least start out trying to keep the
> > differences between the 47-bit and 56-bit models as simple and minimal
> > as possible. Not make such a big deal out of it.
> >
> > We already have "arch_get_unmapped_area()" that controls the whole
> > "what will non-MAP_FIXED mmap allocations return", so I'd hope that
> > the above kind of semantics could be done without *any* actual
> > TASK_SIZE changes _anywhere_ in the VM code.
> >
> > Comments?
>
> Okay, below is my try on implementing this.
>
> I've chosen to respect hint address even without MAP_FIXED, but only if
> it doesn't collide with other mappings. Otherwise, fallback to look for
> unmapped area within 47-bit window.
>
> Interaction with MPX would requires more work. I'm not yet sure what is the
> right way to address it.
I *think* this should do the trick for MPX too.
Dave, could you check if it looks reasonable for you?
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index e7f155c3045e..9c6315d9aa34 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 0b416d4cf73b..b722499f6aba 100644
--- a/arch/x86/include/asm/mpx.h
+++ b/arch/x86/include/asm/mpx.h
@@ -71,6 +71,9 @@ 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)
{
@@ -92,6 +95,12 @@ 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 e6cfe7ba2d65..492548c87cb1 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -789,6 +789,7 @@ static inline void spin_lock_prefetch(const void *x)
*/
#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
@@ -828,7 +829,9 @@ 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.
@@ -841,7 +844,7 @@ 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 { \
@@ -863,7 +866,7 @@ extern void start_thread(struct pt_regs *regs, unsigned long new_ip,
* This decides where the kernel will search for a free chunk of vm
* space during mmap's.
*/
-#define TASK_UNMAPPED_BASE (PAGE_ALIGN(TASK_SIZE / 3))
+#define TASK_UNMAPPED_BASE (PAGE_ALIGN(DEFAULT_MAP_WINDOW / 3))
#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 a55ed63b9f91..df7bfc635941 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -18,6 +18,7 @@
#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.
@@ -128,6 +129,10 @@ 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;
@@ -147,7 +152,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
info.flags = 0;
info.length = len;
info.low_limit = begin;
- info.high_limit = end;
+ info.high_limit = min(end, DEFAULT_MAP_WINDOW);
info.align_mask = 0;
info.align_offset = pgoff << PAGE_SHIFT;
if (filp) {
@@ -167,6 +172,10 @@ 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;
diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
index 2ae8584b44c7..329d653f7238 100644
--- a/arch/x86/mm/hugetlbpage.c
+++ b/arch/x86/mm/hugetlbpage.c
@@ -15,6 +15,7 @@
#include <asm/tlb.h>
#include <asm/tlbflush.h>
#include <asm/pgalloc.h>
+#include <asm/mpx.h>
#if 0 /* This is just for testing */
struct page *
@@ -82,7 +83,7 @@ static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *file,
info.flags = 0;
info.length = len;
info.low_limit = current->mm->mmap_legacy_base;
- info.high_limit = TASK_SIZE;
+ info.high_limit = DEFAULT_MAP_WINDOW;
info.align_mask = PAGE_MASK & ~huge_page_mask(h);
info.align_offset = 0;
return vm_unmapped_area(&info);
@@ -114,7 +115,7 @@ 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);
}
@@ -131,6 +132,11 @@ 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 d2dc0438d654..a29a830ad341 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -52,7 +52,7 @@ static unsigned long stack_maxrandom_size(void)
* Leave an at least ~128 MB hole with possible stack randomization.
*/
#define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
-#define MAX_GAP (TASK_SIZE/6*5)
+#define MAX_GAP (DEFAULT_MAP_WINDOW/6*5)
static int mmap_is_legacy(void)
{
@@ -90,7 +90,7 @@ static unsigned long mmap_base(unsigned long rnd)
else if (gap > MAX_GAP)
gap = MAX_GAP;
- return PAGE_ALIGN(TASK_SIZE - gap - rnd);
+ return PAGE_ALIGN(DEFAULT_MAP_WINDOW - gap - rnd);
}
/*
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index af59f808742f..794b26661711 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -354,10 +354,19 @@ 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;
}
@@ -1037,3 +1046,20 @@ 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;
+ if (len > DEFAULT_MAP_WINDOW)
+ return -ENOMEM;
+
+ /* Look for unmap area within DEFAULT_MAP_WINDOW */
+ return 0;
+}
--
Kirill A. Shutemov