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Subject[PATCH 5/8] x86/mpx: Do not allow MPX if we have mappings above 47-bit
Date
MPX (without MAWA extension) cannot handle addresses above 47-bit, so we
need to make sure that MPX cannot be enabled if we already have VMA above
the boundary and forbid creating such VMAs once MPX is enabled.

The patch implements mpx_unmapped_area_check() which is called from all
variants of get_unmapped_area() to check if the requested address fits
mpx.

On enabling MPX, we check if we already have any vma above 47-bit
boundary and forbit the enabling if we do.

As long as DEFAULT_MAP_WINDOW is equal to TASK_SIZE_MAX, the change is
nop. It will change when we allow userspace to have mappings above
47-bits.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/include/asm/mpx.h | 9 +++++++++
arch/x86/include/asm/processor.h | 3 +++
arch/x86/kernel/sys_x86_64.c | 9 +++++++++
arch/x86/mm/hugetlbpage.c | 6 ++++++
arch/x86/mm/mpx.c | 33 ++++++++++++++++++++++++++++++++-
5 files changed, 59 insertions(+), 1 deletion(-)

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 6a79547e8ee0..52b5a24dd56d 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -803,6 +803,7 @@ 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

@@ -844,6 +845,8 @@ static inline void spin_lock_prefetch(const void *x)
*/
#define TASK_SIZE_MAX ((1UL << 47) - PAGE_SIZE)

+#define DEFAULT_MAP_WINDOW TASK_SIZE_MAX
+
/* This decides where the kernel will search for a free chunk of vm
* space during mmap's.
*/
diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index 89bd0d6460e1..f840e895d871 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;

@@ -171,6 +176,10 @@ 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 868f02cf58ce..3cf89ad00f87 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 *
@@ -135,6 +136,11 @@ 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/mpx.c b/arch/x86/mm/mpx.c
index 1c34b767c84c..8c8da27e8549 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;
}
@@ -1030,3 +1039,25 @@ 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;
+}
--
2.11.0
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