x86/mm: Improve AMD Bulldozer ASLR workaround

[mirror_ubuntu-artful-kernel.git] / arch / x86 / kernel / sys_x86_64.c

diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index 30277e27431acde9a9320e0b1be4470bddb40e3a..10e0272d789a189b7215100a1d66a676d9b4bbfa 100644 (file)
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -34,10 +34,26 @@ static unsigned long get_align_mask(void)
        return va_align.mask;
 }
 
+/*
+ * To avoid aliasing in the I$ on AMD F15h, the bits defined by the
+ * va_align.bits, [12:upper_bit), are set to a random value instead of
+ * zeroing them. This random value is computed once per boot. This form
+ * of ASLR is known as "per-boot ASLR".
+ *
+ * To achieve this, the random value is added to the info.align_offset
+ * value before calling vm_unmapped_area() or ORed directly to the
+ * address.
+ */
+static unsigned long get_align_bits(void)
+{
+       return va_align.bits & get_align_mask();
+}
+
 unsigned long align_vdso_addr(unsigned long addr)
 {
        unsigned long align_mask = get_align_mask();
-       return (addr + align_mask) & ~align_mask;
+       addr = (addr + align_mask) & ~align_mask;
+       return addr | get_align_bits();
 }
 
 static int __init control_va_addr_alignment(char *str)
@@ -135,8 +151,12 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
        info.length = len;
        info.low_limit = begin;
        info.high_limit = end;
-       info.align_mask = filp ? get_align_mask() : 0;
+       info.align_mask = 0;
        info.align_offset = pgoff << PAGE_SHIFT;
+       if (filp) {
+               info.align_mask = get_align_mask();
+               info.align_offset += get_align_bits();
+       }
        return vm_unmapped_area(&info);
 }
 
@@ -174,8 +194,12 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
        info.length = len;
        info.low_limit = PAGE_SIZE;
        info.high_limit = mm->mmap_base;
-       info.align_mask = filp ? get_align_mask() : 0;
+       info.align_mask = 0;
        info.align_offset = pgoff << PAGE_SHIFT;
+       if (filp) {
+               info.align_mask = get_align_mask();
+               info.align_offset += get_align_bits();
+       }
        addr = vm_unmapped_area(&info);
        if (!(addr & ~PAGE_MASK))
                return addr;