Re: [RFC PATCH v2 1/2] Randomization of address chosen by mmap.
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2018-03-22 20:53:14
Also in:
linux-alpha, linux-mm, linux-s390, linux-sh, linuxppc-dev, lkml, sparclinux
On Thu, 22 Mar 2018 19:36:37 +0300 Ilya Smith [off-list ref] wrote:
include/linux/mm.h | 16 ++++-- mm/mmap.c | 164 +++++++++++++++++++++++++++++++++++++++++++++++++++++
You'll be wanting to update the documentation. Documentation/sysctl/kernel.txt and Documentation/admin-guide/kernel-parameters.txt.
quoted hunk ↗ jump to hunk
...@@ -2268,6 +2276,9 @@ extern unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info); static inline unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info) { + /* How about 32 bit process?? */ + if ((current->flags & PF_RANDOMIZE) && randomize_va_space > 3) + return unmapped_area_random(info);
The handling of randomize_va_space is peculiar. Rather than being a bitfield which independently selects different modes, it is treated as a scalar: the larger the value, the more stuff we randomize. I can see the sense in that (and I wonder what randomize_va_space=5 will do). But it is... odd. Why did you select randomize_va_space=4 for this? Is there a mode 3 already and we forgot to document it? Or did you leave a gap for something? If the former, please feel free to fix the documentation (in a separate, preceding patch) while you're in there ;)
quoted hunk ↗ jump to hunk
if (info->flags & VM_UNMAPPED_AREA_TOPDOWN) return unmapped_area_topdown(info); else@@ -2529,11 +2540,6 @@ int drop_caches_sysctl_handler(struct ctl_table *, int, void drop_slab(void); void drop_slab_node(int nid);...@@ -1780,6 +1781,169 @@ unsigned long mmap_region(struct file *file, unsigned long addr, return error; } +unsigned long unmapped_area_random(struct vm_unmapped_area_info *info) +{
This function is just dead code if CONFIG_MMU=n, yes? Let's add the ifdefs to make it go away in that case.
+ struct mm_struct *mm = current->mm; + struct vm_area_struct *vma = NULL; + struct vm_area_struct *visited_vma = NULL; + unsigned long entropy[2]; + unsigned long length, low_limit, high_limit, gap_start, gap_end; + unsigned long addr = 0; + + /* get entropy with prng */ + prandom_bytes(&entropy, sizeof(entropy)); + /* small hack to prevent EPERM result */ + info->low_limit = max(info->low_limit, mmap_min_addr); + ... +found: + /* We found a suitable gap. Clip it with the original high_limit. */ + if (gap_end > info->high_limit) + gap_end = info->high_limit; + gap_end -= info->length; + gap_end -= (gap_end - info->align_offset) & info->align_mask; + /* only one suitable page */ + if (gap_end == gap_start) + return gap_start; + addr = entropy[1] % (min((gap_end - gap_start) >> PAGE_SHIFT, + 0x10000UL));
What does the magic 10000 mean? Isn't a comment needed explaining this?
+ addr = gap_end - (addr << PAGE_SHIFT); + addr += (info->align_offset - addr) & info->align_mask; + return addr; +} ...