forked from Minki/linux
mm: Hardened usercopy
This is the start of porting PAX_USERCOPY into the mainline kernel. This
is the first set of features, controlled by CONFIG_HARDENED_USERCOPY. The
work is based on code by PaX Team and Brad Spengler, and an earlier port
from Casey Schaufler. Additional non-slab page tests are from Rik van Riel.
This patch contains the logic for validating several conditions when
performing copy_to_user() and copy_from_user() on the kernel object
being copied to/from:
- address range doesn't wrap around
- address range isn't NULL or zero-allocated (with a non-zero copy size)
- if on the slab allocator:
- object size must be less than or equal to copy size (when check is
implemented in the allocator, which appear in subsequent patches)
- otherwise, object must not span page allocations (excepting Reserved
and CMA ranges)
- if on the stack
- object must not extend before/after the current process stack
- object must be contained by a valid stack frame (when there is
arch/build support for identifying stack frames)
- object must not overlap with kernel text
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Tested-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Kees Cook
parent
0f60a8efe4
commit
f5509cc18d
@ -155,6 +155,18 @@ void kfree(const void *);
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void kzfree(const void *);
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size_t ksize(const void *);
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#ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR
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const char *__check_heap_object(const void *ptr, unsigned long n,
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struct page *page);
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#else
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static inline const char *__check_heap_object(const void *ptr,
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unsigned long n,
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struct page *page)
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{
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return NULL;
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}
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#endif
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/*
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* Some archs want to perform DMA into kmalloc caches and need a guaranteed
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* alignment larger than the alignment of a 64-bit integer.
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@ -155,6 +155,21 @@ static inline int arch_within_stack_frames(const void * const stack,
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}
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#endif
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#ifdef CONFIG_HARDENED_USERCOPY
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extern void __check_object_size(const void *ptr, unsigned long n,
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bool to_user);
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static inline void check_object_size(const void *ptr, unsigned long n,
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bool to_user)
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{
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__check_object_size(ptr, n, to_user);
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}
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#else
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static inline void check_object_size(const void *ptr, unsigned long n,
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bool to_user)
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{ }
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#endif /* CONFIG_HARDENED_USERCOPY */
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#endif /* __KERNEL__ */
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#endif /* _LINUX_THREAD_INFO_H */
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@ -21,6 +21,9 @@ KCOV_INSTRUMENT_memcontrol.o := n
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KCOV_INSTRUMENT_mmzone.o := n
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KCOV_INSTRUMENT_vmstat.o := n
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# Since __builtin_frame_address does work as used, disable the warning.
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CFLAGS_usercopy.o += $(call cc-disable-warning, frame-address)
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mmu-y := nommu.o
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mmu-$(CONFIG_MMU) := gup.o highmem.o memory.o mincore.o \
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mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \
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@ -99,3 +102,4 @@ obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
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obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
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obj-$(CONFIG_FRAME_VECTOR) += frame_vector.o
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obj-$(CONFIG_DEBUG_PAGE_REF) += debug_page_ref.o
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obj-$(CONFIG_HARDENED_USERCOPY) += usercopy.o
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268
mm/usercopy.c
Normal file
268
mm/usercopy.c
Normal file
@ -0,0 +1,268 @@
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/*
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* This implements the various checks for CONFIG_HARDENED_USERCOPY*,
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* which are designed to protect kernel memory from needless exposure
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* and overwrite under many unintended conditions. This code is based
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* on PAX_USERCOPY, which is:
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*
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* Copyright (C) 2001-2016 PaX Team, Bradley Spengler, Open Source
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* Security Inc.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/mm.h>
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#include <linux/slab.h>
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#include <asm/sections.h>
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enum {
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BAD_STACK = -1,
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NOT_STACK = 0,
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GOOD_FRAME,
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GOOD_STACK,
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};
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/*
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* Checks if a given pointer and length is contained by the current
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* stack frame (if possible).
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*
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* Returns:
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* NOT_STACK: not at all on the stack
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* GOOD_FRAME: fully within a valid stack frame
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* GOOD_STACK: fully on the stack (when can't do frame-checking)
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* BAD_STACK: error condition (invalid stack position or bad stack frame)
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*/
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static noinline int check_stack_object(const void *obj, unsigned long len)
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{
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const void * const stack = task_stack_page(current);
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const void * const stackend = stack + THREAD_SIZE;
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int ret;
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/* Object is not on the stack at all. */
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if (obj + len <= stack || stackend <= obj)
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return NOT_STACK;
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/*
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* Reject: object partially overlaps the stack (passing the
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* the check above means at least one end is within the stack,
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* so if this check fails, the other end is outside the stack).
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*/
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if (obj < stack || stackend < obj + len)
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return BAD_STACK;
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/* Check if object is safely within a valid frame. */
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ret = arch_within_stack_frames(stack, stackend, obj, len);
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if (ret)
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return ret;
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return GOOD_STACK;
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}
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static void report_usercopy(const void *ptr, unsigned long len,
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bool to_user, const char *type)
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{
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pr_emerg("kernel memory %s attempt detected %s %p (%s) (%lu bytes)\n",
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to_user ? "exposure" : "overwrite",
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to_user ? "from" : "to", ptr, type ? : "unknown", len);
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/*
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* For greater effect, it would be nice to do do_group_exit(),
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* but BUG() actually hooks all the lock-breaking and per-arch
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* Oops code, so that is used here instead.
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*/
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BUG();
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}
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/* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */
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static bool overlaps(const void *ptr, unsigned long n, unsigned long low,
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unsigned long high)
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{
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unsigned long check_low = (uintptr_t)ptr;
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unsigned long check_high = check_low + n;
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/* Does not overlap if entirely above or entirely below. */
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if (check_low >= high || check_high < low)
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return false;
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return true;
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}
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/* Is this address range in the kernel text area? */
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static inline const char *check_kernel_text_object(const void *ptr,
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unsigned long n)
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{
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unsigned long textlow = (unsigned long)_stext;
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unsigned long texthigh = (unsigned long)_etext;
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unsigned long textlow_linear, texthigh_linear;
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if (overlaps(ptr, n, textlow, texthigh))
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return "<kernel text>";
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/*
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* Some architectures have virtual memory mappings with a secondary
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* mapping of the kernel text, i.e. there is more than one virtual
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* kernel address that points to the kernel image. It is usually
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* when there is a separate linear physical memory mapping, in that
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* __pa() is not just the reverse of __va(). This can be detected
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* and checked:
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*/
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textlow_linear = (unsigned long)__va(__pa(textlow));
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/* No different mapping: we're done. */
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if (textlow_linear == textlow)
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return NULL;
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/* Check the secondary mapping... */
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texthigh_linear = (unsigned long)__va(__pa(texthigh));
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if (overlaps(ptr, n, textlow_linear, texthigh_linear))
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return "<linear kernel text>";
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return NULL;
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}
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static inline const char *check_bogus_address(const void *ptr, unsigned long n)
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{
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/* Reject if object wraps past end of memory. */
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if (ptr + n < ptr)
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return "<wrapped address>";
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/* Reject if NULL or ZERO-allocation. */
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if (ZERO_OR_NULL_PTR(ptr))
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return "<null>";
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return NULL;
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}
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static inline const char *check_heap_object(const void *ptr, unsigned long n,
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bool to_user)
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{
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struct page *page, *endpage;
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const void *end = ptr + n - 1;
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bool is_reserved, is_cma;
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/*
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* Some architectures (arm64) return true for virt_addr_valid() on
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* vmalloced addresses. Work around this by checking for vmalloc
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* first.
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*/
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if (is_vmalloc_addr(ptr))
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return NULL;
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if (!virt_addr_valid(ptr))
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return NULL;
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page = virt_to_head_page(ptr);
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/* Check slab allocator for flags and size. */
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if (PageSlab(page))
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return __check_heap_object(ptr, n, page);
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/*
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* Sometimes the kernel data regions are not marked Reserved (see
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* check below). And sometimes [_sdata,_edata) does not cover
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* rodata and/or bss, so check each range explicitly.
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*/
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/* Allow reads of kernel rodata region (if not marked as Reserved). */
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if (ptr >= (const void *)__start_rodata &&
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end <= (const void *)__end_rodata) {
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if (!to_user)
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return "<rodata>";
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return NULL;
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}
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/* Allow kernel data region (if not marked as Reserved). */
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if (ptr >= (const void *)_sdata && end <= (const void *)_edata)
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return NULL;
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/* Allow kernel bss region (if not marked as Reserved). */
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if (ptr >= (const void *)__bss_start &&
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end <= (const void *)__bss_stop)
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return NULL;
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/* Is the object wholly within one base page? */
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if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) ==
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((unsigned long)end & (unsigned long)PAGE_MASK)))
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return NULL;
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/* Allow if start and end are inside the same compound page. */
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endpage = virt_to_head_page(end);
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if (likely(endpage == page))
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return NULL;
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/*
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* Reject if range is entirely either Reserved (i.e. special or
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* device memory), or CMA. Otherwise, reject since the object spans
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* several independently allocated pages.
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*/
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is_reserved = PageReserved(page);
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is_cma = is_migrate_cma_page(page);
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if (!is_reserved && !is_cma)
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goto reject;
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for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
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page = virt_to_head_page(ptr);
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if (is_reserved && !PageReserved(page))
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goto reject;
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if (is_cma && !is_migrate_cma_page(page))
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goto reject;
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}
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return NULL;
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reject:
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return "<spans multiple pages>";
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}
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/*
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* Validates that the given object is:
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* - not bogus address
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* - known-safe heap or stack object
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* - not in kernel text
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*/
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void __check_object_size(const void *ptr, unsigned long n, bool to_user)
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{
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const char *err;
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/* Skip all tests if size is zero. */
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if (!n)
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return;
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/* Check for invalid addresses. */
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err = check_bogus_address(ptr, n);
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if (err)
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goto report;
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/* Check for bad heap object. */
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err = check_heap_object(ptr, n, to_user);
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if (err)
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goto report;
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/* Check for bad stack object. */
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switch (check_stack_object(ptr, n)) {
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case NOT_STACK:
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/* Object is not touching the current process stack. */
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break;
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case GOOD_FRAME:
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case GOOD_STACK:
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/*
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* Object is either in the correct frame (when it
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* is possible to check) or just generally on the
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* process stack (when frame checking not available).
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*/
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return;
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default:
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err = "<process stack>";
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goto report;
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}
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/* Check for object in kernel to avoid text exposure. */
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err = check_kernel_text_object(ptr, n);
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if (!err)
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return;
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report:
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report_usercopy(ptr, n, to_user, err);
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}
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EXPORT_SYMBOL(__check_object_size);
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@ -118,6 +118,34 @@ config LSM_MMAP_MIN_ADDR
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this low address space will need the permission specific to the
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systems running LSM.
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config HAVE_HARDENED_USERCOPY_ALLOCATOR
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bool
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help
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The heap allocator implements __check_heap_object() for
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validating memory ranges against heap object sizes in
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support of CONFIG_HARDENED_USERCOPY.
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config HAVE_ARCH_HARDENED_USERCOPY
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bool
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help
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The architecture supports CONFIG_HARDENED_USERCOPY by
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calling check_object_size() just before performing the
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userspace copies in the low level implementation of
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copy_to_user() and copy_from_user().
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config HARDENED_USERCOPY
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bool "Harden memory copies between kernel and userspace"
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depends on HAVE_ARCH_HARDENED_USERCOPY
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select BUG
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help
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This option checks for obviously wrong memory regions when
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copying memory to/from the kernel (via copy_to_user() and
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copy_from_user() functions) by rejecting memory ranges that
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are larger than the specified heap object, span multiple
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separately allocates pages, are not on the process stack,
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or are part of the kernel text. This kills entire classes
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of heap overflow exploits and similar kernel memory exposures.
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source security/selinux/Kconfig
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source security/smack/Kconfig
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source security/tomoyo/Kconfig
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