On Wed, Jul 13, 2016 at 02:55:55PM -0700, Kees Cook wrote: > 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 > - if on the stack > - object must not extend before/after the current process task > - object must be contained by the current 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@xxxxxxxxxxxx> > --- > arch/Kconfig | 7 ++ > include/linux/slab.h | 12 +++ > include/linux/thread_info.h | 15 +++ > mm/Makefile | 4 + > mm/usercopy.c | 219 ++++++++++++++++++++++++++++++++++++++++++++ > security/Kconfig | 27 ++++++ > 6 files changed, 284 insertions(+) > create mode 100644 mm/usercopy.c > > diff --git a/arch/Kconfig b/arch/Kconfig > index 5e2776562035..195ee4cc939a 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -433,6 +433,13 @@ config HAVE_ARCH_WITHIN_STACK_FRAMES > and similar) by implementing an inline arch_within_stack_frames(), > which is used by CONFIG_HARDENED_USERCOPY. > > +config HAVE_ARCH_LINEAR_KERNEL_MAPPING > + bool > + help > + An architecture should select this if it has a secondary linear > + mapping of the kernel text. This is used to verify that kernel > + text exposures are not visible under CONFIG_HARDENED_USERCOPY. > + > config HAVE_CONTEXT_TRACKING > bool > help > diff --git a/include/linux/slab.h b/include/linux/slab.h > index aeb3e6d00a66..96a16a3fb7cb 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -155,6 +155,18 @@ void kfree(const void *); > void kzfree(const void *); > size_t ksize(const void *); > > +#ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR > +const char *__check_heap_object(const void *ptr, unsigned long n, > + struct page *page); > +#else > +static inline const char *__check_heap_object(const void *ptr, > + unsigned long n, > + struct page *page) > +{ > + return NULL; > +} > +#endif > + > /* > * Some archs want to perform DMA into kmalloc caches and need a guaranteed > * alignment larger than the alignment of a 64-bit integer. > diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h > index 3d5c80b4391d..f24b99eac969 100644 > --- a/include/linux/thread_info.h > +++ b/include/linux/thread_info.h > @@ -155,6 +155,21 @@ static inline int arch_within_stack_frames(const void * const stack, > } > #endif > > +#ifdef CONFIG_HARDENED_USERCOPY > +extern void __check_object_size(const void *ptr, unsigned long n, > + bool to_user); > + > +static inline void check_object_size(const void *ptr, unsigned long n, > + bool to_user) > +{ > + __check_object_size(ptr, n, to_user); > +} > +#else > +static inline void check_object_size(const void *ptr, unsigned long n, > + bool to_user) > +{ } > +#endif /* CONFIG_HARDENED_USERCOPY */ > + > #endif /* __KERNEL__ */ > > #endif /* _LINUX_THREAD_INFO_H */ > diff --git a/mm/Makefile b/mm/Makefile > index 78c6f7dedb83..32d37247c7e5 100644 > --- a/mm/Makefile > +++ b/mm/Makefile > @@ -21,6 +21,9 @@ KCOV_INSTRUMENT_memcontrol.o := n > KCOV_INSTRUMENT_mmzone.o := n > KCOV_INSTRUMENT_vmstat.o := n > > +# Since __builtin_frame_address does work as used, disable the warning. > +CFLAGS_usercopy.o += $(call cc-disable-warning, frame-address) > + > mmu-y := nommu.o > mmu-$(CONFIG_MMU) := gup.o highmem.o memory.o mincore.o \ > mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \ > @@ -99,3 +102,4 @@ obj-$(CONFIG_USERFAULTFD) += userfaultfd.o > obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o > obj-$(CONFIG_FRAME_VECTOR) += frame_vector.o > obj-$(CONFIG_DEBUG_PAGE_REF) += debug_page_ref.o > +obj-$(CONFIG_HARDENED_USERCOPY) += usercopy.o > diff --git a/mm/usercopy.c b/mm/usercopy.c > new file mode 100644 > index 000000000000..4161a1fb1909 > --- /dev/null > +++ b/mm/usercopy.c > @@ -0,0 +1,219 @@ > +/* > + * This implements the various checks for CONFIG_HARDENED_USERCOPY*, > + * which are designed to protect kernel memory from needless exposure > + * and overwrite under many unintended conditions. This code is based > + * on PAX_USERCOPY, which is: > + * > + * Copyright (C) 2001-2016 PaX Team, Bradley Spengler, Open Source > + * Security Inc. > + * > + * This program is free software; you can redistribute it and/or modify > + * it under the terms of the GNU General Public License version 2 as > + * published by the Free Software Foundation. > + * > + */ > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt > + > +#include <linux/mm.h> > +#include <linux/slab.h> > +#include <asm/sections.h> > + > +/* > + * Checks if a given pointer and length is contained by the current > + * stack frame (if possible). > + * > + * 0: not at all on the stack > + * 1: fully within a valid stack frame > + * 2: fully on the stack (when can't do frame-checking) > + * -1: error condition (invalid stack position or bad stack frame) Can we use enums? Makes it easier to read/debug > + */ > +static noinline int check_stack_object(const void *obj, unsigned long len) > +{ > + const void * const stack = task_stack_page(current); > + const void * const stackend = stack + THREAD_SIZE; > + int ret; > + > + /* Object is not on the stack at all. */ > + if (obj + len <= stack || stackend <= obj) > + return 0; > + > + /* > + * Reject: object partially overlaps the stack (passing the > + * the check above means at least one end is within the stack, > + * so if this check fails, the other end is outside the stack). > + */ > + if (obj < stack || stackend < obj + len) > + return -1; > + > + /* Check if object is safely within a valid frame. */ > + ret = arch_within_stack_frames(stack, stackend, obj, len); > + if (ret) > + return ret; > + > + return 2; > +} > + > +static void report_usercopy(const void *ptr, unsigned long len, > + bool to_user, const char *type) > +{ > + pr_emerg("kernel memory %s attempt detected %s %p (%s) (%lu bytes)\n", > + to_user ? "exposure" : "overwrite", > + to_user ? "from" : "to", ptr, type ? : "unknown", len); > + dump_stack(); > + do_group_exit(SIGKILL); SIGKILL -- SIGBUS? > +} > + > +/* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */ > +static bool overlaps(const void *ptr, unsigned long n, unsigned long low, > + unsigned long high) > +{ > + unsigned long check_low = (uintptr_t)ptr; > + unsigned long check_high = check_low + n; > + > + /* Does not overlap if entirely above or entirely below. */ > + if (check_low >= high || check_high < low) > + return false; > + > + return true; > +} > + > +/* Is this address range in the kernel text area? */ > +static inline const char *check_kernel_text_object(const void *ptr, > + unsigned long n) > +{ > + unsigned long textlow = (unsigned long)_stext; > + unsigned long texthigh = (unsigned long)_etext; > + > + if (overlaps(ptr, n, textlow, texthigh)) > + return "<kernel text>"; > + > +#ifdef HAVE_ARCH_LINEAR_KERNEL_MAPPING > + /* Check against linear mapping as well. */ > + if (overlaps(ptr, n, (unsigned long)__va(__pa(textlow)), > + (unsigned long)__va(__pa(texthigh)))) > + return "<linear kernel text>"; > +#endif > + > + return NULL; > +} > + > +static inline const char *check_bogus_address(const void *ptr, unsigned long n) > +{ > + /* Reject if object wraps past end of memory. */ > + if (ptr + n < ptr) > + return "<wrapped address>"; > + > + /* Reject if NULL or ZERO-allocation. */ > + if (ZERO_OR_NULL_PTR(ptr)) > + return "<null>"; > + > + return NULL; > +} > + > +static inline const char *check_heap_object(const void *ptr, unsigned long n, > + bool to_user) > +{ > + struct page *page, *endpage; > + const void *end = ptr + n - 1; > + > + if (!virt_addr_valid(ptr)) > + return NULL; > + > + page = virt_to_head_page(ptr); > + > + /* Check slab allocator for flags and size. */ > + if (PageSlab(page)) > + return __check_heap_object(ptr, n, page); > + > + /* > + * Sometimes the kernel data regions are not marked Reserved (see > + * check below). And sometimes [_sdata,_edata) does not cover > + * rodata and/or bss, so check each range explicitly. > + */ > + > + /* Allow reads of kernel rodata region (if not marked as Reserved). */ > + if (ptr >= (const void *)__start_rodata && > + end <= (const void *)__end_rodata) { > + if (!to_user) > + return "<rodata>"; > + return NULL; > + } > + > + /* Allow kernel data region (if not marked as Reserved). */ > + if (ptr >= (const void *)_sdata && end <= (const void *)_edata) > + return NULL; > + > + /* Allow kernel bss region (if not marked as Reserved). */ > + if (ptr >= (const void *)__bss_start && > + end <= (const void *)__bss_stop) > + return NULL; > + > + /* Is the object wholly within one base page? */ > + if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) == > + ((unsigned long)end & (unsigned long)PAGE_MASK))) > + return NULL; > + > + /* Allow if start and end are inside the same compound page. */ > + endpage = virt_to_head_page(end); > + if (likely(endpage == page)) > + return NULL; > + > + /* Allow special areas, device memory, and sometimes kernel data. */ > + if (PageReserved(page) && PageReserved(endpage)) > + return NULL;a If we came here, it's likely that endpage > page, do we need to check that only the first and last pages are reserved? What about the ones in the middle? > + > + /* Uh oh. The "object" spans several independently allocated pages. */ > + return "<spans multiple pages>"; > +} > + > +/* > + * Validates that the given object is one of: > + * - known safe heap object > + * - known safe stack object > + * - not in kernel text > + */ > +void __check_object_size(const void *ptr, unsigned long n, bool to_user) > +{ > + const char *err; > + > + /* Skip all tests if size is zero. */ > + if (!n) > + return; > + > + /* Check for invalid addresses. */ > + err = check_bogus_address(ptr, n); > + if (err) > + goto report; > + > + /* Check for bad heap object. */ > + err = check_heap_object(ptr, n, to_user); > + if (err) > + goto report; > + > + /* Check for bad stack object. */ > + switch (check_stack_object(ptr, n)) { > + case 0: > + /* Object is not touching the current process stack. */ > + break; > + case 1: > + case 2: > + /* > + * Object is either in the correct frame (when it > + * is possible to check) or just generally on the > + * process stack (when frame checking not available). > + */ > + return; > + default: > + err = "<process stack>"; > + goto report; > + } > + > + /* Check for object in kernel to avoid text exposure. */ > + err = check_kernel_text_object(ptr, n); > + if (!err) > + return; > + > +report: > + report_usercopy(ptr, n, to_user, err); > +} Looks good otherwise Balbir Singh -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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