// SPDX-License-Identifier: GPL-2.0-only/* * 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. */#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include <linux/mm.h>#include <linux/highmem.h>#include <linux/kstrtox.h>#include <linux/slab.h>#include <linux/sched.h>#include <linux/sched/task.h>#include <linux/sched/task_stack.h>#include <linux/ucopysize.h>#include <linux/vmalloc.h>#include <linux/atomic.h>#include <linux/jump_label.h>#include <asm/sections.h>#include "slab.h" /* * Checks if a given pointer and length is contained by the current * stack frame (if possible). * * Returns: *	NOT_STACK: not at all on the stack *	GOOD_FRAME: fully within a valid stack frame *	GOOD_STACK: within the current stack (when can't frame-check exactly) *	BAD_STACK: error condition (invalid stack position or bad stack frame) */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 NOT_STACK; 	/*	 * Reject: object partially overlaps the stack (passing 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 BAD_STACK; 	/* Check if object is safely within a valid frame. */	ret = arch_within_stack_frames(stack, stackend, obj, len);	if (ret)		return ret; 	/* Finally, check stack depth if possible. */#ifdef CONFIG_ARCH_HAS_CURRENT_STACK_POINTER	if (IS_ENABLED(CONFIG_STACK_GROWSUP)) {		if ((void *)current_stack_pointer < obj + len)			return BAD_STACK;	} else {		if (obj < (void *)current_stack_pointer)			return BAD_STACK;	}#endif 	return GOOD_STACK;} /* * If these functions are reached, then CONFIG_HARDENED_USERCOPY has found * an unexpected state during a copy_from_user() or copy_to_user() call. * There are several checks being performed on the buffer by the * __check_object_size() function. Normal stack buffer usage should never * trip the checks, and kernel text addressing will always trip the check. * For cache objects, it is checking that only the whitelisted range of * bytes for a given cache is being accessed (via the cache's usersize and * useroffset fields). To adjust a cache whitelist, use the usercopy-aware * kmem_cache_create_usercopy() function to create the cache (and * carefully audit the whitelist range). */void __noreturn usercopy_abort(const char *name, const char *detail,			       bool to_user, unsigned long offset,			       unsigned long len){	pr_emerg("Kernel memory %s attempt detected %s %s%s%s%s (offset %lu, size %lu)!\n",		 to_user ? "exposure" : "overwrite",		 to_user ? "from" : "to",		 name ? : "unknown?!",		 detail ? " '" : "", detail ? : "", detail ? "'" : "",		 offset, len); 	/*	 * For greater effect, it would be nice to do do_group_exit(),	 * but BUG() actually hooks all the lock-breaking and per-arch	 * Oops code, so that is used here instead.	 */	BUG();} /* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */static bool overlaps(const unsigned long ptr, unsigned long n,		     unsigned long low, unsigned long high){	const unsigned long check_low = 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 void check_kernel_text_object(const unsigned long ptr,					    unsigned long n, bool to_user){	unsigned long textlow = (unsigned long)_stext;	unsigned long texthigh = (unsigned long)_etext;	unsigned long textlow_linear, texthigh_linear; 	if (overlaps(ptr, n, textlow, texthigh))		usercopy_abort("kernel text", NULL, to_user, ptr - textlow, n); 	/*	 * Some architectures have virtual memory mappings with a secondary	 * mapping of the kernel text, i.e. there is more than one virtual	 * kernel address that points to the kernel image. It is usually	 * when there is a separate linear physical memory mapping, in that	 * __pa() is not just the reverse of __va(). This can be detected	 * and checked:	 */	textlow_linear = (unsigned long)lm_alias(textlow);	/* No different mapping: we're done. */	if (textlow_linear == textlow)		return; 	/* Check the secondary mapping... */	texthigh_linear = (unsigned long)lm_alias(texthigh);	if (overlaps(ptr, n, textlow_linear, texthigh_linear))		usercopy_abort("linear kernel text", NULL, to_user,			       ptr - textlow_linear, n);} static inline void check_bogus_address(const unsigned long ptr, unsigned long n,				       bool to_user){	/* Reject if object wraps past end of memory. */	if (ptr + (n - 1) < ptr)		usercopy_abort("wrapped address", NULL, to_user, 0, ptr + n); 	/* Reject if NULL or ZERO-allocation. */	if (ZERO_OR_NULL_PTR(ptr))		usercopy_abort("null address", NULL, to_user, ptr, n);} static inline void check_heap_object(const void *ptr, unsigned long n,				     bool to_user){	unsigned long addr = (unsigned long)ptr;	unsigned long offset;	struct page *page;	struct slab *slab; 	if (is_kmap_addr(ptr)) {		offset = offset_in_page(ptr);		if (n > PAGE_SIZE - offset)			usercopy_abort("kmap", NULL, to_user, offset, n);		return;	} 	if (is_vmalloc_addr(ptr) && !pagefault_disabled()) {		struct vmap_area *area = find_vmap_area(addr); 		if (!area)			usercopy_abort("vmalloc", "no area", to_user, 0, n); 		if (n > area->va_end - addr) {			offset = addr - area->va_start;			usercopy_abort("vmalloc", NULL, to_user, offset, n);		}		return;	} 	if (!virt_addr_valid(ptr))		return; 	page = virt_to_page(ptr);	slab = page_slab(page);	if (slab) {		/* Check slab allocator for flags and size. */		__check_heap_object(ptr, n, slab, to_user);	} else if (PageCompound(page)) {		page = compound_head(page);		offset = ptr - page_address(page);		if (n > page_size(page) - offset)			usercopy_abort("page alloc", NULL, to_user, offset, n);	} 	/*	 * We cannot check non-compound pages.  They might be part of	 * a large allocation, in which case crossing a page boundary	 * is fine.	 */} DEFINE_STATIC_KEY_MAYBE_RO(CONFIG_HARDENED_USERCOPY_DEFAULT_ON,			   validate_usercopy_range);EXPORT_SYMBOL(validate_usercopy_range); /* * Validates that the given object is: * - not bogus address * - fully contained by stack (or stack frame, when available) * - fully within SLAB object (or object whitelist area, when available) * - not in kernel text */void __check_object_size(const void *ptr, unsigned long n, bool to_user){	/* Skip all tests if size is zero. */	if (!n)		return; 	/* Check for invalid addresses. */	check_bogus_address((const unsigned long)ptr, n, to_user); 	/* Check for bad stack object. */	switch (check_stack_object(ptr, n)) {	case NOT_STACK:		/* Object is not touching the current process stack. */		break;	case GOOD_FRAME:	case GOOD_STACK:		/*		 * 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:		usercopy_abort("process stack", NULL, to_user,#ifdef CONFIG_ARCH_HAS_CURRENT_STACK_POINTER			IS_ENABLED(CONFIG_STACK_GROWSUP) ?				ptr - (void *)current_stack_pointer :				(void *)current_stack_pointer - ptr,#else			0,#endif			n);	} 	/* Check for bad heap object. */	check_heap_object(ptr, n, to_user); 	/* Check for object in kernel to avoid text exposure. */	check_kernel_text_object((const unsigned long)ptr, n, to_user);}EXPORT_SYMBOL(__check_object_size); static bool enable_checks __initdata =		IS_ENABLED(CONFIG_HARDENED_USERCOPY_DEFAULT_ON); static int __init parse_hardened_usercopy(char *str){	if (kstrtobool(str, &enable_checks))		pr_warn("Invalid option string for hardened_usercopy: '%s'\n",			str);	return 1;} __setup("hardened_usercopy=", parse_hardened_usercopy); static int __init set_hardened_usercopy(void){	if (enable_checks)		static_branch_enable(&validate_usercopy_range);	else		static_branch_disable(&validate_usercopy_range);	return 1;} late_initcall(set_hardened_usercopy);