v4.19.13 snapshot.
diff --git a/mm/usercopy.c b/mm/usercopy.c
new file mode 100644
index 0000000..852eb4e
--- /dev/null
+++ b/mm/usercopy.c
@@ -0,0 +1,306 @@
+/*
+ * 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 <linux/sched.h>
+#include <linux/sched/task.h>
+#include <linux/sched/task_stack.h>
+#include <linux/thread_info.h>
+#include <linux/atomic.h>
+#include <linux/jump_label.h>
+#include <asm/sections.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: fully on the stack (when can't do frame-checking)
+ * 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
+ * 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;
+
+ 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 usercopy_warn(const char *name, const char *detail, bool to_user,
+ unsigned long offset, unsigned long len)
+{
+ WARN_ONCE(1, "Bad or missing usercopy whitelist? 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);
+}
+
+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 < 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);
+}
+
+/* Checks for allocs that are marked in some way as spanning multiple pages. */
+static inline void check_page_span(const void *ptr, unsigned long n,
+ struct page *page, bool to_user)
+{
+#ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN
+ const void *end = ptr + n - 1;
+ struct page *endpage;
+ bool is_reserved, is_cma;
+
+ /*
+ * 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)
+ usercopy_abort("rodata", NULL, to_user, 0, n);
+ return;
+ }
+
+ /* Allow kernel data region (if not marked as Reserved). */
+ if (ptr >= (const void *)_sdata && end <= (const void *)_edata)
+ return;
+
+ /* Allow kernel bss region (if not marked as Reserved). */
+ if (ptr >= (const void *)__bss_start &&
+ end <= (const void *)__bss_stop)
+ return;
+
+ /* 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;
+
+ /* Allow if fully inside the same compound (__GFP_COMP) page. */
+ endpage = virt_to_head_page(end);
+ if (likely(endpage == page))
+ return;
+
+ /*
+ * Reject if range is entirely either Reserved (i.e. special or
+ * device memory), or CMA. Otherwise, reject since the object spans
+ * several independently allocated pages.
+ */
+ is_reserved = PageReserved(page);
+ is_cma = is_migrate_cma_page(page);
+ if (!is_reserved && !is_cma)
+ usercopy_abort("spans multiple pages", NULL, to_user, 0, n);
+
+ for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
+ page = virt_to_head_page(ptr);
+ if (is_reserved && !PageReserved(page))
+ usercopy_abort("spans Reserved and non-Reserved pages",
+ NULL, to_user, 0, n);
+ if (is_cma && !is_migrate_cma_page(page))
+ usercopy_abort("spans CMA and non-CMA pages", NULL,
+ to_user, 0, n);
+ }
+#endif
+}
+
+static inline void check_heap_object(const void *ptr, unsigned long n,
+ bool to_user)
+{
+ struct page *page;
+
+ if (!virt_addr_valid(ptr))
+ return;
+
+ page = virt_to_head_page(ptr);
+
+ if (PageSlab(page)) {
+ /* Check slab allocator for flags and size. */
+ __check_heap_object(ptr, n, page, to_user);
+ } else {
+ /* Verify object does not incorrectly span multiple pages. */
+ check_page_span(ptr, n, page, to_user);
+ }
+}
+
+static DEFINE_STATIC_KEY_FALSE_RO(bypass_usercopy_checks);
+
+/*
+ * Validates that the given object is:
+ * - not bogus address
+ * - known-safe heap or stack object
+ * - not in kernel text
+ */
+void __check_object_size(const void *ptr, unsigned long n, bool to_user)
+{
+ if (static_branch_unlikely(&bypass_usercopy_checks))
+ return;
+
+ /* 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 heap object. */
+ check_heap_object(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, 0, n);
+ }
+
+ /* 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 = true;
+
+static int __init parse_hardened_usercopy(char *str)
+{
+ return strtobool(str, &enable_checks);
+}
+
+__setup("hardened_usercopy=", parse_hardened_usercopy);
+
+static int __init set_hardened_usercopy(void)
+{
+ if (enable_checks == false)
+ static_branch_enable(&bypass_usercopy_checks);
+ return 1;
+}
+
+late_initcall(set_hardened_usercopy);