1 files changed, 47 insertions, 9 deletions

diff --git a/arch/x86/oprofile/backtrace.c b/arch/x86/oprofile/backtrace.c
index a5b64ab4cd6e..32f78eb46744 100644
--- a/arch/x86/oprofile/backtrace.c
+++ b/arch/x86/oprofile/backtrace.c
@@ -11,10 +11,12 @@
 #include <linux/oprofile.h>
 #include <linux/sched.h>
 #include <linux/mm.h>
+#include <linux/compat.h>
+#include <linux/highmem.h>
+
 #include <asm/ptrace.h>
 #include <asm/uaccess.h>
 #include <asm/stacktrace.h>
-#include <linux/compat.h>
 
 static int backtrace_stack(void *data, char *name)
 {
@@ -36,17 +38,53 @@ static struct stacktrace_ops backtrace_ops = {
         .walk_stack     = print_context_stack,
 };
 
+/* from arch/x86/kernel/cpu/perf_event.c: */
+
+/*
+ * best effort, GUP based copy_from_user() that assumes IRQ or NMI context
+ */
+static unsigned long
+copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
+{
+        unsigned long offset, addr = (unsigned long)from;
+        unsigned long size, len = 0;
+        struct page *page;
+        void *map;
+        int ret;
+
+        do {
+                ret = __get_user_pages_fast(addr, 1, 0, &page);
+                if (!ret)
+                        break;
+
+                offset = addr & (PAGE_SIZE - 1);
+                size = min(PAGE_SIZE - offset, n - len);
+
+                map = kmap_atomic(page);
+                memcpy(to, map+offset, size);
+                kunmap_atomic(map);
+                put_page(page);
+
+                len  += size;
+                to   += size;
+                addr += size;
+
+        } while (len < n);
+
+        return len;
+}
+
 #ifdef CONFIG_COMPAT
 static struct stack_frame_ia32 *
 dump_user_backtrace_32(struct stack_frame_ia32 *head)
 {
+        /* Also check accessibility of one struct frame_head beyond: */
         struct stack_frame_ia32 bufhead[2];
         struct stack_frame_ia32 *fp;
+        unsigned long bytes;
 
-        /* Also check accessibility of one struct frame_head beyond */
-        if (!access_ok(VERIFY_READ, head, sizeof(bufhead)))
-                return NULL;
-        if (__copy_from_user_inatomic(bufhead, head, sizeof(bufhead)))
+        bytes = copy_from_user_nmi(bufhead, head, sizeof(bufhead));
+        if (bytes != sizeof(bufhead))
                 return NULL;
 
         fp = (struct stack_frame_ia32 *) compat_ptr(bufhead[0].next_frame);
@@ -87,12 +125,12 @@ x86_backtrace_32(struct pt_regs * const regs, unsigned int depth)
 
 static struct stack_frame *dump_user_backtrace(struct stack_frame *head)
 {
+        /* Also check accessibility of one struct frame_head beyond: */
         struct stack_frame bufhead[2];
+        unsigned long bytes;
 
-        /* Also check accessibility of one struct stack_frame beyond */
-        if (!access_ok(VERIFY_READ, head, sizeof(bufhead)))
-                return NULL;
-        if (__copy_from_user_inatomic(bufhead, head, sizeof(bufhead)))
+        bytes = copy_from_user_nmi(bufhead, head, sizeof(bufhead));
+        if (bytes != sizeof(bufhead))
                 return NULL;
 
         oprofile_add_trace(bufhead[0].return_address);