[PATCH 09/17] prmem: hardened usercopy

[Igor Stoppa]

Prevent leaks of protected memory to userspace.
The protection from overwrited from userspace is already available, once
the memory is write protected.

Signed-off-by: Igor Stoppa <igor.stoppa@xxxxxxxxxx>
CC: Kees Cook <keescook@xxxxxxxxxxxx>
CC: Chris von Recklinghausen <crecklin@xxxxxxxxxx>
CC: linux-mm@xxxxxxxxx
CC: linux-kernel@xxxxxxxxxxxxxxx
---
 include/linux/prmem.h | 24 ++++++++++++++++++++++++
 mm/usercopy.c         |  5 +++++
 2 files changed, 29 insertions(+)

diff --git a/include/linux/prmem.h b/include/linux/prmem.h
index cf713fc1c8bb..919d853ddc15 100644
--- a/include/linux/prmem.h
+++ b/include/linux/prmem.h
@@ -273,6 +273,30 @@ struct pmalloc_pool {
 	uint8_t mode;
 };
 
+void __noreturn usercopy_abort(const char *name, const char *detail,
+			       bool to_user, unsigned long offset,
+			       unsigned long len);
+
+/**
+ * check_pmalloc_object() - helper for hardened usercopy
+ * @ptr: the beginning of the memory to check
+ * @n: the size of the memory to check
+ * @to_user: copy to userspace or from userspace
+ *
+ * If the check is ok, it will fall-through, otherwise it will abort.
+ * The function is inlined, to minimize the performance impact of the
+ * extra check that can end up on a hot path.
+ * Non-exhaustive micro benchmarking with QEMU x86_64 shows a reduction of
+ * the time spent in this fragment by 60%, when inlined.
+ */
+static inline
+void check_pmalloc_object(const void *ptr, unsigned long n, bool to_user)
+{
+	if (unlikely(__is_wr_after_init(ptr, n) || __is_wr_pool(ptr, n)))
+		usercopy_abort("pmalloc", "accessing pmalloc obj", to_user,
+			       (const unsigned long)ptr, n);
+}
+
 /*
  * The write rare functionality is fully implemented as __always_inline,
  * to prevent having an internal function call that is capable of modifying
diff --git a/mm/usercopy.c b/mm/usercopy.c
index 852eb4e53f06..a080dd37b684 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -22,8 +22,10 @@
 #include <linux/thread_info.h>
 #include <linux/atomic.h>
 #include <linux/jump_label.h>
+#include <linux/prmem.h>
 #include <asm/sections.h>
 
+
 /*
  * Checks if a given pointer and length is contained by the current
  * stack frame (if possible).
@@ -284,6 +286,9 @@ void __check_object_size(const void *ptr, unsigned long n, bool to_user)
 
 	/* Check for object in kernel to avoid text exposure. */
 	check_kernel_text_object((const unsigned long)ptr, n, to_user);
+
+	/* Check if object is from a pmalloc chunk. */
+	check_pmalloc_object(ptr, n, to_user);
 }
 EXPORT_SYMBOL(__check_object_size);
 
-- 
2.17.1