linux-kernel - [PATCH] modules: always page-align module section allocations

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Date:   Wed, 24 Jul 2019 17:01:56 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        Yang Yingliang <yangyingliang@...wei.com>,
        Jian Cheng <cj.chengjian@...wei.com>,
        Nadav Amit <namit@...are.com>, Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...nel.org>,
        David Lechner <david@...hnology.com>,
        Adam Ford <aford173@...il.com>,
        Martin Kaiser <lists@...ser.cx>, Jessica Yu <jeyu@...nel.org>
Subject: [PATCH] modules: always page-align module section allocations

Some arches (e.g., arm64, x86) have moved towards non-executable
module_alloc() allocations for security hardening reasons. That means
that the module loader will need to set the text section of a module to
executable, regardless of whether or not CONFIG_STRICT_MODULE_RWX is set.

When CONFIG_STRICT_MODULE_RWX=y, module section allocations are always
page-aligned to handle memory rwx permissions. On some arches with
CONFIG_STRICT_MODULE_RWX=n however, when setting the module text to
executable, the BUG_ON() in frob_text() gets triggered since module
section allocations are not page-aligned when CONFIG_STRICT_MODULE_RWX=n.
Since the set_memory_* API works with pages, and since we need to call
set_memory_x() regardless of whether CONFIG_STRICT_MODULE_RWX is set, we
might as well page-align all module section allocations for ease of
managing rwx permissions of module sections (text, rodata, etc).

Fixes: 2eef1399a866 ("modules: fix BUG when load module with rodata=n")
Reported-by: Martin Kaiser <lists@...ser.cx>
Reported-by: Bartosz Golaszewski <brgl@...ev.pl>
Tested-by: David Lechner <david@...hnology.com>
Tested-by: Martin Kaiser <martin@...ser.cx>
Signed-off-by: Jessica Yu <jeyu@...nel.org>
---
 kernel/module.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 5933395af9a0..cd8df516666d 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -64,14 +64,9 @@

 /*
  * Modules' sections will be aligned on page boundaries
- * to ensure complete separation of code and data, but
- * only when CONFIG_STRICT_MODULE_RWX=y
+ * to ensure complete separation of code and data
  */
-#ifdef CONFIG_STRICT_MODULE_RWX
 # define debug_align(X) ALIGN(X, PAGE_SIZE)
-#else
-# define debug_align(X) (X)
-#endif

 /* If this is set, the section belongs in the init part of the module */
 #define INIT_OFFSET_MASK (1UL << (BITS_PER_LONG-1))
-- 
2.16.4