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

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Date:   Tue, 30 Jul 2019 10:42:39 +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>
Subject: Re: [PATCH] modules: always page-align module section allocations

+++ Jessica Yu [24/07/19 17:01 +0200]:
>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>

Applied, thanks everyone for testing.

> 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
>