Re: [PATCH] mm: fix RODATA_TEST failure "rodata_test: test data was not read only"
From: Kees Cook <hidden>
Date: 2017-09-24 19:17:54
Also in:
linux-mm, lkml
On Thu, Sep 21, 2017 at 2:37 AM, Christophe Leroy [off-list ref] wrote:
On powerpc, RODATA_TEST fails with message the following messages: [ 6.199505] Freeing unused kernel memory: 528K [ 6.203935] rodata_test: test data was not read only This is because GCC allocates it to .data section: c0695034 g O .data 00000004 rodata_test_data
Uuuh... that seems like a compiler bug. It's marked "const" -- it should never end up in .data. I would argue that this has done exactly what it was supposed to do, and shows that something has gone wrong. It should always be const. Adding "static" should just change visibility. (I'm not opposed to the static change, but it seems to paper over a problem with the compiler...) -Kees
quoted hunk ↗ jump to hunk
Since commit 056b9d8a76924 ("mm: remove rodata_test_data export, add pr_fmt"), rodata_test_data is used only inside rodata_test.c By declaring it static, it gets properly allocated into .rodata section instead of .data: c04df710 l O .rodata 00000004 rodata_test_data Signed-off-by: Christophe Leroy <redacted> --- mm/rodata_test.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/mm/rodata_test.c b/mm/rodata_test.c index 6bb4deb12e78..d908c8769b48 100644 --- a/mm/rodata_test.c +++ b/mm/rodata_test.c@@ -14,7 +14,7 @@ #include <linux/uaccess.h> #include <asm/sections.h> -const int rodata_test_data = 0xC3; +static const int rodata_test_data = 0xC3; void rodata_test(void) { --2.13.3
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