linux-kernel - [PATCH] x86/mm: Set NX on gap between __ex

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Message-Id: <1443704662-3138-1-git-send-email-sds@tycho.nsa.gov>
Date:	Thu,  1 Oct 2015 09:04:22 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	x86@...nel.org
Cc:	linux-kernel@...r.kernel.org, keescook@...omium.org,
	Stephen Smalley <sds@...ho.nsa.gov>
Subject: [PATCH] x86/mm: Set NX on gap between __ex_table and rodata

Unused space between the end of __ex_table and the start of rodata
can be left W+x in the kernel page tables.  Extend the setting
of the NX bit to cover this gap by starting from text_end rather than
rodata_start.

Before:
---[ High Kernel Mapping ]---
0xffffffff80000000-0xffffffff81000000          16M                               pmd
0xffffffff81000000-0xffffffff81600000           6M     ro         PSE     GLB x  pmd
0xffffffff81600000-0xffffffff81754000        1360K     ro                 GLB x  pte
0xffffffff81754000-0xffffffff81800000         688K     RW                 GLB x  pte
0xffffffff81800000-0xffffffff81a00000           2M     ro         PSE     GLB NX pmd
0xffffffff81a00000-0xffffffff81b3b000        1260K     ro                 GLB NX pte
0xffffffff81b3b000-0xffffffff82000000        4884K     RW                 GLB NX pte
0xffffffff82000000-0xffffffff82200000           2M     RW         PSE     GLB NX pmd
0xffffffff82200000-0xffffffffa0000000         478M                               pmd

After:
---[ High Kernel Mapping ]---
0xffffffff80000000-0xffffffff81000000          16M                               pmd
0xffffffff81000000-0xffffffff81600000           6M     ro         PSE     GLB x  pmd
0xffffffff81600000-0xffffffff81754000        1360K     ro                 GLB x  pte
0xffffffff81754000-0xffffffff81800000         688K     RW                 GLB NX pte
0xffffffff81800000-0xffffffff81a00000           2M     ro         PSE     GLB NX pmd
0xffffffff81a00000-0xffffffff81b3b000        1260K     ro                 GLB NX pte
0xffffffff81b3b000-0xffffffff82000000        4884K     RW                 GLB NX pte
0xffffffff82000000-0xffffffff82200000           2M     RW         PSE     GLB NX pmd
0xffffffff82200000-0xffffffffa0000000         478M                               pmd

Signed-off-by: Stephen Smalley <sds@...ho.nsa.gov>
---
 arch/x86/mm/init_64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 30564e2..df48430 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1132,7 +1132,7 @@ void mark_rodata_ro(void)
 	 * has been zapped already via cleanup_highmem().
 	 */
 	all_end = roundup((unsigned long)_brk_end, PMD_SIZE);
-	set_memory_nx(rodata_start, (all_end - rodata_start) >> PAGE_SHIFT);
+	set_memory_nx(text_end, (all_end - text_end) >> PAGE_SHIFT);
 
 	rodata_test();
 
-- 
2.1.0

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