[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <1398197671-12786-132-git-send-email-kamal@canonical.com>
Date: Tue, 22 Apr 2014 13:14:29 -0700
From: Kamal Mostafa <kamal@...onical.com>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
kernel-team@...ts.ubuntu.com
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
"H. Peter Anvin" <hpa@...ux.intel.com>,
Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.8 131/133] x86-64, modify_ldt: Ban 16-bit segments on 64-bit kernels
3.8.13.22 -stable review patch. If anyone has any objections, please let me know.
------------------
From: "H. Peter Anvin" <hpa@...ux.intel.com>
commit b3b42ac2cbae1f3cecbb6229964a4d48af31d382 upstream.
The IRET instruction, when returning to a 16-bit segment, only
restores the bottom 16 bits of the user space stack pointer. We have
a software workaround for that ("espfix") for the 32-bit kernel, but
it relies on a nonzero stack segment base which is not available in
32-bit mode.
Since 16-bit support is somewhat crippled anyway on a 64-bit kernel
(no V86 mode), and most (if not quite all) 64-bit processors support
virtualization for the users who really need it, simply reject
attempts at creating a 16-bit segment when running on top of a 64-bit
kernel.
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
Link: http://lkml.kernel.org/n/tip-kicdm89kzw9lldryb1br9od0@git.kernel.org
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
arch/x86/kernel/ldt.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index ebc9873..af1d14a 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -229,6 +229,17 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
}
}
+ /*
+ * On x86-64 we do not support 16-bit segments due to
+ * IRET leaking the high bits of the kernel stack address.
+ */
+#ifdef CONFIG_X86_64
+ if (!ldt_info.seg_32bit) {
+ error = -EINVAL;
+ goto out_unlock;
+ }
+#endif
+
fill_ldt(&ldt, &ldt_info);
if (oldmode)
ldt.avl = 0;
--
1.9.1
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists