This is a note to let you know that I've just added the patch titled
x86-64, modify_ldt: Ban 16-bit segments on 64-bit kernels
to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-64-modify_ldt-ban-16-bit-segments-on-64-bit-kernels.patch
and it can be found in the queue-3.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From b3b42ac2cbae1f3cecbb6229964a4d48af31d382 Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa@xxxxxxxxxxxxxxx>
Date: Sun, 16 Mar 2014 15:31:54 -0700
Subject: x86-64, modify_ldt: Ban 16-bit segments on 64-bit kernels
From: "H. Peter Anvin" <hpa@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-kicdm89kzw9lldryb1br9od0@xxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/ldt.c | 11 +++++++++++
1 file changed, 11 insertions(+)
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -229,6 +229,17 @@ static int write_ldt(void __user *ptr, u
}
}
+ /*
+ * 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;
Patches currently in stable-queue which might be from hpa@xxxxxxxxxxxxxxx are
queue-3.14/ftrace-x86-one-more-missing-sync-after-fixup-of-function-modification-failure.patch
queue-3.14/x86-avx-512-enable-avx-512-states-context-switch.patch
queue-3.14/x86-hash-fix-build-failure-with-older-binutils.patch
queue-3.14/x86-avx-512-avx-512-feature-detection.patch
queue-3.14/x86-64-modify_ldt-ban-16-bit-segments-on-64-bit-kernels.patch
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