This is a note to let you know that I've just added the patch titled
x86/tls: Don't validate lm in set_thread_area() after all
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-tls-don-t-validate-lm-in-set_thread_area-after-all.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 <[email protected]> know about it.
>From 3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0 Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <[email protected]>
Date: Wed, 17 Dec 2014 14:48:30 -0800
Subject: x86/tls: Don't validate lm in set_thread_area() after all
From: Andy Lutomirski <[email protected]>
commit 3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0 upstream.
It turns out that there's a lurking ABI issue. GCC, when
compiling this in a 32-bit program:
struct user_desc desc = {
.entry_number = idx,
.base_addr = base,
.limit = 0xfffff,
.seg_32bit = 1,
.contents = 0, /* Data, grow-up */
.read_exec_only = 0,
.limit_in_pages = 1,
.seg_not_present = 0,
.useable = 0,
};
will leave .lm uninitialized. This means that anything in the
kernel that reads user_desc.lm for 32-bit tasks is unreliable.
Revert the .lm check in set_thread_area(). The value never did
anything in the first place.
Fixes: 0e58af4e1d21 ("x86/tls: Disallow unusual TLS segments")
Signed-off-by: Andy Lutomirski <[email protected]>
Acked-by: Thomas Gleixner <[email protected]>
Cc: Linus Torvalds <[email protected]>
Link:
http://lkml.kernel.org/r/d7875b60e28c512f6a6fc0baf5714d58e7eaadbb.1418856405.git.l...@amacapital.net
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
arch/x86/include/uapi/asm/ldt.h | 7 +++++++
arch/x86/kernel/tls.c | 6 ------
2 files changed, 7 insertions(+), 6 deletions(-)
--- a/arch/x86/include/uapi/asm/ldt.h
+++ b/arch/x86/include/uapi/asm/ldt.h
@@ -28,6 +28,13 @@ struct user_desc {
unsigned int seg_not_present:1;
unsigned int useable:1;
#ifdef __x86_64__
+ /*
+ * Because this bit is not present in 32-bit user code, user
+ * programs can pass uninitialized values here. Therefore, in
+ * any context in which a user_desc comes from a 32-bit program,
+ * the kernel must act as though lm == 0, regardless of the
+ * actual value.
+ */
unsigned int lm:1;
#endif
};
--- a/arch/x86/kernel/tls.c
+++ b/arch/x86/kernel/tls.c
@@ -55,12 +55,6 @@ static bool tls_desc_okay(const struct u
if (info->seg_not_present)
return false;
-#ifdef CONFIG_X86_64
- /* The L bit makes no sense for data. */
- if (info->lm)
- return false;
-#endif
-
return true;
}
Patches currently in stable-queue which might be from [email protected] are
queue-3.14/x86_64-switch_to-load-tls-descriptors-before-switching-ds-and-es.patch
queue-3.14/x86-tls-disallow-unusual-tls-segments.patch
queue-3.14/x86-tls-validate-tls-entries-to-protect-espfix.patch
queue-3.14/x86-tls-don-t-validate-lm-in-set_thread_area-after-all.patch
queue-3.14/x86-kvm-clear-paravirt_enabled-on-kvm-guests-for-espfix32-s-benefit.patch
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