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Subject[PATCH 3.2 10/27] x86/tls: Validate TLS entries to protect espfix
3.2.66-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Lutomirski <luto@amacapital.net>

commit 41bdc78544b8a93a9c6814b8bbbfef966272abbe upstream.

Installing a 16-bit RW data segment into the GDT defeats espfix.
AFAICT this will not affect glibc, Wine, or dosemu at all.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: security@kernel.org <security@kernel.org>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/x86/kernel/tls.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

--- a/arch/x86/kernel/tls.c
+++ b/arch/x86/kernel/tls.c
@@ -28,6 +28,21 @@ static int get_free_idx(void)
return -ESRCH;
}

+static bool tls_desc_okay(const struct user_desc *info)
+{
+ if (LDT_empty(info))
+ return true;
+
+ /*
+ * espfix is required for 16-bit data segments, but espfix
+ * only works for LDT segments.
+ */
+ if (!info->seg_32bit)
+ return false;
+
+ return true;
+}
+
static void set_tls_desc(struct task_struct *p, int idx,
const struct user_desc *info, int n)
{
@@ -67,6 +82,9 @@ int do_set_thread_area(struct task_struc
if (copy_from_user(&info, u_info, sizeof(info)))
return -EFAULT;

+ if (!tls_desc_okay(&info))
+ return -EINVAL;
+
if (idx == -1)
idx = info.entry_number;

@@ -197,6 +215,7 @@ int regset_tls_set(struct task_struct *t
{
struct user_desc infobuf[GDT_ENTRY_TLS_ENTRIES];
const struct user_desc *info;
+ int i;

if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
(pos % sizeof(struct user_desc)) != 0 ||
@@ -210,6 +229,10 @@ int regset_tls_set(struct task_struct *t
else
info = infobuf;

+ for (i = 0; i < count / sizeof(struct user_desc); i++)
+ if (!tls_desc_okay(info + i))
+ return -EINVAL;
+
set_tls_desc(target,
GDT_ENTRY_TLS_MIN + (pos / sizeof(struct user_desc)),
info, count / sizeof(struct user_desc));


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