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From: Andy Lutomirski <luto@amacapital.net>
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Date: Thu, 4 Dec 2014 16:48:16 -0800
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Subject: [PATCH] x86/tls: Validate TLS entries to protect espfix
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Installing a 16-bit RW data segment into the GDT defeats espfix.
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AFAICT this will not affect glibc, Wine, or dosemu at all.
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Signed-off-by: Andy Lutomirski <luto@amacapital.net>
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Acked-by: H. Peter Anvin <hpa@zytor.com>
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Cc: stable@vger.kernel.org
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Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Cc: security@kernel.org <security@kernel.org>
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Cc: Willy Tarreau <w@1wt.eu>
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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---
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arch/x86/kernel/tls.c | 23 +++++++++++++++++++++++
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1 file changed, 23 insertions(+)
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diff --git a/arch/x86/kernel/tls.c b/arch/x86/kernel/tls.c
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index f7fec09e3e3a..e7650bd71109 100644
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--- a/arch/x86/kernel/tls.c
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+++ b/arch/x86/kernel/tls.c
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@@ -27,6 +27,21 @@ static int get_free_idx(void)
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return -ESRCH;
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}
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+static bool tls_desc_okay(const struct user_desc *info)
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+{
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+ if (LDT_empty(info))
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+ return true;
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+
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+ /*
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+ * espfix is required for 16-bit data segments, but espfix
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+ * only works for LDT segments.
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+ */
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+ if (!info->seg_32bit)
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+ return false;
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+
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+ return true;
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+}
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+
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static void set_tls_desc(struct task_struct *p, int idx,
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const struct user_desc *info, int n)
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{
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@@ -66,6 +81,9 @@ int do_set_thread_area(struct task_struct *p, int idx,
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if (copy_from_user(&info, u_info, sizeof(info)))
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return -EFAULT;
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+ if (!tls_desc_okay(&info))
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+ return -EINVAL;
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+
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if (idx == -1)
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idx = info.entry_number;
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@@ -192,6 +210,7 @@ int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
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{
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struct user_desc infobuf[GDT_ENTRY_TLS_ENTRIES];
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const struct user_desc *info;
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+ int i;
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if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
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(pos % sizeof(struct user_desc)) != 0 ||
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@@ -205,6 +224,10 @@ int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
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else
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info = infobuf;
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+ for (i = 0; i < count / sizeof(struct user_desc); i++)
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+ if (!tls_desc_okay(info + i))
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+ return -EINVAL;
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+
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set_tls_desc(target,
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GDT_ENTRY_TLS_MIN + (pos / sizeof(struct user_desc)),
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info, count / sizeof(struct user_desc));
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--
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2.1.0
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