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x86/tls: Validate TLS entries to protect espfix

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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: stable@vger.kernel.org
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>
This commit is contained in:
Andy Lutomirski 2014-12-04 16:48:16 -08:00 committed by Ingo Molnar
parent f0905c5a32
commit 41bdc78544
1 changed files with 23 additions and 0 deletions
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23
arch/x86/kernel/tls.c
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@ -27,6 +27,21 @@ 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)
{
@ -66,6 +81,9 @@ int do_set_thread_area(struct task_struct *p, int idx,
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;
@ -192,6 +210,7 @@ int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
{
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 ||
@ -205,6 +224,10 @@ int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
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));