Commit 30a9b8b4 authored by Dianzhang Chen's avatar Dianzhang Chen Committed by Greg Kroah-Hartman

x86/tls: Fix possible spectre-v1 in do_get_thread_area()

commit 993773d11d45c90cb1c6481c2638c3d9f092ea5b upstream.

The index to access the threads tls array is controlled by userspace
via syscall: sys_ptrace(), hence leading to a potential exploitation
of the Spectre variant 1 vulnerability.

The index can be controlled from:
        ptrace -> arch_ptrace -> do_get_thread_area.

Fix this by sanitizing the user supplied index before using it to access
the p->thread.tls_array.
Signed-off-by: default avatarDianzhang Chen <dianzhangchen0@gmail.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1561524630-3642-1-git-send-email-dianzhangchen0@gmail.comSigned-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent f41c1f4e
......@@ -5,6 +5,7 @@
#include <linux/user.h>
#include <linux/regset.h>
#include <linux/syscalls.h>
#include <linux/nospec.h>
#include <linux/uaccess.h>
#include <asm/desc.h>
......@@ -220,6 +221,7 @@ int do_get_thread_area(struct task_struct *p, int idx,
struct user_desc __user *u_info)
{
struct user_desc info;
int index;
if (idx == -1 && get_user(idx, &u_info->entry_number))
return -EFAULT;
......@@ -227,8 +229,11 @@ int do_get_thread_area(struct task_struct *p, int idx,
if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
return -EINVAL;
fill_user_desc(&info, idx,
&p->thread.tls_array[idx - GDT_ENTRY_TLS_MIN]);
index = idx - GDT_ENTRY_TLS_MIN;
index = array_index_nospec(index,
GDT_ENTRY_TLS_MAX - GDT_ENTRY_TLS_MIN + 1);
fill_user_desc(&info, idx, &p->thread.tls_array[index]);
if (copy_to_user(u_info, &info, sizeof(info)))
return -EFAULT;
......
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