Commit 993773d1 authored by Dianzhang Chen's avatar Dianzhang Chen Committed by Thomas Gleixner
Browse files

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



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.com
parent 31a2fbb3

arch/x86/kernel/tls.c

+7 −2
Original line number Original line Diff line number Diff line
@@ -5,6 +5,7 @@ 
#include <linux/user.h>

#include <linux/user.h>

#include <linux/regset.h>

#include <linux/regset.h>

#include <linux/syscalls.h>

#include <linux/syscalls.h>

#include <linux/nospec.h>





#include <linux/uaccess.h>

#include <linux/uaccess.h>

#include <asm/desc.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 __user *u_info)

{

{

	struct user_desc info;

	struct user_desc info;

	int index;





	if (idx == -1 && get_user(idx, &u_info->entry_number))

	if (idx == -1 && get_user(idx, &u_info->entry_number))

		return -EFAULT;

		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)

	if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)

		return -EINVAL;

		return -EINVAL;





	fill_user_desc(&info, idx,

	index = idx - GDT_ENTRY_TLS_MIN;

		       &p->thread.tls_array[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)))

	if (copy_to_user(u_info, &info, sizeof(info)))

		return -EFAULT;

		return -EFAULT;

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