On Wed, 26 Jun 2019, Dianzhang Chen wrote:
> 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 idx can be controlled from:
> ptrace -> arch_ptrace -> do_get_thread_area.
>
> Fix this by sanitizing idx before using it to index p->thread.tls_array.
Just that I can't find a place which sanitizes the value....
> +#include <linux/nospec.h>
and nothing which uses anything from this header file.
> #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 +229,9 @@ 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;
> +
> + fill_user_desc(&info, idx, &p->thread.tls_array[index]);
So this is just a cosmetic change and the compiler will create probably
exactly the same binary.
Thanks,
tglx
