From: Dianzhang Chen dianzhangchen0@gmail.com
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: Dianzhang Chen dianzhangchen0@gmail.com Signed-off-by: Thomas 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@gm... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/tls.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
--- a/arch/x86/kernel/tls.c +++ b/arch/x86/kernel/tls.c @@ -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_struc 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_struc 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;