Messages in this thread | ![/](/images/icornerl.gif) | | Date | Sun, 23 Jun 2019 13:47:59 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH] x86: fix possible spectre-v1 in do_get_thread_area() |
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On Fri, 24 May 2019, Dianzhang Chen wrote:
> The idx in do_get_thread_area() is controlled by userspace via syscall: ptrace(defined in kernel/ptrace.c), 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. > > Signed-off-by: Dianzhang Chen <dianzhangchen0@gmail.com> > --- > arch/x86/kernel/tls.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/tls.c b/arch/x86/kernel/tls.c > index a5b802a..e3dc05b 100644 > --- 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> > @@ -220,15 +221,19 @@ int do_get_thread_area(struct task_struct *p, int idx, > struct user_desc __user *u_info) > { > struct user_desc info; > + int index = idx - GDT_ENTRY_TLS_MIN; > > if (idx == -1 && get_user(idx, &u_info->entry_number)) > return -EFAULT;
This is broken in case of idx == -1 because index is not reevaluated after idx is copied from u_info. You have to calculate index _AFTER_ that.
> - if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX) > + if (index < 0 || index > GDT_ENTRY_TLS_MAX - GDT_ENTRY_TLS_MIN) > return -EINVAL; > > + index = array_index_nospec(index, > + GDT_ENTRY_TLS_MAX - GDT_ENTRY_TLS_MIN + 1);
What about defining the array size and using it here and in the sanity check above?
> + > fill_user_desc(&info, idx, > - &p->thread.tls_array[idx - GDT_ENTRY_TLS_MIN]); > + &p->thread.tls_array[index]);
Please get rid of the line break. The line now fits into 80 char.
Thanks,
tglx
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