Re: [PATCH 2/2] x86: fix __user annotations

Jann Horn
2019-04-01T15:04:30Z

On Mon, Apr 1, 2019 at 4:36 PM David Laight <David.Laight@aculab.com> wrote:
>
> From: Jann Horn
> > Sent: 28 March 2019 21:23
> > Fix __user annotations in various places across the x86 tree:
> >
> ...
> > - generic_load_microcode() deals with a pointer that can be either a
> > kernel pointer or a user pointer; change the code to pass it around as
> > a __user pointer, and add explicit casts to convert between __user and
> > __kernel
> ...
> > -static int get_ucode_fw(void *to, const void *from, size_t n)
> > +static int get_ucode_fw(void *to, const void __user *from, size_t n)
> > {
> > - memcpy(to, from, n);
> > + /* cast paired with request_microcode_fw() */
> > + memcpy(to, (const void __force *)from, n);
> > return 0;
> > }
> >
> > @@ -993,7 +996,8 @@ static enum ucode_state request_microcode_fw(int cpu, struct device *device,
> > return UCODE_NFOUND;
> > }
> >
> > - ret = generic_load_microcode(cpu, (void *)firmware->data,
> > + /* cast paired with get_ucode_fw() */
> > + ret = generic_load_microcode(cpu, (void __force __user *)firmware->data,
> > firmware->size, &get_ucode_fw);
> >
> > release_firmware(firmware);
> > @@ -1001,7 +1005,7 @@ static enum ucode_state request_microcode_fw(int cpu, struct device *device,
> > return ret;
> > }
> >
> > -static int get_ucode_user(void *to, const void *from, size_t n)
> > +static int get_ucode_user(void *to, const void __user *from, size_t n)
> > {
> > return copy_from_user(to, from, n);
> > }
> > @@ -1012,7 +1016,7 @@ request_microcode_user(int cpu, const void __user *buf, size_t size)
> > if (is_blacklisted(cpu))
> > return UCODE_NFOUND;
> >
> > - return generic_load_microcode(cpu, (void *)buf, size, &get_ucode_user);
> > + return generic_load_microcode(cpu, buf, size, &get_ucode_user);
>
> That is all an 'accident waiting to happen' ...

What's your suggestion? The code used to store user pointers in
kernel-typed pointers. Now it only stores kernel pointers in
user-typed pointers, which is much less hazardous.