Re: [PATCH v10 3/4] random: introduce generic vDSO getrandom() implementation

Jason A. Donenfeld
2022-11-30T15:01:49Z

On Wed, Nov 30, 2022 at 03:51:01PM +0100, Jason A. Donenfeld wrote:
> Hi Florian,
>
> On Wed, Nov 30, 2022 at 11:44:30AM +0100, Florian Weimer wrote:
> > * Jason A. Donenfeld:
> >
> > > diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h
> > > index 73eb622e7663..9ae4d76b36c7 100644
> > > --- a/include/vdso/datapage.h
> > > +++ b/include/vdso/datapage.h
> > > @@ -109,6 +109,16 @@ struct vdso_data {
> > > struct arch_vdso_data arch_data;
> > > };
> > >
> > > +/**
> > > + * struct vdso_rng_data - vdso RNG state information
> > > + * @generation: a counter representing the number of RNG reseeds
> > > + * @is_ready: whether the RNG is initialized
> > > + */
> > > +struct vdso_rng_data {
> > > + unsigned long generation;
> > > + bool is_ready;
> > > +};
> > > +
> >
> > I don't think you can use a type like long here. The header says this:
> >
> > * vdso_data will be accessed by 64 bit and compat code at the same time
> > * so we should be careful before modifying this structure.
> >
> > So the ABI must be same for 32-bit and 64-bit mode, and long isn't.
>
> Excellent point. The size of the type needs to be explicit. Will fix.

I'll do something like this:

diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h
index 80e25cdcdb1c..218bbeac5613 100644
--- a/include/vdso/datapage.h
+++ b/include/vdso/datapage.h
@@ -19,6 +19,19 @@
#include <vdso/time32.h>
#include <vdso/time64.h>

+/**
+ * type vdso_kernel_ulong - unsigned long type that matches kernel's unsigned long
+ *
+ * The structs in this file must operate the same way in both 64-bit code and
+ * in 32-bit compat code, over the same potentially 64-bit kernel. So, this
+ * type represents the size of an unsigned long as used by kernel-space code.
+ */
+#ifdef CONFIG_64BIT
+typedef u64 vdso_kernel_ulong;
+#else
+typedef u32 vdso_kernel_ulong;
+#endif
+
#ifdef CONFIG_ARCH_HAS_VDSO_DATA
#include <asm/vdso/data.h>
#else
@@ -115,8 +128,8 @@ struct vdso_data {
* @is_ready: signals whether the RNG is initialized
*/
struct vdso_rng_data {
- unsigned long generation;
- bool is_ready;
+ vdso_kernel_ulong generation;
+ bool is_ready;
};

/*