random: vDSO: add __arch_get_k_vdso_rng_data() helper for data page access

_vdso_data is specific to x86 and __arch_get_k_vdso_data() is provided
so that all architectures can provide the requested pointer.

Do the same with _vdso_rng_data, provide __arch_get_k_vdso_rng_data()
and don't use x86 _vdso_rng_data directly.

Until now vdso/vsyscall.h was only included by time/vsyscall.c but now
it will also be included in char/random.c, leading to a duplicate
declaration of _vdso_data and _vdso_rng_data.

To fix this issue, move the declaration in a C file. vma.c looks like
the most appropriate candidate. We don't need to replace the definitions
in vsyscall.h by declarations as declarations are already in asm/vvar.h.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

arch/x86/entry/vdso/vma.c

@@ -38,6 +38,9 @@ struct vdso_data *arch_get_vdso_data(void *vvar_page)
 }
 #undef EMIT_VVAR
 
+DEFINE_VVAR(struct vdso_data, _vdso_data);
+DEFINE_VVAR_SINGLE(struct vdso_rng_data, _vdso_rng_data);
+
 unsigned int vclocks_used __read_mostly;
 
 #if defined(CONFIG_X86_64)

arch/x86/include/asm/vdso/vsyscall.h

@@ -9,9 +9,6 @@
 #include <asm/vgtod.h>
 #include <asm/vvar.h>
 
-DEFINE_VVAR(struct vdso_data, _vdso_data);
-DEFINE_VVAR_SINGLE(struct vdso_rng_data, _vdso_rng_data);
-
 /*
  * Update the vDSO data page to keep in sync with kernel timekeeping.
  */
@@ -22,6 +19,13 @@ struct vdso_data *__x86_get_k_vdso_data(void)
 }
 #define __arch_get_k_vdso_data __x86_get_k_vdso_data
 
+static __always_inline
+struct vdso_rng_data *__x86_get_k_vdso_rng_data(void)
+{
+	return &_vdso_rng_data;
+}
+#define __arch_get_k_vdso_rng_data __x86_get_k_vdso_rng_data
+
 /* The asm-generic header needs to be included after the definitions above */
 #include <asm-generic/vdso/vsyscall.h>
 

drivers/char/random.c

@@ -59,6 +59,7 @@
 #ifdef CONFIG_VDSO_GETRANDOM
 #include <vdso/getrandom.h>
 #include <vdso/datapage.h>
+#include <vdso/vsyscall.h>
 #endif
 #include <asm/archrandom.h>
 #include <asm/processor.h>
@@ -289,7 +290,7 @@ static void crng_reseed(struct work_struct *work)
 	 * because the vDSO side only checks whether the value changed, without
 	 * actually using or interpreting the value.
 	 */
-	smp_store_release((unsigned long *)&_vdso_rng_data.generation, next_gen + 1);
+	smp_store_release((unsigned long *)&__arch_get_k_vdso_rng_data()->generation, next_gen + 1);
 #endif
 	if (!static_branch_likely(&crng_is_ready))
 		crng_init = CRNG_READY;
@@ -742,7 +743,7 @@ static void __cold _credit_init_bits(size_t bits)
 			queue_work(system_unbound_wq, &set_ready);
 		atomic_notifier_call_chain(&random_ready_notifier, 0, NULL);
 #ifdef CONFIG_VDSO_GETRANDOM
-		WRITE_ONCE(_vdso_rng_data.is_ready, true);
+		WRITE_ONCE(__arch_get_k_vdso_rng_data()->is_ready, true);
 #endif
 		wake_up_interruptible(&crng_init_wait);
 		kill_fasync(&fasync, SIGIO, POLL_IN);