x86/vdso: Access rng vdso data without vvar.h

The vdso_rng_data is at a well-known offset in the vvar page.
Make use of this invariant to remove the usage of vvar.h.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20241010-vdso-generic-base-v1-16-b64f0842d512@linutronix.de

Author: t-8ch

arch/x86/entry/vdso/vdso-layout.lds.S

@@ -24,6 +24,8 @@ SECTIONS
 #include <asm/vvar.h>
 #undef EMIT_VVAR
 
+	vdso_rng_data = vvar_page + __VDSO_RND_DATA_OFFSET;
+
 	pvclock_page = vvar_start + PAGE_SIZE;
 	hvclock_page = vvar_start + 2 * PAGE_SIZE;
 	timens_page  = vvar_start + 3 * PAGE_SIZE;

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

@@ -8,7 +8,6 @@
 #ifndef __ASSEMBLY__
 
 #include <asm/unistd.h>
-#include <asm/vvar.h>
 
 /**
  * getrandom_syscall - Invoke the getrandom() syscall.
@@ -28,13 +27,14 @@ static __always_inline ssize_t getrandom_syscall(void *buffer, size_t len, unsig
 	return ret;
 }
 
-#define __vdso_rng_data (VVAR(_vdso_rng_data))
+extern struct vdso_rng_data vdso_rng_data
+	__attribute__((visibility("hidden")));
 
 static __always_inline const struct vdso_rng_data *__arch_get_vdso_rng_data(void)
 {
 	if (IS_ENABLED(CONFIG_TIME_NS) && __arch_get_vdso_data()->clock_mode == VDSO_CLOCKMODE_TIMENS)
-		return (void *)&__vdso_rng_data + ((void *)&timens_page - (void *)__arch_get_vdso_data());
-	return &__vdso_rng_data;
+		return (void *)&vdso_rng_data + ((void *)&timens_page - (void *)__arch_get_vdso_data());
+	return &vdso_rng_data;
 }
 
 #endif /* !__ASSEMBLY__ */

arch/x86/include/asm/vvar.h

@@ -62,11 +62,6 @@ extern char __vvar_page;
 
 DECLARE_VVAR(0, struct vdso_data, _vdso_data)
 
-#if !defined(_SINGLE_DATA)
-#define _SINGLE_DATA
-DECLARE_VVAR_SINGLE(__VDSO_RND_DATA_OFFSET, struct vdso_rng_data, _vdso_rng_data)
-#endif
-
 #undef DECLARE_VVAR
 #undef DECLARE_VVAR_SINGLE