vdso: Add generic architecture-specific data storage

Some architectures need to expose architecture-specific data to the vDSO.

Enable the generic vDSO storage mechanism to both store and map this
data. Some architectures require more than a single page, like LoongArch,
so prepare for that usecase, too.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250204-vdso-store-rng-v3-7-13a4669dfc8c@linutronix.de

Author: t-8ch

arch/Kconfig

@@ -1584,6 +1584,10 @@ config HAVE_SPARSE_SYSCALL_NR
 	  entries at 4000, 5000 and 6000 locations. This option turns on syscall
 	  related optimizations for a given architecture.
 
+config ARCH_HAS_VDSO_ARCH_DATA
+	depends on GENERIC_VDSO_DATA_STORE
+	bool
+
 config ARCH_HAS_VDSO_TIME_DATA
 	bool
 

include/vdso/datapage.h

@@ -9,11 +9,13 @@
 #include <uapi/linux/types.h>
 #include <uapi/asm-generic/errno-base.h>
 
+#include <vdso/align.h>
 #include <vdso/bits.h>
 #include <vdso/clocksource.h>
 #include <vdso/ktime.h>
 #include <vdso/limits.h>
 #include <vdso/math64.h>
+#include <vdso/page.h>
 #include <vdso/processor.h>
 #include <vdso/time.h>
 #include <vdso/time32.h>
@@ -25,6 +27,15 @@
 struct arch_vdso_time_data {};
 #endif
 
+#if defined(CONFIG_ARCH_HAS_VDSO_ARCH_DATA)
+#include <asm/vdso/arch_data.h>
+#elif defined(CONFIG_GENERIC_VDSO_DATA_STORE)
+struct vdso_arch_data {
+	/* Needed for the generic code, never actually used at runtime */
+	char __unused;
+};
+#endif
+
 #define VDSO_BASES	(CLOCK_TAI + 1)
 #define VDSO_HRES	(BIT(CLOCK_REALTIME)		| \
 			 BIT(CLOCK_MONOTONIC)		| \
@@ -145,9 +156,11 @@ extern struct vdso_rng_data _vdso_rng_data __attribute__((visibility("hidden")))
 #else
 extern struct vdso_time_data vdso_u_time_data[CS_BASES] __attribute__((visibility("hidden")));
 extern struct vdso_rng_data vdso_u_rng_data __attribute__((visibility("hidden")));
+extern struct vdso_arch_data vdso_u_arch_data __attribute__((visibility("hidden")));
 
 extern struct vdso_time_data *vdso_k_time_data;
 extern struct vdso_rng_data *vdso_k_rng_data;
+extern struct vdso_arch_data *vdso_k_arch_data;
 #endif
 
 /**
@@ -160,10 +173,15 @@ union vdso_data_store {
 
 #ifdef CONFIG_GENERIC_VDSO_DATA_STORE
 
+#define VDSO_ARCH_DATA_SIZE ALIGN(sizeof(struct vdso_arch_data), PAGE_SIZE)
+#define VDSO_ARCH_DATA_PAGES (VDSO_ARCH_DATA_SIZE >> PAGE_SHIFT)
+
 enum vdso_pages {
 	VDSO_TIME_PAGE_OFFSET,
 	VDSO_TIMENS_PAGE_OFFSET,
 	VDSO_RNG_PAGE_OFFSET,
+	VDSO_ARCH_PAGES_START,
+	VDSO_ARCH_PAGES_END = VDSO_ARCH_PAGES_START + VDSO_ARCH_DATA_PAGES - 1,
 	VDSO_NR_PAGES
 };
 
@@ -193,10 +211,17 @@ enum vdso_pages {
 #define __vdso_u_rng_data
 #endif
 
+#ifdef CONFIG_ARCH_HAS_VDSO_ARCH_DATA
+#define __vdso_u_arch_data	PROVIDE(vdso_u_arch_data = vdso_u_data + 3 * PAGE_SIZE);
+#else
+#define __vdso_u_arch_data
+#endif
+
 #define VDSO_VVAR_SYMS						\
 	PROVIDE(vdso_u_data = . - __VDSO_PAGES * PAGE_SIZE);	\
 	PROVIDE(vdso_u_time_data = vdso_u_data);		\
 	__vdso_u_rng_data					\
+	__vdso_u_arch_data					\
 
 
 #endif /* !__ASSEMBLY__ */

lib/vdso/datastore.c

@@ -26,6 +26,14 @@ struct vdso_rng_data *vdso_k_rng_data = &vdso_rng_data_store.data;
 static_assert(sizeof(vdso_rng_data_store) == PAGE_SIZE);
 #endif /* CONFIG_VDSO_GETRANDOM */
 
+#ifdef CONFIG_ARCH_HAS_VDSO_ARCH_DATA
+static union {
+	struct vdso_arch_data	data;
+	u8			page[VDSO_ARCH_DATA_SIZE];
+} vdso_arch_data_store __page_aligned_data;
+struct vdso_arch_data *vdso_k_arch_data = &vdso_arch_data_store.data;
+#endif /* CONFIG_ARCH_HAS_VDSO_ARCH_DATA */
+
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
 			     struct vm_area_struct *vma, struct vm_fault *vmf)
 {
@@ -67,6 +75,12 @@ static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
 			return VM_FAULT_SIGBUS;
 		pfn = __phys_to_pfn(__pa_symbol(vdso_k_rng_data));
 		break;
+	case VDSO_ARCH_PAGES_START ... VDSO_ARCH_PAGES_END:
+		if (!IS_ENABLED(CONFIG_ARCH_HAS_VDSO_ARCH_DATA))
+			return VM_FAULT_SIGBUS;
+		pfn = __phys_to_pfn(__pa_symbol(vdso_k_arch_data)) +
+			vmf->pgoff - VDSO_ARCH_PAGES_START;
+		break;
 	default:
 		return VM_FAULT_SIGBUS;
 	}