Commit 51d6ca37 authored by Thomas Weißschuh's avatar Thomas Weißschuh Committed by Thomas Gleixner
Browse files

vdso: Add generic random data storage 



Extend the generic vDSO data storage with a page for the random state data.
The random state data is stored in a dedicated page, as the existing
storage page is only meant for time-related, time-namespace-aware data.
This simplifies to access logic to not need to handle time namespaces
anymore and also frees up more space in the time-related page.

In case further generic vDSO data store is required it can be added to
the random state page.

Signed-off-by: default avatarThomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250204-vdso-store-rng-v3-6-13a4669dfc8c@linutronix.de
parent df7fcbef

drivers/char/random.c

+3 −3
Original line number Diff line number Diff line
@@ -278,7 +278,7 @@ static void crng_reseed(struct work_struct *work) 
	WRITE_ONCE(base_crng.generation, next_gen);

#ifdef CONFIG_VDSO_GETRANDOM

	/* base_crng.generation's invalid value is ULONG_MAX, while

	 * _vdso_rng_data.generation's invalid value is 0, so add one to the

	 * vdso_k_rng_data->generation's invalid value is 0, so add one to the

	 * former to arrive at the latter. Use smp_store_release so that this

	 * is ordered with the write above to base_crng.generation. Pairs with

	 * the smp_rmb() before the syscall in the vDSO code.
@@ -290,7 +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 *)&__arch_get_k_vdso_rng_data()->generation, next_gen + 1);

	smp_store_release((unsigned long *)&vdso_k_rng_data->generation, next_gen + 1);

#endif

	if (!static_branch_likely(&crng_is_ready))

		crng_init = CRNG_READY;
@@ -743,7 +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(__arch_get_k_vdso_rng_data()->is_ready, true);

		WRITE_ONCE(vdso_k_rng_data->is_ready, true);

#endif

		wake_up_interruptible(&crng_init_wait);

		kill_fasync(&fasync, SIGIO, POLL_IN);

include/asm-generic/vdso/vsyscall.h

+12 −0
Original line number Diff line number Diff line
@@ -13,6 +13,13 @@ static __always_inline const struct vdso_time_data *__arch_get_vdso_u_time_data( 
}

#endif



#ifndef __arch_get_vdso_u_rng_data

static __always_inline const struct vdso_rng_data *__arch_get_vdso_u_rng_data(void)

{

	return &vdso_u_rng_data;

}

#endif



#else  /* !CONFIG_GENERIC_VDSO_DATA_STORE */



#ifndef __arch_get_k_vdso_data
@@ -25,6 +32,11 @@ static __always_inline struct vdso_data *__arch_get_k_vdso_data(void) 


#define __arch_get_vdso_u_time_data __arch_get_vdso_data



#ifndef __arch_get_vdso_u_rng_data

#define __arch_get_vdso_u_rng_data() __arch_get_vdso_rng_data()

#endif

#define vdso_k_rng_data __arch_get_k_vdso_rng_data()



#endif /* CONFIG_GENERIC_VDSO_DATA_STORE */



#ifndef __arch_update_vsyscall

include/vdso/datapage.h

+10 −0
Original line number Diff line number Diff line
@@ -144,8 +144,10 @@ extern struct vdso_time_data _timens_data[CS_BASES] __attribute__((visibility("h 
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_time_data *vdso_k_time_data;

extern struct vdso_rng_data *vdso_k_rng_data;

#endif



/**
@@ -161,6 +163,7 @@ union vdso_data_store { 
enum vdso_pages {

	VDSO_TIME_PAGE_OFFSET,

	VDSO_TIMENS_PAGE_OFFSET,

	VDSO_RNG_PAGE_OFFSET,

	VDSO_NR_PAGES

};
@@ -184,9 +187,16 @@ enum vdso_pages { 


#else /* !__ASSEMBLY__ */



#ifdef CONFIG_VDSO_GETRANDOM

#define __vdso_u_rng_data	PROVIDE(vdso_u_rng_data = vdso_u_data + 2 * PAGE_SIZE);

#else

#define __vdso_u_rng_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					\





#endif /* !__ASSEMBLY__ */

lib/vdso/datastore.c

+14 −0
Original line number Diff line number Diff line
@@ -17,6 +17,15 @@ struct vdso_time_data *vdso_k_time_data = vdso_time_data_store.data; 
static_assert(sizeof(vdso_time_data_store) == PAGE_SIZE);

#endif /* CONFIG_HAVE_GENERIC_VDSO */



#ifdef CONFIG_VDSO_GETRANDOM

static union {

	struct vdso_rng_data	data;

	u8			page[PAGE_SIZE];

} vdso_rng_data_store __page_aligned_data;

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 */



static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,

			     struct vm_area_struct *vma, struct vm_fault *vmf)

{
@@ -53,6 +62,11 @@ static vm_fault_t vvar_fault(const struct vm_special_mapping *sm, 
			return VM_FAULT_SIGBUS;

		pfn = __phys_to_pfn(__pa_symbol(vdso_k_time_data));

		break;

	case VDSO_RNG_PAGE_OFFSET:

		if (!IS_ENABLED(CONFIG_VDSO_GETRANDOM))

			return VM_FAULT_SIGBUS;

		pfn = __phys_to_pfn(__pa_symbol(vdso_k_rng_data));

		break;

	default:

		return VM_FAULT_SIGBUS;

	}

lib/vdso/getrandom.c

+6 −2
Original line number Diff line number Diff line
@@ -12,6 +12,9 @@ 
#include <uapi/linux/mman.h>

#include <uapi/linux/random.h>



/* Bring in default accessors */

#include <vdso/vsyscall.h>



#undef PAGE_SIZE

#undef PAGE_MASK

#define PAGE_SIZE (1UL << CONFIG_PAGE_SHIFT)
@@ -152,7 +155,7 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_ 


		/*

		 * Prevent the syscall from being reordered wrt current_generation. Pairs with the

		 * smp_store_release(&_vdso_rng_data.generation) in random.c.

		 * smp_store_release(&vdso_k_rng_data->generation) in random.c.

		 */

		smp_rmb();
@@ -256,5 +259,6 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_ 
static __always_inline ssize_t

__cvdso_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state, size_t opaque_len)

{

	return __cvdso_getrandom_data(__arch_get_vdso_rng_data(), buffer, len, flags, opaque_state, opaque_len);

	return __cvdso_getrandom_data(__arch_get_vdso_u_rng_data(), buffer, len, flags,

				      opaque_state, opaque_len);

}