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vdso: Add generic random data storage

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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: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250204-vdso-store-rng-v3-6-13a4669dfc8c@linutronix.de
This commit is contained in:
Thomas Weißschuh
2025-02-04 13:05:38 +01:00
committed by Thomas Gleixner
parent df7fcbefa7
commit 51d6ca373f
5 changed files with 45 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
drivers/char/random.c
View File

@@ -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);

12
include/asm-generic/vdso/vsyscall.h
View File

@@ -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

10
include/vdso/datapage.h
View File

@@ -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__ */

14
lib/vdso/datastore.c
View File

@@ -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;
}

8
lib/vdso/getrandom.c
View File

@@ -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 @@ retry_generation:
/*
* 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 @@ fallback_syscall:
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);
}