When memory is lent to the Secure world via FF-A, fatal CPU speculative reads from Non-Secure can still occur as long as it retains a cacheable mapping to that memory. Introduce the "arm,ffa-lend-pool" reserved-memory CMA driver to unmap pages before lending (ffa_prepare_lend()) and restore them upon reclaim (ffa_lend_reclaimed()). Devices bind to the pool via the "memory-region" DT property or via ffa_lend_pool_attach().
reserved-memory { #address-cells = <0x2>; #size-cells = <0x2>; ranges;
ffa_lend: ffa-lend-pool { compatible = "arm,ffa-lend-pool"; reusable; size = <0x0 0x4000000>; }; };
Signed-off-by: Vincent Donnefort vdonnefort@google.com --- drivers/firmware/arm_ffa/Kconfig | 5 + drivers/firmware/arm_ffa/Makefile | 1 + drivers/firmware/arm_ffa/lend_pool.c | 261 +++++++++++++++++++++++++++ include/linux/arm_ffa.h | 23 +++ 4 files changed, 290 insertions(+) create mode 100644 drivers/firmware/arm_ffa/lend_pool.c
diff --git a/drivers/firmware/arm_ffa/Kconfig b/drivers/firmware/arm_ffa/Kconfig index 5e3ae5cf82e8..66dbf74c37c3 100644 --- a/drivers/firmware/arm_ffa/Kconfig +++ b/drivers/firmware/arm_ffa/Kconfig @@ -19,3 +19,8 @@ config ARM_FFA_SMCCC bool default ARM_FFA_TRANSPORT depends on ARM64 && HAVE_ARM_SMCCC_DISCOVERY + +config ARM_FFA_LEND_POOL + bool + default y + depends on ARM_FFA_TRANSPORT && CMA && OF_RESERVED_MEM diff --git a/drivers/firmware/arm_ffa/Makefile b/drivers/firmware/arm_ffa/Makefile index 168990a7e792..5ea3019c407b 100644 --- a/drivers/firmware/arm_ffa/Makefile +++ b/drivers/firmware/arm_ffa/Makefile @@ -6,3 +6,4 @@ ffa-core-objs := $(ffa-bus-y) ffa-module-objs := $(ffa-driver-y) $(ffa-transport-y) obj-$(CONFIG_ARM_FFA_TRANSPORT) = ffa-core.o obj-$(CONFIG_ARM_FFA_TRANSPORT) += ffa-module.o +obj-$(CONFIG_ARM_FFA_LEND_POOL) += lend_pool.o diff --git a/drivers/firmware/arm_ffa/lend_pool.c b/drivers/firmware/arm_ffa/lend_pool.c new file mode 100644 index 000000000000..e4348f5c618b --- /dev/null +++ b/drivers/firmware/arm_ffa/lend_pool.c @@ -0,0 +1,261 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Arm FF-A Reserved Memory CMA driver for Memory Lending + * + * Prevents CPU speculative reads to secure memory by unmapping it from the + * kernel direct map. This works if rodata=full or if all CPUs in the system + * support BBML3 or if a reserved-memory is declared for this driver + * "arm,ffa_lend_pool". + * + * Copyright (C) 2026 Google LLC + * Author: Vincent Donnefort vdonnefort@google.com + */ + +#include <linux/arm_ffa.h> +#include <linux/cleanup.h> +#include <linux/cma.h> +#include <linux/dma-map-ops.h> +#include <linux/init.h> +#include <linux/memblock.h> +#include <linux/mm.h> +#include <linux/of.h> +#include <linux/of_reserved_mem.h> +#include <linux/rcupdate.h> +#include <linux/suspend.h> +#include <linux/set_memory.h> +#include <linux/xarray.h> + +#include <linux/cacheflush.h> +#include <asm/tlbflush.h> + +static DEFINE_XARRAY(ffa_lend_pool_devices); +static atomic_t ffa_lend_pool_active; + +#define FFA_LEND_POOL_DISABLED -1 + +static bool ffa_lend_pool_can_set_direct_map(struct device *dev, struct page *page, u64 nr_pages) +{ + phys_addr_t addr, base, end; + size_t size; + + if (can_set_direct_map()) + return true; + + if (!dev) + return false; + + guard(rcu)(); + + if (xa_load(&ffa_lend_pool_devices, (unsigned long)dev) != dev) + return false; + + if (WARN_ON_ONCE(!dev->cma_area)) + return false; + + addr = page_to_phys(page); + size = nr_pages << PAGE_SHIFT; + base = cma_get_base(dev->cma_area); + end = base + cma_get_size(dev->cma_area); + + return addr >= base && (addr + size) <= end; +} + +/** + * ffa_prepare_lend() - Prepare a memory region to be lent in FF-A + * @dev: Device attached to the lend pool + * @page: First page of the memory region + * @nr_pages: Number of pages + * + * When memory is lent via FF-A, TrustZone transitions it to the secure state. + * As long as Arm CPUs retain a valid mapping to that now-secure memory, they + * can speculatively read it, which is fatal on some systems. + * + * ffa_prepare_lend() prevents this by unmapping the memory range from the + * kernel's direct map. + * + * Return: 0 on success, negative error code otherwise. + */ +int ffa_prepare_lend(struct device *dev, struct page *page, u64 nr_pages) +{ + struct page *p, *end; + unsigned long addr; + int ret; + + if (!ffa_lend_pool_can_set_direct_map(dev, page, nr_pages)) + return -ENODEV; + + /* provides full ordering */ + if (!atomic_add_unless(&ffa_lend_pool_active, 1, FFA_LEND_POOL_DISABLED)) + return -EBUSY; + + end = page + nr_pages; + for (p = page; p < end; p++) + flush_dcache_page(p); + + ret = __set_direct_map_invalid_noflush(page, nr_pages); + if (ret) { + atomic_dec(&ffa_lend_pool_active); + return ret; + } + + addr = (unsigned long)page_address(page); + flush_tlb_kernel_range(addr, addr + (nr_pages << PAGE_SHIFT)); + + return 0; +} +EXPORT_SYMBOL_GPL(ffa_prepare_lend); + +/** + * ffa_lend_reclaimed() - Restore a reclaimed FF-A memory region + * @dev: Device attached to the lend pool + * @page: First page of the memory region + * @nr_pages: Number of pages + * + * Restores a memory range into the kernel's direct mapping. It must be called + * after a successful FF-A memory reclaim invocation. + */ +void ffa_lend_reclaimed(struct device *dev, struct page *page, u64 nr_pages) +{ + if (!ffa_lend_pool_can_set_direct_map(dev, page, nr_pages)) + return; + + __set_direct_map_default_noflush(page, nr_pages); + + atomic_dec_return_release(&ffa_lend_pool_active); +} +EXPORT_SYMBOL_GPL(ffa_lend_reclaimed); + +static int ffa_lend_pool_pm_notify(struct notifier_block *nb, unsigned long mode, void *data) +{ + /* Prevent hibernation which would try to access lent memory */ + switch (mode) { + case PM_HIBERNATION_PREPARE: + if (atomic_cmpxchg_acquire(&ffa_lend_pool_active, 0, FFA_LEND_POOL_DISABLED)) + return notifier_from_errno(-EBUSY); + break; + case PM_POST_HIBERNATION: + atomic_set(&ffa_lend_pool_active, 0); + } + + return NOTIFY_DONE; +} + +static struct notifier_block ffa_lend_pool_pm_nb = { + .notifier_call = ffa_lend_pool_pm_notify, +}; + +static const struct reserved_mem_ops ffa_lend_pool_ops; + +static struct reserved_mem *ffa_lend_pool_get_rmem(void) +{ + struct reserved_mem *rmem; + struct device_node *np; + + np = of_find_compatible_node(NULL, NULL, "arm,ffa-lend-pool"); + if (!np) + return NULL; + + rmem = of_reserved_mem_lookup(np); + of_node_put(np); + + if (WARN_ON_ONCE(rmem && rmem->ops != &ffa_lend_pool_ops)) + return NULL; + + return rmem; +} + +/** + * ffa_lend_pool_attach() - Attach a device to the FF-A lend pool + * @dev: Device to attach + * + * FF-A devices are dynamically discovered and might not have an associated + * device tree node with a "memory-region" phandle. In that case, drivers must + * use this function to attach to the "arm,ffa-lend-pool" reserved memory + * region. + * + * Return: 0 on success, negative error code otherwise. + */ +int ffa_lend_pool_attach(struct device *dev) +{ + struct reserved_mem *rmem = ffa_lend_pool_get_rmem(); + + return rmem ? rmem->ops->device_init(rmem, dev) : -ENODEV; +} +EXPORT_SYMBOL_GPL(ffa_lend_pool_attach); + +/** + * ffa_lend_pool_detach() - Detach a device from the FF-A lend pool + * @dev: Device to detach + * + * Releases the device from the "arm,ffa-lend-pool" reserved memory region. + */ +void ffa_lend_pool_detach(struct device *dev) +{ + struct reserved_mem *rmem = ffa_lend_pool_get_rmem(); + + if (rmem) + rmem->ops->device_release(rmem, dev); +} +EXPORT_SYMBOL_GPL(ffa_lend_pool_detach); + +static int __init ffa_lend_pool_setup(unsigned long node, struct reserved_mem *rmem) +{ + struct cma *cma; + int ret; + + /* Limited by ffa_lend_pool_active */ + if (rmem->size / PAGE_SIZE > INT_MAX) + return -E2BIG; + + if (!IS_ALIGNED(rmem->base | rmem->size, CMA_MIN_ALIGNMENT_BYTES)) { + pr_err("FF-A lend pool: incorrect alignment of CMA region\n"); + return -EINVAL; + } + + ret = memblock_mark_ptemap(rmem->base, rmem->size); + if (ret) + return ret; + + ret = cma_init_reserved_mem(rmem->base, rmem->size, 0, rmem->name, &cma); + if (ret) { + pr_err("FF-A lend pool: unable to setup CMA region (%d)\n", ret); + memblock_clear_ptemap(rmem->base, rmem->size); + return ret; + } + + register_pm_notifier(&ffa_lend_pool_pm_nb); + rmem->priv = cma; + + return 0; +} + +static int ffa_lend_pool_device_init(struct reserved_mem *rmem, struct device *dev) +{ + int ret; + + if (!can_set_direct_map_range(pfn_to_page(PHYS_PFN(rmem->base)), rmem->size / PAGE_SIZE)) { + pr_err("FF-A lend pool: reserved memory cannot be unmapped in direct map\n"); + return -EINVAL; + } + + dev->cma_area = rmem->priv; + + ret = xa_err(xa_store(&ffa_lend_pool_devices, (unsigned long)dev, dev, GFP_KERNEL)); + if (ret) + dev->cma_area = NULL; + + return ret; +} + +static void ffa_lend_pool_device_release(struct reserved_mem *rmem, struct device *dev) +{ + xa_erase(&ffa_lend_pool_devices, (unsigned long)dev); + dev->cma_area = NULL; +} + +static const struct reserved_mem_ops ffa_lend_pool_ops = { + .node_init = ffa_lend_pool_setup, + .device_init = ffa_lend_pool_device_init, + .device_release = ffa_lend_pool_device_release, +}; +RESERVEDMEM_OF_DECLARE(ffa_lend_pool, "arm,ffa-lend-pool", &ffa_lend_pool_ops); diff --git a/include/linux/arm_ffa.h b/include/linux/arm_ffa.h index e71d83ee0aef..8608847931cc 100644 --- a/include/linux/arm_ffa.h +++ b/include/linux/arm_ffa.h @@ -519,4 +519,27 @@ struct ffa_ops { const struct ffa_notifier_ops *notifier_ops; };
+struct page; + +#if IS_ENABLED(CONFIG_ARM_FFA_LEND_POOL) +int ffa_lend_pool_attach(struct device *dev); +void ffa_lend_pool_detach(struct device *dev); +int ffa_prepare_lend(struct device *dev, struct page *page, u64 nr_pages); +void ffa_lend_reclaimed(struct device *dev, struct page *page, u64 nr_pages); +#else +static inline int ffa_lend_pool_attach(struct device *dev) +{ + return -ENODEV; +} +static inline void ffa_lend_pool_detach(struct device *dev) +{ +} +static inline int ffa_prepare_lend(struct device *dev, struct page *page, u64 nr_pages) +{ + return -ENODEV; +} +static inline void ffa_lend_reclaimed(struct device *dev, struct page *page, u64 nr_pages) +{ +} +#endif #endif /* _LINUX_ARM_FFA_H */