[PATCH v2 7/8] execmem: add support for cache of large ROX pages

Mike Rapoport
2024-08-26T06:59:36Z

Using large pages to map text areas reduces iTLB pressure and improves
performance.

Extend execmem_alloc() with an ability to use PMD_SIZE'ed pages with ROX
permissions as a cache for smaller allocations.

To populate the cache, a writable large page is allocated from vmalloc with
VM_ALLOW_HUGE_VMAP, filled with invalid instructions and then remapped as
ROX.

Portions of that large page are handed out to execmem_alloc() callers
without any changes to the permissions.

When the memory is freed with execmem_free() it is invalidated again so
that it won't contain stale instructions.

The cache is enabled when an architecture sets EXECMEM_ROX_CACHE flag in
definition of an execmem_range.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
include/linux/execmem.h | 2 +
mm/execmem.c | 290 +++++++++++++++++++++++++++++++++++++++-
2 files changed, 287 insertions(+), 5 deletions(-)

diff --git a/include/linux/execmem.h b/include/linux/execmem.h
index dfdf19f8a5e8..7436aa547818 100644
--- a/include/linux/execmem.h
+++ b/include/linux/execmem.h
@@ -77,12 +77,14 @@ struct execmem_range {

/**
* struct execmem_info - architecture parameters for code allocations
+ * @fill_trapping_insns: set memory to contain instructions that will trap
* @ranges: array of parameter sets defining architecture specific
* parameters for executable memory allocations. The ranges that are not
* explicitly initialized by an architecture use parameters defined for
* @EXECMEM_DEFAULT.
*/
struct execmem_info {
+ void (*fill_trapping_insns)(void *ptr, size_t size, bool writable);
struct execmem_range ranges[EXECMEM_TYPE_MAX];
};

diff --git a/mm/execmem.c b/mm/execmem.c
index 0f6691e9ffe6..3bde0863c50a 100644
--- a/mm/execmem.c
+++ b/mm/execmem.c
@@ -7,28 +7,88 @@
*/

#include <linux/mm.h>
+#include <linux/mutex.h>
#include <linux/vmalloc.h>
#include <linux/execmem.h>
+#include <linux/maple_tree.h>
#include <linux/moduleloader.h>
#include <linux/text-patching.h>

+#include <asm/tlbflush.h>
+
+#include "internal.h"
+
static struct execmem_info *execmem_info __ro_after_init;
static struct execmem_info default_execmem_info __ro_after_init;

-static void *__execmem_alloc(struct execmem_range *range, size_t size)
+#ifdef CONFIG_MMU
+struct execmem_cache {
+ struct mutex mutex;
+ struct maple_tree busy_areas;
+ struct maple_tree free_areas;
+};
+
+static struct execmem_cache execmem_cache = {
+ .mutex = __MUTEX_INITIALIZER(execmem_cache.mutex),
+ .busy_areas = MTREE_INIT_EXT(busy_areas, MT_FLAGS_LOCK_EXTERN,
+ execmem_cache.mutex),
+ .free_areas = MTREE_INIT_EXT(free_areas, MT_FLAGS_LOCK_EXTERN,
+ execmem_cache.mutex),
+};
+
+static void execmem_cache_clean(struct work_struct *work)
+{
+ struct maple_tree *free_areas = &execmem_cache.free_areas;
+ struct mutex *mutex = &execmem_cache.mutex;
+ MA_STATE(mas, free_areas, 0, ULONG_MAX);
+ void *area;
+
+ mutex_lock(mutex);
+ mas_for_each(&mas, area, ULONG_MAX) {
+ size_t size;
+
+ if (!xa_is_value(area))
+ continue;
+
+ size = xa_to_value(area);
+
+ if (IS_ALIGNED(size, PMD_SIZE) &&
+ IS_ALIGNED(mas.index, PMD_SIZE)) {
+ void *ptr = (void *)mas.index;
+
+ mas_erase(&mas);
+ vfree(ptr);
+ }
+ }
+ mutex_unlock(mutex);
+}
+
+static DECLARE_WORK(execmem_cache_clean_work, execmem_cache_clean);
+
+static void execmem_fill_trapping_insns(void *ptr, size_t size, bool writable)
+{
+ if (execmem_info->fill_trapping_insns)
+ execmem_info->fill_trapping_insns(ptr, size, writable);
+ else
+ memset(ptr, 0, size);
+}
+
+static void *execmem_vmalloc(struct execmem_range *range, size_t size,
+ pgprot_t pgprot, unsigned long vm_flags)
{
bool kasan = range->flags & EXECMEM_KASAN_SHADOW;
- unsigned long vm_flags = VM_FLUSH_RESET_PERMS;
gfp_t gfp_flags = GFP_KERNEL | __GFP_NOWARN;
+ unsigned int align = range->alignment;
unsigned long start = range->start;
unsigned long end = range->end;
- unsigned int align = range->alignment;
- pgprot_t pgprot = range->pgprot;
void *p;

if (kasan)
vm_flags |= VM_DEFER_KMEMLEAK;

+ if (vm_flags & VM_ALLOW_HUGE_VMAP)
+ align = PMD_SIZE;
+
p = __vmalloc_node_range(size, align, start, end, gfp_flags,
pgprot, vm_flags, NUMA_NO_NODE,
__builtin_return_address(0));
@@ -50,8 +110,226 @@ static void *__execmem_alloc(struct execmem_range *range, size_t size)
return NULL;
}

+ return p;
+}
+
+static int execmem_cache_add(void *ptr, size_t size)
+{
+ struct maple_tree *free_areas = &execmem_cache.free_areas;
+ struct mutex *mutex = &execmem_cache.mutex;
+ unsigned long addr = (unsigned long)ptr;
+ MA_STATE(mas, free_areas, addr - 1, addr + 1);
+ unsigned long lower, lower_size = 0;
+ unsigned long upper, upper_size = 0;
+ unsigned long area_size;
+ void *area = NULL;
+ int err;
+
+ lower = addr;
+ upper = addr + size - 1;
+
+ mutex_lock(mutex);
+ area = mas_walk(&mas);
+ if (area && xa_is_value(area) && mas.last == addr - 1) {
+ lower = mas.index;
+ lower_size = xa_to_value(area);
+ }
+
+ area = mas_next(&mas, ULONG_MAX);
+ if (area && xa_is_value(area) && mas.index == addr + size) {
+ upper = mas.last;
+ upper_size = xa_to_value(area);
+ }
+
+ mas_set_range(&mas, lower, upper);
+ area_size = lower_size + upper_size + size;
+ err = mas_store_gfp(&mas, xa_mk_value(area_size), GFP_KERNEL);
+ mutex_unlock(mutex);
+ if (err)
+ return -ENOMEM;
+
+ return 0;
+}
+
+static bool within_range(struct execmem_range *range, struct ma_state *mas,
+ size_t size)
+{
+ unsigned long addr = mas->index;
+
+ if (addr >= range->start && addr + size < range->end)
+ return true;
+
+ if (range->fallback_start &&
+ addr >= range->fallback_start && addr + size < range->fallback_end)
+ return true;
+
+ return false;
+}
+
+static void *__execmem_cache_alloc(struct execmem_range *range, size_t size)
+{
+ struct maple_tree *free_areas = &execmem_cache.free_areas;
+ struct maple_tree *busy_areas = &execmem_cache.busy_areas;
+ MA_STATE(mas_free, free_areas, 0, ULONG_MAX);
+ MA_STATE(mas_busy, busy_areas, 0, ULONG_MAX);
+ struct mutex *mutex = &execmem_cache.mutex;
+ unsigned long addr, last, area_size = 0;
+ void *area, *ptr = NULL;
+ int err;
+
+ mutex_lock(mutex);
+ mas_for_each(&mas_free, area, ULONG_MAX) {
+ area_size = xa_to_value(area);
+
+ if (area_size >= size && within_range(range, &mas_free, size))
+ break;
+ }
+
+ if (area_size < size)
+ goto out_unlock;
+
+ addr = mas_free.index;
+ last = mas_free.last;
+
+ /* insert allocated size to busy_areas at range [addr, addr + size) */
+ mas_set_range(&mas_busy, addr, addr + size - 1);
+ err = mas_store_gfp(&mas_busy, xa_mk_value(size), GFP_KERNEL);
+ if (err)
+ goto out_unlock;
+
+ mas_erase(&mas_free);
+ if (area_size > size) {
+ /*
+ * re-insert remaining free size to free_areas at range
+ * [addr + size, last]
+ */
+ mas_set_range(&mas_free, addr + size, last);
+ size = area_size - size;
+ err = mas_store_gfp(&mas_free, xa_mk_value(size), GFP_KERNEL);
+ if (err) {
+ mas_erase(&mas_busy);
+ goto out_unlock;
+ }
+ }
+ ptr = (void *)addr;
+
+out_unlock:
+ mutex_unlock(mutex);
+ return ptr;
+}
+
+static int execmem_cache_populate(struct execmem_range *range, size_t size)
+{
+ unsigned long vm_flags = VM_FLUSH_RESET_PERMS | VM_ALLOW_HUGE_VMAP;
+ unsigned long start, end;
+ struct vm_struct *vm;
+ size_t alloc_size;
+ int err = -ENOMEM;
+ void *p;
+
+ alloc_size = round_up(size, PMD_SIZE);
+ p = execmem_vmalloc(range, alloc_size, PAGE_KERNEL, vm_flags);
+ if (!p)
+ return err;
+
+ vm = find_vm_area(p);
+ if (!vm)
+ goto err_free_mem;
+
+ /* fill memory with instructions that will trap */
+ execmem_fill_trapping_insns(p, alloc_size, /* writable = */ true);
+
+ start = (unsigned long)p;
+ end = start + alloc_size;
+
+ vunmap_range_noflush(start, end);
+ flush_tlb_kernel_range(start, end);
+
+ err = vmap_pages_range_noflush(start, end, range->pgprot, vm->pages,
+ PMD_SHIFT);
+ if (err)
+ goto err_free_mem;
+
+ err = execmem_cache_add(p, alloc_size);
+ if (err)
+ goto err_free_mem;
+
+ return 0;
+
+err_free_mem:
+ vfree(p);
+ return err;
+}
+
+static void *execmem_cache_alloc(struct execmem_range *range, size_t size)
+{
+ void *p;
+ int err;
+
+ p = __execmem_cache_alloc(range, size);
+ if (p)
+ return p;
+
+ err = execmem_cache_populate(range, size);
+ if (err)
+ return NULL;
+
+ return __execmem_cache_alloc(range, size);
+}
+
+static bool execmem_cache_free(void *ptr)
+{
+ struct maple_tree *busy_areas = &execmem_cache.busy_areas;
+ struct mutex *mutex = &execmem_cache.mutex;
+ unsigned long addr = (unsigned long)ptr;
+ MA_STATE(mas, busy_areas, addr, addr);
+ size_t size;
+ void *area;
+
+ mutex_lock(mutex);
+ area = mas_walk(&mas);
+ if (!area) {
+ mutex_unlock(mutex);
+ return false;
+ }
+ size = xa_to_value(area);
+ mas_erase(&mas);
+ mutex_unlock(mutex);
+
+ execmem_fill_trapping_insns(ptr, size, /* writable = */ false);
+
+ execmem_cache_add(ptr, size);
+
+ schedule_work(&execmem_cache_clean_work);
+
+ return true;
+}
+
+static void *__execmem_alloc(struct execmem_range *range, size_t size)
+{
+ bool use_cache = range->flags & EXECMEM_ROX_CACHE;
+ unsigned long vm_flags = VM_FLUSH_RESET_PERMS;
+ pgprot_t pgprot = range->pgprot;
+ void *p;
+
+ if (use_cache)
+ p = execmem_cache_alloc(range, size);
+ else
+ p = execmem_vmalloc(range, size, pgprot, vm_flags);
+
return kasan_reset_tag(p);
}
+#else
+static void *__execmem_alloc(struct execmem_range *range, size_t size)
+{
+ return vmalloc(size);
+}
+
+static bool execmem_cache_free(void *ptr)
+{
+ return false;
+}
+#endif

void *execmem_alloc(enum execmem_type type, size_t size)
{
@@ -67,7 +345,9 @@ void execmem_free(void *ptr)
* supported by vmalloc.
*/
WARN_ON(in_interrupt());
- vfree(ptr);
+
+ if (!execmem_cache_free(ptr))
+ vfree(ptr);
}

void *execmem_update_copy(void *dst, const void *src, size_t size)
--
2.43.0