drivers/misc/sram-exec.c

   1 /*
   2  * SRAM protect-exec region helper functions
   3  *
   4  * Copyright (C) 2017 Texas Instruments Incorporated - http://www.ti.com/
   5  *      Dave Gerlach
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  *
  11  * This program is distributed "as is" WITHOUT ANY WARRANTY of any
  12  * kind, whether express or implied; without even the implied warranty
  13  * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  */
  16
  17 #include <linux/device.h>
  18 #include <linux/genalloc.h>
  19 #include <linux/mm.h>
  20 #include <linux/sram.h>
  21
  22 #include <asm/fncpy.h>
  23 #include <asm/set_memory.h>
  24
  25 #include "sram.h"
  26
  27 static DEFINE_MUTEX(exec_pool_list_mutex);
  28 static LIST_HEAD(exec_pool_list);
  29
  30 int sram_check_protect_exec(struct sram_dev *sram, struct sram_reserve *block,
  31                             struct sram_partition *part)
  32 {
  33         unsigned long base = (unsigned long)part->base;
  34         unsigned long end = base + block->size;
  35
  36         if (!PAGE_ALIGNED(base) || !PAGE_ALIGNED(end)) {
  37                 dev_err(sram->dev,
  38                         "SRAM pool marked with 'protect-exec' is not page aligned and will not be created.\n");
  39                 return -ENOMEM;
  40         }
  41
  42         return 0;
  43 }
  44
  45 int sram_add_protect_exec(struct sram_partition *part)
  46 {
  47         mutex_lock(&exec_pool_list_mutex);
  48         list_add_tail(&part->list, &exec_pool_list);
  49         mutex_unlock(&exec_pool_list_mutex);
  50
  51         return 0;
  52 }
  53
  54 /**
  55  * sram_exec_copy - copy data to a protected executable region of sram
  56  *
  57  * @pool: struct gen_pool retrieved that is part of this sram
  58  * @dst: Destination address for the copy, that must be inside pool
  59  * @src: Source address for the data to copy
  60  * @size: Size of copy to perform, which starting from dst, must reside in pool
  61  *
  62  * Return: Address for copied data that can safely be called through function
  63  *         pointer, or NULL if problem.
  64  *
  65  * This helper function allows sram driver to act as central control location
  66  * of 'protect-exec' pools which are normal sram pools but are always set
  67  * read-only and executable except when copying data to them, at which point
  68  * they are set to read-write non-executable, to make sure no memory is
  69  * writeable and executable at the same time. This region must be page-aligned
  70  * and is checked during probe, otherwise page attribute manipulation would
  71  * not be possible. Care must be taken to only call the returned address as
  72  * dst address is not guaranteed to be safely callable.
  73  *
  74  * NOTE: This function uses the fncpy macro to move code to the executable
  75  * region. Some architectures have strict requirements for relocating
  76  * executable code, so fncpy is a macro that must be defined by any arch
  77  * making use of this functionality that guarantees a safe copy of exec
  78  * data and returns a safe address that can be called as a C function
  79  * pointer.
  80  */
  81 void *sram_exec_copy(struct gen_pool *pool, void *dst, void *src,
  82                      size_t size)
  83 {
  84         struct sram_partition *part = NULL, *p;
  85         unsigned long base;
  86         int pages;
  87         void *dst_cpy;
  88         int ret;
  89
  90         mutex_lock(&exec_pool_list_mutex);
  91         list_for_each_entry(p, &exec_pool_list, list) {
  92                 if (p->pool == pool)
  93                         part = p;
  94         }
  95         mutex_unlock(&exec_pool_list_mutex);
  96
  97         if (!part)
  98                 return NULL;
  99
 100         if (!gen_pool_has_addr(pool, (unsigned long)dst, size))
 101                 return NULL;
 102
 103         base = (unsigned long)part->base;
 104         pages = PAGE_ALIGN(size) / PAGE_SIZE;
 105
 106         mutex_lock(&part->lock);
 107
 108         ret = set_memory_nx((unsigned long)base, pages);
 109         if (ret)
 110                 goto error_out;
 111         ret = set_memory_rw((unsigned long)base, pages);
 112         if (ret)
 113                 goto error_out;
 114
 115         dst_cpy = fncpy(dst, src, size);
 116
 117         ret = set_memory_ro((unsigned long)base, pages);
 118         if (ret)
 119                 goto error_out;
 120         ret = set_memory_x((unsigned long)base, pages);
 121         if (ret)
 122                 goto error_out;
 123
 124         mutex_unlock(&part->lock);
 125
 126         return dst_cpy;
 127
 128 error_out:
 129         mutex_unlock(&part->lock);
 130         return NULL;
 131 }
 132 EXPORT_SYMBOL_GPL(sram_exec_copy);