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Ensure addresses in is_mem_free() don't overflow 

This patch adds some runtime checks to prevent some potential
pointer overflow issues in the is_mem_free() function. The overflow
could happen in the case where the end addresses, computed as the
sum of a base address and a size, results in a value large enough
to wrap around. This, in turn, could lead to unpredictable behaviour.

If such an overflow is detected, the is_mem_free() function will now
declare the memory region as not free. The overflow is detected using
a new macro, called check_uptr_overflow().

This patch also modifies all other places in the 'bl_common.c' file
where an end address was computed as the sum of a base address and a
size and instead keeps the two values separate. This avoids the need
to handle pointer overflows everywhere. The code doesn't actually need
to compute any end address before the is_mem_free() function is called
other than to print information message to the serial output.

This patch also introduces 2 slight changes to the reserve_mem()
function:

 - It fixes the end addresses passed to choose_mem_pos(). It was
   incorrectly passing (base + size) instead of (base + size - 1).

 - When the requested allocation size is 0, the function now exits
   straight away and says so using a warning message.
   Previously, it used to actually reserve some memory. A zero-byte
   allocation was not considered as a special case so the function
   was using the same top/bottom allocation mechanism as for any
   other allocation. As a result, the smallest area of memory starting
   from the requested base address within the free region was
   reserved.

Change-Id: I0e695f961e24e56ffe000718014e0496dc6e1ec6
This commit is contained in:
Sandrine Bailleux 2016-07-12 09:12:24 +01:00
parent 3a26a28c72
commit 7b6d330c92
2 changed files with 61 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

69
common/bl_common.c
View File

@ -38,6 +38,7 @@
#include <io_storage.h>
#include <platform.h>
#include <string.h>
#include <utils.h>
#include <xlat_tables.h>
uintptr_t page_align(uintptr_t value, unsigned dir)
@ -59,12 +60,44 @@ static inline unsigned int is_page_aligned (uintptr_t addr) {
/******************************************************************************
* Determine whether the memory region delimited by 'addr' and 'size' is free,
* given the extents of free memory.
* Return 1 if it is free, 0 otherwise.
* Return 1 if it is free, 0 if it is not free or if the input values are
* invalid.
*****************************************************************************/
static int is_mem_free(uintptr_t free_base, size_t free_size,
uintptr_t addr, size_t size)
{
return (addr >= free_base) && (addr + size <= free_base + free_size);
uintptr_t free_end, requested_end;
/*
* Handle corner cases first.
*
* The order of the 2 tests is important, because if there's no space
* left (i.e. free_size == 0) but we don't ask for any memory
* (i.e. size == 0) then we should report that the memory is free.
*/
if (size == 0)
return 1; /* A zero-byte region is always free */
if (free_size == 0)
return 0;
/*
* Check that the end addresses don't overflow.
* If they do, consider that this memory region is not free, as this
* is an invalid scenario.
*/
if (check_uptr_overflow(free_base, free_size - 1))
return 0;
free_end = free_base + (free_size - 1);
if (check_uptr_overflow(addr, size - 1))
return 0;
requested_end = addr + (size - 1);
/*
* Finally, check that the requested memory region lies within the free
* region.
*/
return (addr >= free_base) && (requested_end <= free_end);
}
/******************************************************************************
@ -100,7 +133,8 @@ static unsigned int choose_mem_pos(uintptr_t mem_start, uintptr_t mem_end,
* Reserve the memory region delimited by 'addr' and 'size'. The extents of free
* memory are passed in 'free_base' and 'free_size' and they will be updated to
* reflect the memory usage.
* The caller must ensure the memory to reserve is free.
* The caller must ensure the memory to reserve is free and that the addresses
* and sizes passed in arguments are sane.
*****************************************************************************/
void reserve_mem(uintptr_t *free_base, size_t *free_size,
uintptr_t addr, size_t size)
@ -113,8 +147,13 @@ void reserve_mem(uintptr_t *free_base, size_t *free_size,
assert(free_size != NULL);
assert(is_mem_free(*free_base, *free_size, addr, size));
pos = choose_mem_pos(*free_base, *free_base + *free_size,
addr, addr + size,
if (size == 0) {
WARN("Nothing to allocate, requested size is zero\n");
return;
}
pos = choose_mem_pos(*free_base, *free_base + (*free_size - 1),
addr, addr + (size - 1),
&discard_size);
reserved_size = size + discard_size;
@ -135,10 +174,10 @@ static void dump_load_info(uintptr_t image_load_addr,
INFO("Trying to load image at address %p, size = 0x%zx\n",
(void *)image_load_addr, image_size);
INFO("Current memory layout:\n");
INFO(" total region = [%p, %p]\n", (void *)mem_layout->total_base,
(void *)(mem_layout->total_base + mem_layout->total_size));
INFO(" free region = [%p, %p]\n", (void *)mem_layout->free_base,
(void *)(mem_layout->free_base + mem_layout->free_size));
INFO(" total region = [base = %p, size = 0x%zx]\n",
(void *) mem_layout->total_base, mem_layout->total_size);
INFO(" free region = [base = %p, size = 0x%zx]\n",
(void *) mem_layout->free_base, mem_layout->free_size);
}
/* Generic function to return the size of an image */
@ -248,8 +287,8 @@ int load_image(meminfo_t *mem_layout,
/* Check that the memory where the image will be loaded is free */
if (!is_mem_free(mem_layout->free_base, mem_layout->free_size,
image_base, image_size)) {
WARN("Failed to reserve memory: %p - %p\n", (void *) image_base,
(void *) (image_base + image_size));
WARN("Failed to reserve region [base = %p, size = 0x%zx]\n",
(void *) image_base, image_size);
dump_load_info(image_base, image_size, mem_layout);
io_result = -ENOMEM;
goto exit;
@ -278,8 +317,8 @@ int load_image(meminfo_t *mem_layout,
image_base, image_size);
entry_point_info->pc = image_base;
} else {
INFO("Skip reserving memory: %p - %p\n", (void *) image_base,
(void *) (image_base + image_size));
INFO("Skip reserving region [base = %p, size = 0x%zx]\n",
(void *) image_base, image_size);
}
/*
@ -289,8 +328,8 @@ int load_image(meminfo_t *mem_layout,
*/
flush_dcache_range(image_base, image_size);
INFO("Image id=%u loaded: %p - %p\n", image_id, (void *) image_base,
(void *) (image_base + image_size));
INFO("Image id=%u loaded at address %p, size = 0x%zx\n", image_id,
(void *) image_base, image_size);
exit:
io_close(image_handle);

7
include/lib/utils.h
View File

@ -55,4 +55,11 @@
#define round_down(value, boundary) \
((value) & ~round_boundary(value, boundary))
/*
* Evaluates to 1 if (ptr + inc) overflows, 0 otherwise.
* Both arguments must be unsigned pointer values (i.e. uintptr_t).
*/
#define check_uptr_overflow(ptr, inc) \
(((ptr) > UINTPTR_MAX - (inc)) ? 1 : 0)
#endif /* __UTILS_H__ */