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mm: Adjust new region size to take management overhead into account

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When grub_memalign() encounters out-of-memory, it will try
grub_mm_add_region_fn() to request more memory from system firmware.
However, the size passed to it doesn't take region management overhead
into account. Adding a memory area of "size" bytes may result in a heap
region of less than "size" bytes really available. Thus, the new region
may not be adequate for current allocation request, confusing
out-of-memory handling code.

This patch introduces GRUB_MM_MGMT_OVERHEAD to address the region
management overhead (e.g. metadata, padding). The value of this new
constant must be large enough to make sure grub_memalign(align, size)
always succeeds after a successful call to
  grub_mm_init_region(addr, size + align + GRUB_MM_MGMT_OVERHEAD),
for any given addr and size (assuming no integer overflow).

The size passed to grub_mm_add_region_fn() is now correctly adjusted,
thus if grub_mm_add_region_fn() succeeded, current allocation request
can always succeed.

Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Zhang Boyang 2023-01-29 19:49:31 +08:00 committed by Daniel Kiper
parent 6d729ced70
commit 2282cbfe5a
1 changed files with 61 additions and 3 deletions
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64
grub-core/kern/mm.c
View File

@ -83,6 +83,46 @@
/*
* GRUB_MM_MGMT_OVERHEAD is an upper bound of management overhead of
* each region, with any possible padding taken into account.
*
* The value must be large enough to make sure grub_memalign(align, size)
* always succeeds after a successful call to
* grub_mm_init_region(addr, size + align + GRUB_MM_MGMT_OVERHEAD),
* for any given addr, align and size (assuming no interger overflow).
*
* The worst case which has maximum overhead is shown in the figure below:
*
* +-- addr
* v |<- size + align ->|
* +---------+----------------+----------------+------------------+---------+
* | padding | grub_mm_region | grub_mm_header | usable bytes | padding |
* +---------+----------------+----------------+------------------+---------+
* |<- a ->|<- b ->|<- c ->|<- d ->|<- e ->|
* ^
* b == sizeof (struct grub_mm_region) | / Assuming no other suitable
* c == sizeof (struct grub_mm_header) | | block is available, then:
* d == size + align +-| If align == 0, this will be
* | the pointer returned by next
* Assuming addr % GRUB_MM_ALIGN == 1, then: | grub_memalign(align, size).
* a == GRUB_MM_ALIGN - 1 | If align > 0, this chunk may
* | need to be split to fulfill
* Assuming d % GRUB_MM_ALIGN == 1, then: | alignment requirements, and
* e == GRUB_MM_ALIGN - 1 | the returned pointer may be
* \ inside these usable bytes.
* Therefore, the maximum overhead is:
* a + b + c + e == (GRUB_MM_ALIGN - 1) + sizeof (struct grub_mm_region)
* + sizeof (struct grub_mm_header) + (GRUB_MM_ALIGN - 1)
*/
#define GRUB_MM_MGMT_OVERHEAD ((GRUB_MM_ALIGN - 1) \
+ sizeof (struct grub_mm_region) \
+ sizeof (struct grub_mm_header) \
+ (GRUB_MM_ALIGN - 1))
/* The size passed to grub_mm_add_region_fn() is aligned up by this value. */
#define GRUB_MM_HEAP_GROW_ALIGN 4096
grub_mm_region_t grub_mm_base;
grub_mm_add_region_func_t grub_mm_add_region_fn;
@ -230,6 +270,11 @@ grub_mm_init_region (void *addr, grub_size_t size)
grub_dprintf ("regions", "No: considering a new region at %p of size %" PRIxGRUB_SIZE "\n",
addr, size);
/*
* If you want to modify the code below, please also take a look at
* GRUB_MM_MGMT_OVERHEAD and make sure it is synchronized with the code.
*/
/* Allocate a region from the head. */
r = (grub_mm_region_t) ALIGN_UP ((grub_addr_t) addr, GRUB_MM_ALIGN);
@ -410,6 +455,7 @@ grub_memalign (grub_size_t align, grub_size_t size)
{
grub_mm_region_t r;
grub_size_t n = ((size + GRUB_MM_ALIGN - 1) >> GRUB_MM_ALIGN_LOG2) + 1;
grub_size_t grow;
int count = 0;
if (!grub_mm_base)
@ -418,10 +464,22 @@ grub_memalign (grub_size_t align, grub_size_t size)
if (size > ~(grub_size_t) align)
goto fail;
/*
* Pre-calculate the necessary size of heap growth (if applicable),
* with region management overhead taken into account.
*/
if (grub_add (size + align, GRUB_MM_MGMT_OVERHEAD, &grow))
goto fail;
/* Align up heap growth to make it friendly to CPU/MMU. */
if (grow > ~(grub_size_t) (GRUB_MM_HEAP_GROW_ALIGN - 1))
goto fail;
grow = ALIGN_UP (grow, GRUB_MM_HEAP_GROW_ALIGN);
/* We currently assume at least a 32-bit grub_size_t,
so limiting allocations to <adress space size> - 1MiB
in name of sanity is beneficial. */
if ((size + align) > ~(grub_size_t) 0x100000)
if (grow > ~(grub_size_t) 0x100000)
goto fail;
align = (align >> GRUB_MM_ALIGN_LOG2);
@ -447,7 +505,7 @@ grub_memalign (grub_size_t align, grub_size_t size)
count++;
if (grub_mm_add_region_fn != NULL &&
grub_mm_add_region_fn (size, GRUB_MM_ADD_REGION_CONSECUTIVE) == GRUB_ERR_NONE)
grub_mm_add_region_fn (grow, GRUB_MM_ADD_REGION_CONSECUTIVE) == GRUB_ERR_NONE)
goto again;
/* fallthrough */
@ -462,7 +520,7 @@ grub_memalign (grub_size_t align, grub_size_t size)
* Try again even if this fails, in case it was able to partially
* satisfy the request
*/
grub_mm_add_region_fn (size, GRUB_MM_ADD_REGION_NONE);
grub_mm_add_region_fn (grow, GRUB_MM_ADD_REGION_NONE);
goto again;
}