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Commit d0b4d64a authored by Matt Wilson's avatar Matt Wilson Committed by Konrad Rzeszutek Wilk
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xen/grant-table: correctly initialize grant table version 1 



Commit 85ff6acb (xen/granttable: Grant
tables V2 implementation) changed the GREFS_PER_GRANT_FRAME macro from
a constant to a conditional expression. The expression depends on
grant_table_version being appropriately set. Unfortunately, at init
time grant_table_version will be 0. The GREFS_PER_GRANT_FRAME
conditional expression checks for "grant_table_version == 1", and
therefore returns the number of grant references per frame for v2.

This causes gnttab_init() to allocate fewer pages for gnttab_list, as
a frame can old half the number of v2 entries than v1 entries. After
gnttab_resume() is called, grant_table_version is appropriately
set. nr_init_grefs will then be miscalculated and gnttab_free_count
will hold a value larger than the actual number of free gref entries.

If a guest is heavily utilizing improperly initialized v1 grant
tables, memory corruption can occur. One common manifestation is
corruption of the vmalloc list, resulting in a poisoned pointer
derefrence when accessing /proc/meminfo or /proc/vmallocinfo:

[   40.770064] BUG: unable to handle kernel paging request at 0000200200001407
[   40.770083] IP: [<ffffffff811a6fb0>] get_vmalloc_info+0x70/0x110
[   40.770102] PGD 0
[   40.770107] Oops: 0000 [#1] SMP
[   40.770114] CPU 10

This patch introduces a static variable, grefs_per_grant_frame, to
cache the calculated value. gnttab_init() now calls
gnttab_request_version() early so that grant_table_version and
grefs_per_grant_frame can be appropriately set. A few BUG_ON()s have
been added to prevent this type of bug from reoccurring in the future.

Signed-off-by: default avatarMatt Wilson <msw@amazon.com>
Reviewed-and-Tested-by: default avatarSteven Noonan <snoonan@amazon.com>
Acked-by: default avatarIan Campbell <Ian.Campbell@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Annie Li <annie.li@oracle.com>
Cc: xen-devel@lists.xen.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org # v3.3 and newer
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent 6337a239

drivers/xen/grant-table.c

+29 −19
Original line number Diff line number Diff line
@@ -56,10 +56,6 @@ 
/* External tools reserve first few grant table entries. */

#define NR_RESERVED_ENTRIES 8

#define GNTTAB_LIST_END 0xffffffff

#define GREFS_PER_GRANT_FRAME \

(grant_table_version == 1 ?                      \

(PAGE_SIZE / sizeof(struct grant_entry_v1)) :   \

(PAGE_SIZE / sizeof(union grant_entry_v2)))



static grant_ref_t **gnttab_list;

static unsigned int nr_grant_frames;
@@ -154,6 +150,7 @@ static struct gnttab_ops *gnttab_interface; 
static grant_status_t *grstatus;



static int grant_table_version;

static int grefs_per_grant_frame;



static struct gnttab_free_callback *gnttab_free_callback_list;
@@ -767,12 +764,14 @@ static int grow_gnttab_list(unsigned int more_frames) 
	unsigned int new_nr_grant_frames, extra_entries, i;

	unsigned int nr_glist_frames, new_nr_glist_frames;



	BUG_ON(grefs_per_grant_frame == 0);



	new_nr_grant_frames = nr_grant_frames + more_frames;

	extra_entries       = more_frames * GREFS_PER_GRANT_FRAME;

	extra_entries       = more_frames * grefs_per_grant_frame;



	nr_glist_frames = (nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;

	nr_glist_frames = (nr_grant_frames * grefs_per_grant_frame + RPP - 1) / RPP;

	new_nr_glist_frames =

		(new_nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;

		(new_nr_grant_frames * grefs_per_grant_frame + RPP - 1) / RPP;

	for (i = nr_glist_frames; i < new_nr_glist_frames; i++) {

		gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_ATOMIC);

		if (!gnttab_list[i])
@@ -780,12 +779,12 @@ static int grow_gnttab_list(unsigned int more_frames) 
	}





	for (i = GREFS_PER_GRANT_FRAME * nr_grant_frames;

	     i < GREFS_PER_GRANT_FRAME * new_nr_grant_frames - 1; i++)

	for (i = grefs_per_grant_frame * nr_grant_frames;

	     i < grefs_per_grant_frame * new_nr_grant_frames - 1; i++)

		gnttab_entry(i) = i + 1;



	gnttab_entry(i) = gnttab_free_head;

	gnttab_free_head = GREFS_PER_GRANT_FRAME * nr_grant_frames;

	gnttab_free_head = grefs_per_grant_frame * nr_grant_frames;

	gnttab_free_count += extra_entries;



	nr_grant_frames = new_nr_grant_frames;
@@ -957,7 +956,8 @@ EXPORT_SYMBOL_GPL(gnttab_unmap_refs); 


static unsigned nr_status_frames(unsigned nr_grant_frames)

{

	return (nr_grant_frames * GREFS_PER_GRANT_FRAME + SPP - 1) / SPP;

	BUG_ON(grefs_per_grant_frame == 0);

	return (nr_grant_frames * grefs_per_grant_frame + SPP - 1) / SPP;

}



static int gnttab_map_frames_v1(xen_pfn_t *frames, unsigned int nr_gframes)
@@ -1115,6 +1115,7 @@ static void gnttab_request_version(void) 
	rc = HYPERVISOR_grant_table_op(GNTTABOP_set_version, &gsv, 1);

	if (rc == 0 && gsv.version == 2) {

		grant_table_version = 2;

		grefs_per_grant_frame = PAGE_SIZE / sizeof(union grant_entry_v2);

		gnttab_interface = &gnttab_v2_ops;

	} else if (grant_table_version == 2) {

		/*
@@ -1127,17 +1128,17 @@ static void gnttab_request_version(void) 
		panic("we need grant tables version 2, but only version 1 is available");

	} else {

		grant_table_version = 1;

		grefs_per_grant_frame = PAGE_SIZE / sizeof(struct grant_entry_v1);

		gnttab_interface = &gnttab_v1_ops;

	}

	printk(KERN_INFO "Grant tables using version %d layout.\n",

		grant_table_version);

}



int gnttab_resume(void)

static int gnttab_setup(void)

{

	unsigned int max_nr_gframes;



	gnttab_request_version();

	max_nr_gframes = gnttab_max_grant_frames();

	if (max_nr_gframes < nr_grant_frames)

		return -ENOSYS;
@@ -1160,6 +1161,12 @@ int gnttab_resume(void) 
	return 0;

}



int gnttab_resume(void)

{

	gnttab_request_version();

	return gnttab_setup();

}



int gnttab_suspend(void)

{

	gnttab_interface->unmap_frames();
@@ -1171,9 +1178,10 @@ static int gnttab_expand(unsigned int req_entries) 
	int rc;

	unsigned int cur, extra;



	BUG_ON(grefs_per_grant_frame == 0);

	cur = nr_grant_frames;

	extra = ((req_entries + (GREFS_PER_GRANT_FRAME-1)) /

		 GREFS_PER_GRANT_FRAME);

	extra = ((req_entries + (grefs_per_grant_frame-1)) /

		 grefs_per_grant_frame);

	if (cur + extra > gnttab_max_grant_frames())

		return -ENOSPC;
@@ -1191,21 +1199,23 @@ int gnttab_init(void) 
	unsigned int nr_init_grefs;

	int ret;



	gnttab_request_version();

	nr_grant_frames = 1;

	boot_max_nr_grant_frames = __max_nr_grant_frames();



	/* Determine the maximum number of frames required for the

	 * grant reference free list on the current hypervisor.

	 */

	BUG_ON(grefs_per_grant_frame == 0);

	max_nr_glist_frames = (boot_max_nr_grant_frames *

			       GREFS_PER_GRANT_FRAME / RPP);

			       grefs_per_grant_frame / RPP);



	gnttab_list = kmalloc(max_nr_glist_frames * sizeof(grant_ref_t *),

			      GFP_KERNEL);

	if (gnttab_list == NULL)

		return -ENOMEM;



	nr_glist_frames = (nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;

	nr_glist_frames = (nr_grant_frames * grefs_per_grant_frame + RPP - 1) / RPP;

	for (i = 0; i < nr_glist_frames; i++) {

		gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_KERNEL);

		if (gnttab_list[i] == NULL) {
@@ -1214,12 +1224,12 @@ int gnttab_init(void) 
		}

	}



	if (gnttab_resume() < 0) {

	if (gnttab_setup() < 0) {

		ret = -ENODEV;

		goto ini_nomem;

	}



	nr_init_grefs = nr_grant_frames * GREFS_PER_GRANT_FRAME;

	nr_init_grefs = nr_grant_frames * grefs_per_grant_frame;



	for (i = NR_RESERVED_ENTRIES; i < nr_init_grefs - 1; i++)

		gnttab_entry(i) = i + 1;