Re: [PATCH] xen/grant-table: correctly initialize grant table version 1

[ANNIE LI <annie.li@oracle.com>]

On 2012-12-20 4:20, Matt Wilson wrote:
> Commit 85ff6acb075a484780b3d763fdf41596d8fc0970 (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.

Correct.

>
> 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.

Thanks for posting this.
This is caused by not initializing grant_table_version in gnttab_init() 
before gnttab_resume(). How about only adding gnttab_request_version() 
and BUG_ON() to check grant_table_version in gnttab_init(), then no need 
to change GREFS_PER_GRANT_FRAME into grefs_per_grant_frame and add more 
BUG_ON() to check grefs_per_grant_frame?

For example, in gnttab_init()
....

+gnttab_request_version();
+BUG_ON(grant_table_version == 0);

....

Thanks
Annie
>
> Signed-off-by: Matt Wilson<msw@amazon.com>
> Reviewed-and-Tested-by: Steven Noonan<snoonan@amazon.com>
> Cc: Konrad Rzeszutek Wilk<konrad.wilk@oracle.com>
> Cc: Annie Li<annie.li@oracle.com>
> Cc: xen-devel@lists.xen.org
> ---
>   drivers/xen/grant-table.c |   41 +++++++++++++++++++++++------------------
>   1 files changed, 23 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index 043bf07..011fdc3 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -55,10 +55,6 @@
>   /* 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;
> @@ -153,6 +149,7 @@ 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;
>
> @@ -766,12 +763,14 @@ 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])
> @@ -779,12 +778,12 @@ 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;
> @@ -904,7 +903,8 @@ 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)
> @@ -1068,6 +1068,7 @@ 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) {
>   		/*
> @@ -1080,10 +1081,9 @@ 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)
> @@ -1092,6 +1092,8 @@ int gnttab_resume(void)
>   	char *kmsg = "Failed to kmalloc pages for pv in hvm grant frames\n";
>
>   	gnttab_request_version();
> +	printk(KERN_INFO "Grant tables using version %d layout.\n",
> +		grant_table_version);
>   	max_nr_gframes = gnttab_max_grant_frames();
>   	if (max_nr_gframes<  nr_grant_frames)
>   		return -ENOSYS;
> @@ -1137,9 +1139,10 @@ 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;
>
> @@ -1157,21 +1160,23 @@ 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) {
> @@ -1185,7 +1190,7 @@ int gnttab_init(void)
>   		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;