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xen/blkfront: don't use gnttab_query_foreign_access() for mapped status

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It isn't enough to check whether a grant is still being in use by
calling gnttab_query_foreign_access(), as a mapping could be realized
by the other side just after having called that function.

In case the call was done in preparation of revoking a grant it is
better to do so via gnttab_end_foreign_access_ref() and check the
success of that operation instead.

For the ring allocation use alloc_pages_exact() in order to avoid
high order pages in case of a multi-page ring.

If a grant wasn't unmapped by the backend without persistent grants
being used, set the device state to "error".

This is CVE-2022-23036 / part of XSA-396.

Reported-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
---
V2:
- use gnttab_try_end_foreign_access()
V4:
- use alloc_pages_exact() and free_pages_exact()
- set state to error if backend didn't unmap (Roger Pau Monné)
This commit is contained in:
Juergen Gross 2022-03-07 09:48:54 +01:00
parent 6b1775f26a
commit abf1fd5919
1 changed files with 37 additions and 26 deletions
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63
drivers/block/xen-blkfront.c
View File

@ -1288,7 +1288,8 @@ free_shadow:
rinfo->ring_ref[i] = GRANT_INVALID_REF;
}
}
free_pages((unsigned long)rinfo->ring.sring, get_order(info->nr_ring_pages * XEN_PAGE_SIZE));
free_pages_exact(rinfo->ring.sring,
info->nr_ring_pages * XEN_PAGE_SIZE);
rinfo->ring.sring = NULL;
if (rinfo->irq)
@ -1372,9 +1373,15 @@ static int blkif_get_final_status(enum blk_req_status s1,
return BLKIF_RSP_OKAY;
}
static bool blkif_completion(unsigned long *id,
struct blkfront_ring_info *rinfo,
struct blkif_response *bret)
/*
* Return values:
* 1 response processed.
* 0 missing further responses.
* -1 error while processing.
*/
static int blkif_completion(unsigned long *id,
struct blkfront_ring_info *rinfo,
struct blkif_response *bret)
{
int i = 0;
struct scatterlist *sg;
@ -1397,7 +1404,7 @@ static bool blkif_completion(unsigned long *id,
/* Wait the second response if not yet here. */
if (s2->status < REQ_DONE)
return false;
return 0;
bret->status = blkif_get_final_status(s->status,
s2->status);
@ -1448,42 +1455,43 @@ static bool blkif_completion(unsigned long *id,
}
/* Add the persistent grant into the list of free grants */
for (i = 0; i < num_grant; i++) {
if (gnttab_query_foreign_access(s->grants_used[i]->gref)) {
if (!gnttab_try_end_foreign_access(s->grants_used[i]->gref)) {
/*
* If the grant is still mapped by the backend (the
* backend has chosen to make this grant persistent)
* we add it at the head of the list, so it will be
* reused first.
*/
if (!info->feature_persistent)
pr_alert_ratelimited("backed has not unmapped grant: %u\n",
s->grants_used[i]->gref);
if (!info->feature_persistent) {
pr_alert("backed has not unmapped grant: %u\n",
s->grants_used[i]->gref);
return -1;
}
list_add(&s->grants_used[i]->node, &rinfo->grants);
rinfo->persistent_gnts_c++;
} else {
/*
* If the grant is not mapped by the backend we end the
* foreign access and add it to the tail of the list,
* so it will not be picked again unless we run out of
* persistent grants.
* If the grant is not mapped by the backend we add it
* to the tail of the list, so it will not be picked
* again unless we run out of persistent grants.
*/
gnttab_end_foreign_access(s->grants_used[i]->gref, 0, 0UL);
s->grants_used[i]->gref = GRANT_INVALID_REF;
list_add_tail(&s->grants_used[i]->node, &rinfo->grants);
}
}
if (s->req.operation == BLKIF_OP_INDIRECT) {
for (i = 0; i < INDIRECT_GREFS(num_grant); i++) {
if (gnttab_query_foreign_access(s->indirect_grants[i]->gref)) {
if (!info->feature_persistent)
pr_alert_ratelimited("backed has not unmapped grant: %u\n",
s->indirect_grants[i]->gref);
if (!gnttab_try_end_foreign_access(s->indirect_grants[i]->gref)) {
if (!info->feature_persistent) {
pr_alert("backed has not unmapped grant: %u\n",
s->indirect_grants[i]->gref);
return -1;
}
list_add(&s->indirect_grants[i]->node, &rinfo->grants);
rinfo->persistent_gnts_c++;
} else {
struct page *indirect_page;
gnttab_end_foreign_access(s->indirect_grants[i]->gref, 0, 0UL);
/*
* Add the used indirect page back to the list of
* available pages for indirect grefs.
@ -1498,7 +1506,7 @@ static bool blkif_completion(unsigned long *id,
}
}
return true;
return 1;
}
static irqreturn_t blkif_interrupt(int irq, void *dev_id)
@ -1564,12 +1572,17 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
}
if (bret.operation != BLKIF_OP_DISCARD) {
int ret;
/*
* We may need to wait for an extra response if the
* I/O request is split in 2
*/
if (!blkif_completion(&id, rinfo, &bret))
ret = blkif_completion(&id, rinfo, &bret);
if (!ret)
continue;
if (unlikely(ret < 0))
goto err;
}
if (add_id_to_freelist(rinfo, id)) {
@ -1676,8 +1689,7 @@ static int setup_blkring(struct xenbus_device *dev,
for (i = 0; i < info->nr_ring_pages; i++)
rinfo->ring_ref[i] = GRANT_INVALID_REF;
sring = (struct blkif_sring *)__get_free_pages(GFP_NOIO | __GFP_HIGH,
get_order(ring_size));
sring = alloc_pages_exact(ring_size, GFP_NOIO);
if (!sring) {
xenbus_dev_fatal(dev, -ENOMEM, "allocating shared ring");
return -ENOMEM;
@ -1687,7 +1699,7 @@ static int setup_blkring(struct xenbus_device *dev,
err = xenbus_grant_ring(dev, rinfo->ring.sring, info->nr_ring_pages, gref);
if (err < 0) {
free_pages((unsigned long)sring, get_order(ring_size));
free_pages_exact(sring, ring_size);
rinfo->ring.sring = NULL;
goto fail;
}
@ -2532,11 +2544,10 @@ static void purge_persistent_grants(struct blkfront_info *info)
list_for_each_entry_safe(gnt_list_entry, tmp, &rinfo->grants,
node) {
if (gnt_list_entry->gref == GRANT_INVALID_REF ||
gnttab_query_foreign_access(gnt_list_entry->gref))
!gnttab_try_end_foreign_access(gnt_list_entry->gref))
continue;
list_del(&gnt_list_entry->node);
gnttab_end_foreign_access(gnt_list_entry->gref, 0, 0UL);
rinfo->persistent_gnts_c--;
gnt_list_entry->gref = GRANT_INVALID_REF;
list_add_tail(&gnt_list_entry->node, &rinfo->grants);