From: Juergen Gross Date: Thu, 7 Nov 2019 11:15:45 +0000 (+0100) Subject: xen/gntdev: replace global limit of mapped pages by limit per call X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=3b06ac6707c196b5036fe013c460da86c9060085;p=openwrt%2Fstaging%2Fblogic.git xen/gntdev: replace global limit of mapped pages by limit per call Today there is a global limit of pages mapped via /dev/xen/gntdev set to 1 million pages per default. There is no reason why that limit is existing, as total number of grant mappings is limited by the hypervisor anyway and preferring kernel mappings over userspace ones doesn't make sense. It should be noted that the gntdev device is usable by root only. Additionally checking of that limit is fragile, as the number of pages to map via one call is specified in a 32-bit unsigned variable which isn't tested to stay within reasonable limits (the only test is the value to be <= zero, which basically excludes only calls without any mapping requested). So trying to map e.g. 0xffff0000 pages while already nearly 1000000 pages are mapped will effectively lower the global number of mapped pages such that a parallel call mapping a reasonable amount of pages can succeed in spite of the global limit being violated. So drop the global limit and introduce per call limit instead. This per call limit (default: 65536 grant mappings) protects against allocating insane large arrays in the kernel for doing a hypercall which will fail anyway in case a user is e.g. trying to map billions of pages. Signed-off-by: Juergen Gross Reviewed-by: Oleksandr Andrushchenko Reviewed-by: Boris Ostrovsky Signed-off-by: Juergen Gross --- diff --git a/drivers/xen/gntdev-common.h b/drivers/xen/gntdev-common.h index 91e44c04f787..9a3960ecff6c 100644 --- a/drivers/xen/gntdev-common.h +++ b/drivers/xen/gntdev-common.h @@ -81,7 +81,7 @@ void gntdev_add_map(struct gntdev_priv *priv, struct gntdev_grant_map *add); void gntdev_put_map(struct gntdev_priv *priv, struct gntdev_grant_map *map); -bool gntdev_account_mapped_pages(int count); +bool gntdev_test_page_count(unsigned int count); int gntdev_map_grant_pages(struct gntdev_grant_map *map); diff --git a/drivers/xen/gntdev-dmabuf.c b/drivers/xen/gntdev-dmabuf.c index 2c4f324f8626..63f0857bf62d 100644 --- a/drivers/xen/gntdev-dmabuf.c +++ b/drivers/xen/gntdev-dmabuf.c @@ -446,7 +446,7 @@ dmabuf_exp_alloc_backing_storage(struct gntdev_priv *priv, int dmabuf_flags, { struct gntdev_grant_map *map; - if (unlikely(count <= 0)) + if (unlikely(gntdev_test_page_count(count))) return ERR_PTR(-EINVAL); if ((dmabuf_flags & GNTDEV_DMA_FLAG_WC) && @@ -459,11 +459,6 @@ dmabuf_exp_alloc_backing_storage(struct gntdev_priv *priv, int dmabuf_flags, if (!map) return ERR_PTR(-ENOMEM); - if (unlikely(gntdev_account_mapped_pages(count))) { - pr_debug("can't map %d pages: over limit\n", count); - gntdev_put_map(NULL, map); - return ERR_PTR(-ENOMEM); - } return map; } @@ -771,7 +766,7 @@ long gntdev_ioctl_dmabuf_exp_from_refs(struct gntdev_priv *priv, int use_ptemod, if (copy_from_user(&op, u, sizeof(op)) != 0) return -EFAULT; - if (unlikely(op.count <= 0)) + if (unlikely(gntdev_test_page_count(op.count))) return -EINVAL; refs = kcalloc(op.count, sizeof(*refs), GFP_KERNEL); @@ -818,7 +813,7 @@ long gntdev_ioctl_dmabuf_imp_to_refs(struct gntdev_priv *priv, if (copy_from_user(&op, u, sizeof(op)) != 0) return -EFAULT; - if (unlikely(op.count <= 0)) + if (unlikely(gntdev_test_page_count(op.count))) return -EINVAL; gntdev_dmabuf = dmabuf_imp_to_refs(priv->dmabuf_priv, diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c index 3d40f8074dbb..ad621ec1912c 100644 --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -55,12 +55,10 @@ MODULE_AUTHOR("Derek G. Murray , " "Gerd Hoffmann "); MODULE_DESCRIPTION("User-space granted page access driver"); -static int limit = 1024*1024; -module_param(limit, int, 0644); -MODULE_PARM_DESC(limit, "Maximum number of grants that may be mapped by " - "the gntdev device"); - -static atomic_t pages_mapped = ATOMIC_INIT(0); +static unsigned int limit = 64*1024; +module_param(limit, uint, 0644); +MODULE_PARM_DESC(limit, + "Maximum number of grants that may be mapped by one mapping request"); static int use_ptemod; @@ -71,9 +69,9 @@ static struct miscdevice gntdev_miscdev; /* ------------------------------------------------------------------ */ -bool gntdev_account_mapped_pages(int count) +bool gntdev_test_page_count(unsigned int count) { - return atomic_add_return(count, &pages_mapped) > limit; + return !count || count > limit; } static void gntdev_print_maps(struct gntdev_priv *priv, @@ -241,8 +239,6 @@ void gntdev_put_map(struct gntdev_priv *priv, struct gntdev_grant_map *map) if (!refcount_dec_and_test(&map->users)) return; - atomic_sub(map->count, &pages_mapped); - if (map->notify.flags & UNMAP_NOTIFY_SEND_EVENT) { notify_remote_via_evtchn(map->notify.event); evtchn_put(map->notify.event); @@ -568,7 +564,7 @@ static long gntdev_ioctl_map_grant_ref(struct gntdev_priv *priv, if (copy_from_user(&op, u, sizeof(op)) != 0) return -EFAULT; pr_debug("priv %p, add %d\n", priv, op.count); - if (unlikely(op.count <= 0)) + if (unlikely(gntdev_test_page_count(op.count))) return -EINVAL; err = -ENOMEM; @@ -576,12 +572,6 @@ static long gntdev_ioctl_map_grant_ref(struct gntdev_priv *priv, if (!map) return err; - if (unlikely(gntdev_account_mapped_pages(op.count))) { - pr_debug("can't map: over limit\n"); - gntdev_put_map(NULL, map); - return err; - } - if (copy_from_user(map->grants, &u->refs, sizeof(map->grants[0]) * op.count) != 0) { gntdev_put_map(NULL, map);