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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [PATCH v2 04/11] xen/memory: Fix acquire_resource size semantics
> -----Original Message-----
> From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Sent: 22 September 2020 19:25
> To: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>; George Dunlap
> <George.Dunlap@xxxxxxxxxxxxx>; Ian
> Jackson <iwj@xxxxxxxxxxxxxx>; Jan Beulich <JBeulich@xxxxxxxx>; Stefano
> Stabellini
> <sstabellini@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Julien Grall
> <julien@xxxxxxx>; Paul Durrant
> <paul@xxxxxxx>; Michał Leszczyński <michal.leszczynski@xxxxxxx>; Hubert
> Jasudowicz
> <hubert.jasudowicz@xxxxxxx>; Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
> Subject: [PATCH v2 04/11] xen/memory: Fix acquire_resource size semantics
>
> Calling XENMEM_acquire_resource with a NULL frame_list is a request for the
> size of the resource, but the returned 32 is bogus.
>
> If someone tries to follow it for XENMEM_resource_ioreq_server, the acquire
> call will fail as IOREQ servers currently top out at 2 frames, and it is only
> half the size of the default grant table limit for guests.
>
> Also, no users actually request a resource size, because it was never wired up
> in the sole implementaion of resource acquisition in Linux.
>
> Introduce a new resource_max_frames() to calculate the size of a resource, and
> implement it the IOREQ and grant subsystems.
>
> It is impossible to guarantee that a mapping call following a successful size
> call will succeed (e.g. The target IOREQ server gets destroyed, or the domain
> switches from grant v2 to v1). Document the restriction, and use the
> flexibility to simplify the paths to be lockless.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> CC: Ian Jackson <iwj@xxxxxxxxxxxxxx>
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Wei Liu <wl@xxxxxxx>
> CC: Julien Grall <julien@xxxxxxx>
> CC: Paul Durrant <paul@xxxxxxx>
> CC: Michał Leszczyński <michal.leszczynski@xxxxxxx>
> CC: Hubert Jasudowicz <hubert.jasudowicz@xxxxxxx>
> CC: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
>
> v2:
> * Spelling fixes
> * Add more local variables.
> * Don't return any status frames on ARM where v2 support is compiled out.
> ---
> xen/arch/x86/mm.c | 20 ++++++++++++++++
> xen/common/grant_table.c | 23 ++++++++++++++++++
> xen/common/memory.c | 55
> +++++++++++++++++++++++++++++++++----------
> xen/include/asm-x86/mm.h | 3 +++
> xen/include/public/memory.h | 16 +++++++++----
> xen/include/xen/grant_table.h | 8 +++++++
> xen/include/xen/mm.h | 6 +++++
> 7 files changed, 114 insertions(+), 17 deletions(-)
>
> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
> index d1cfc8fb4a..e82307bdae 100644
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -4591,6 +4591,26 @@ int xenmem_add_to_physmap_one(
> return rc;
> }
>
> +unsigned int arch_resource_max_frames(
> + struct domain *d, unsigned int type, unsigned int id)
> +{
> + unsigned int nr = 0;
> +
> + switch ( type )
> + {
> +#ifdef CONFIG_HVM
> + case XENMEM_resource_ioreq_server:
> + if ( !is_hvm_domain(d) )
> + break;
> + /* One frame for the buf-ioreq ring, and one frame per 128 vcpus. */
> + nr = 1 + DIV_ROUND_UP(d->max_vcpus * sizeof(struct ioreq),
> PAGE_SIZE);
The buf-ioreq ring is optional so a caller using this value may still get a
resource acquisition failure unless the id is used to actually look up and
check the ioreq server in question for the actual maximum. So this needs to
call into a new function in ioreq.c.
Paul
> + break;
> +#endif
> + }
> +
> + return nr;
> +}
> +
> int arch_acquire_resource(struct domain *d, unsigned int type,
> unsigned int id, unsigned long frame,
> unsigned int nr_frames, xen_pfn_t mfn_list[])
> diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
> index 912f07be47..8c401a5540 100644
> --- a/xen/common/grant_table.c
> +++ b/xen/common/grant_table.c
> @@ -4013,6 +4013,29 @@ static int gnttab_get_shared_frame_mfn(struct domain
> *d,
> return 0;
> }
>
> +unsigned int gnttab_resource_max_frames(struct domain *d, unsigned int id)
> +{
> + const struct grant_table *gt = d->grant_table;
> + unsigned int nr = 0;
> +
> + /* Don't need the grant lock. This limit is fixed at domain create
> time. */
> + switch ( id )
> + {
> + case XENMEM_resource_grant_table_id_shared:
> + nr = gt->max_grant_frames;
> + break;
> +
> + case XENMEM_resource_grant_table_id_status:
> + if ( GNTTAB_MAX_VERSION < 2 )
> + break;
> +
> + nr = grant_to_status_frames(gt->max_grant_frames);
> + break;
> + }
> +
> + return nr;
> +}
> +
> int gnttab_acquire_resource(
> struct domain *d, unsigned int id, unsigned long frame,
> unsigned int nr_frames, xen_pfn_t mfn_list[])
> diff --git a/xen/common/memory.c b/xen/common/memory.c
> index 177fc378d9..c559935732 100644
> --- a/xen/common/memory.c
> +++ b/xen/common/memory.c
> @@ -1007,6 +1007,26 @@ static long xatp_permission_check(struct domain *d,
> unsigned int space)
> return xsm_add_to_physmap(XSM_TARGET, current->domain, d);
> }
>
> +/*
> + * Return 0 on any kind of error. Caller converts to -EINVAL.
> + *
> + * All nonzero values should be repeatable (i.e. derived from some fixed
> + * property of the domain), and describe the full resource (i.e. mapping the
> + * result of this call will be the entire resource).
> + */
> +static unsigned int resource_max_frames(struct domain *d,
> + unsigned int type, unsigned int id)
> +{
> + switch ( type )
> + {
> + case XENMEM_resource_grant_table:
> + return gnttab_resource_max_frames(d, id);
> +
> + default:
> + return arch_resource_max_frames(d, type, id);
> + }
> +}
> +
> static int acquire_resource(
> XEN_GUEST_HANDLE_PARAM(xen_mem_acquire_resource_t) arg)
> {
> @@ -1018,6 +1038,7 @@ static int acquire_resource(
> * use-cases then per-CPU arrays or heap allocations may be required.
> */
> xen_pfn_t mfn_list[32];
> + unsigned int max_frames;
> int rc;
>
> /*
> @@ -1034,19 +1055,6 @@ static int acquire_resource(
> if ( xmar.pad != 0 )
> return -EINVAL;
>
> - if ( guest_handle_is_null(xmar.frame_list) )
> - {
> - if ( xmar.nr_frames )
> - return -EINVAL;
> -
> - xmar.nr_frames = ARRAY_SIZE(mfn_list);
> -
> - if ( __copy_field_to_guest(arg, &xmar, nr_frames) )
> - return -EFAULT;
> -
> - return 0;
> - }
> -
> if ( xmar.nr_frames > ARRAY_SIZE(mfn_list) )
> return -E2BIG;
>
> @@ -1058,6 +1066,27 @@ static int acquire_resource(
> if ( rc )
> goto out;
>
> + max_frames = resource_max_frames(d, xmar.type, xmar.id);
> +
> + rc = -EINVAL;
> + if ( !max_frames )
> + goto out;
> +
> + if ( guest_handle_is_null(xmar.frame_list) )
> + {
> + if ( xmar.nr_frames )
> + goto out;
> +
> + xmar.nr_frames = max_frames;
> +
> + rc = -EFAULT;
> + if ( __copy_field_to_guest(arg, &xmar, nr_frames) )
> + goto out;
> +
> + rc = 0;
> + goto out;
> + }
> +
> switch ( xmar.type )
> {
> case XENMEM_resource_grant_table:
> diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
> index deeba75a1c..13977652a8 100644
> --- a/xen/include/asm-x86/mm.h
> +++ b/xen/include/asm-x86/mm.h
> @@ -639,6 +639,9 @@ static inline bool arch_mfn_in_directmap(unsigned long
> mfn)
> return mfn <= (virt_to_mfn(eva - 1) + 1);
> }
>
> +unsigned int arch_resource_max_frames(struct domain *d,
> + unsigned int type, unsigned int id);
> +
> int arch_acquire_resource(struct domain *d, unsigned int type,
> unsigned int id, unsigned long frame,
> unsigned int nr_frames, xen_pfn_t mfn_list[]);
> diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
> index 21d483298e..d7eb34f167 100644
> --- a/xen/include/public/memory.h
> +++ b/xen/include/public/memory.h
> @@ -639,10 +639,18 @@ struct xen_mem_acquire_resource {
> #define XENMEM_resource_grant_table_id_status 1
>
> /*
> - * IN/OUT - As an IN parameter number of frames of the resource
> - * to be mapped. However, if the specified value is 0 and
> - * frame_list is NULL then this field will be set to the
> - * maximum value supported by the implementation on return.
> + * IN/OUT
> + *
> + * As an IN parameter number of frames of the resource to be mapped.
> + *
> + * When frame_list is NULL and nr_frames is 0, this is interpreted as a
> + * request for the size of the resource, which shall be returned in the
> + * nr_frames field.
> + *
> + * The size of a resource will never be zero, but a nonzero result
> doesn't
> + * guarantee that a subsequent mapping request will be successful. There
> + * are further type/id specific constraints which may change between the
> + * two calls.
> */
> uint32_t nr_frames;
> uint32_t pad;
> diff --git a/xen/include/xen/grant_table.h b/xen/include/xen/grant_table.h
> index 5a2c75b880..bae4d79623 100644
> --- a/xen/include/xen/grant_table.h
> +++ b/xen/include/xen/grant_table.h
> @@ -57,6 +57,8 @@ int mem_sharing_gref_to_gfn(struct grant_table *gt,
> grant_ref_t ref,
> int gnttab_map_frame(struct domain *d, unsigned long idx, gfn_t gfn,
> mfn_t *mfn);
>
> +unsigned int gnttab_resource_max_frames(struct domain *d, unsigned int id);
> +
> int gnttab_acquire_resource(
> struct domain *d, unsigned int id, unsigned long frame,
> unsigned int nr_frames, xen_pfn_t mfn_list[]);
> @@ -93,6 +95,12 @@ static inline int gnttab_map_frame(struct domain *d,
> unsigned long idx,
> return -EINVAL;
> }
>
> +static inline unsigned int gnttab_resource_max_frames(
> + struct domain *d, unsigned int id)
> +{
> + return 0;
> +}
> +
> static inline int gnttab_acquire_resource(
> struct domain *d, unsigned int id, unsigned long frame,
> unsigned int nr_frames, xen_pfn_t mfn_list[])
> diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
> index 26a4a3d350..d686876b0e 100644
> --- a/xen/include/xen/mm.h
> +++ b/xen/include/xen/mm.h
> @@ -686,6 +686,12 @@ static inline void put_page_alloc_ref(struct page_info
> *page)
> }
>
> #ifndef CONFIG_ARCH_ACQUIRE_RESOURCE
> +static inline unsigned int arch_resource_max_frames(
> + struct domain *d, unsigned int type, unsigned int id)
> +{
> + return 0;
> +}
> +
> static inline int arch_acquire_resource(
> struct domain *d, unsigned int type, unsigned int id, unsigned long
> frame,
> unsigned int nr_frames, xen_pfn_t mfn_list[])
> --
> 2.11.0
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