Re: [PATCH 3/4] xen/arm, libxl: Revert XEN_DOMCTL_shadow_op; use p2m mempool hypercalls

[Stefano Stabellini <sstabellini@kernel.org>]

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On Wed, 26 Oct 2022, Andrew Cooper wrote:
> This reverts most of commit cf2a68d2ffbc3ce95e01449d46180bddb10d24a0, and bits
> of cbea5a1149ca7fd4b7cdbfa3ec2e4f109b601ff7.
> 
> First of all, with ARM borrowing x86's implementation, the logic to set the
> pool size should have been common, not duplicated.  Introduce
> libxl__domain_set_p2m_pool_size() as a shared implementation, and use it from
> the ARM and x86 paths.  It is left as an exercise to the reader to judge how
> libxl/xl can reasonably function without the ability to query the pool size...
> 
> Remove ARM's p2m_domctl() infrastructure now the functioanlity has been
> replaced with a working and unit tested interface.
> 
> This is part of XSA-409 / CVE-2022-33747.

Genuine question: I can see this patch removes the implementation of
XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION on ARM. It also switches libxl (both
ARM and x86) to the new hypercall.

Why keep the old hypercall (XEN_DOMCTL_shadow_op and
XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION) implementation on x86 (not on ARM)?

Is that because it was only recently implemented? And not actually
present in any past Xen release?

If so, please add a note about this in the commit message. Also, if that
is the case, I think this patch series should go in 4.17. If it is too
late to get it in before the release, then we should backport it to 4.17
as soon as possible. That's because ideally we want to keep the
hypercall interface changes down to a minimum.


> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> ---
> CC: Xen Security Team <security@xen.org>
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Roger Pau Monné <roger.pau@citrix.com>
> CC: Wei Liu <wl@xen.org>
> CC: Stefano Stabellini <sstabellini@kernel.org>
> CC: Julien Grall <julien@xen.org>
> CC: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
> CC: Bertrand Marquis <bertrand.marquis@arm.com>
> CC: Henry Wang <Henry.Wang@arm.com>
> CC: Anthony PERARD <anthony.perard@citrix.com>
> ---
>  tools/libs/light/libxl_arm.c      | 14 +----------
>  tools/libs/light/libxl_dom.c      | 19 ++++++++++++++
>  tools/libs/light/libxl_internal.h |  3 +++
>  tools/libs/light/libxl_x86.c      | 15 ++---------
>  xen/arch/arm/domctl.c             | 53 ---------------------------------------
>  xen/arch/arm/include/asm/p2m.h    |  1 -
>  xen/arch/arm/p2m.c                |  8 ------
>  7 files changed, 25 insertions(+), 88 deletions(-)
> 
> diff --git a/tools/libs/light/libxl_arm.c b/tools/libs/light/libxl_arm.c
> index 2a5e93c28403..2f5615263543 100644
> --- a/tools/libs/light/libxl_arm.c
> +++ b/tools/libs/light/libxl_arm.c
> @@ -209,19 +209,7 @@ int libxl__arch_domain_create(libxl__gc *gc,
>                                libxl__domain_build_state *state,
>                                uint32_t domid)
>  {
> -    libxl_ctx *ctx = libxl__gc_owner(gc);
> -    unsigned int shadow_mb = DIV_ROUNDUP(d_config->b_info.shadow_memkb, 1024);
> -
> -    int r = xc_shadow_control(ctx->xch, domid,
> -                              XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION,
> -                              &shadow_mb, 0);
> -    if (r) {
> -        LOGED(ERROR, domid,
> -              "Failed to set %u MiB shadow allocation", shadow_mb);
> -        return ERROR_FAIL;
> -    }
> -
> -    return 0;
> +    return libxl__domain_set_p2m_pool_size(gc, d_config, domid);
>  }
>  
>  int libxl__arch_extra_memory(libxl__gc *gc,
> diff --git a/tools/libs/light/libxl_dom.c b/tools/libs/light/libxl_dom.c
> index 2abaab439c4f..f93b221f1c1f 100644
> --- a/tools/libs/light/libxl_dom.c
> +++ b/tools/libs/light/libxl_dom.c
> @@ -1448,6 +1448,25 @@ int libxl_userdata_unlink(libxl_ctx *ctx, uint32_t domid,
>      return rc;
>  }
>  
> +int libxl__domain_set_p2m_pool_size(
> +    libxl__gc *gc, libxl_domain_config *d_config, uint32_t domid)
> +{
> +    libxl_ctx *ctx = libxl__gc_owner(gc);
> +    uint64_t shadow_mem;
> +
> +    shadow_mem = d_config->b_info.shadow_memkb;
> +    shadow_mem <<= 10;
> +
> +    int r = xc_get_p2m_mempool_size(ctx->xch, domid, &shadow_mem);
> +    if (r) {
> +        LOGED(ERROR, domid,
> +              "Failed to set p2m pool size to %"PRIu64"kB", shadow_mem);
> +        return ERROR_FAIL;
> +    }
> +
> +    return 0;
> +}
> +
>  /*
>   * Local variables:
>   * mode: C
> diff --git a/tools/libs/light/libxl_internal.h b/tools/libs/light/libxl_internal.h
> index cb9e8b3b8b5a..f31164bc6c0d 100644
> --- a/tools/libs/light/libxl_internal.h
> +++ b/tools/libs/light/libxl_internal.h
> @@ -4864,6 +4864,9 @@ int libxl__is_domid_recent(libxl__gc *gc, uint32_t domid, bool *recent);
>  /* os-specific implementation of setresuid() */
>  int libxl__setresuid(uid_t ruid, uid_t euid, uid_t suid);
>  
> +_hidden int libxl__domain_set_p2m_pool_size(
> +    libxl__gc *gc, libxl_domain_config *d_config, uint32_t domid);
> +
>  #endif
>  
>  /*
> diff --git a/tools/libs/light/libxl_x86.c b/tools/libs/light/libxl_x86.c
> index 7c5ee74443e5..99aba51d05df 100644
> --- a/tools/libs/light/libxl_x86.c
> +++ b/tools/libs/light/libxl_x86.c
> @@ -538,20 +538,9 @@ int libxl__arch_domain_create(libxl__gc *gc,
>          xc_domain_set_time_offset(ctx->xch, domid, rtc_timeoffset);
>  
>      if (d_config->b_info.type != LIBXL_DOMAIN_TYPE_PV) {
> -        unsigned int shadow_mb = DIV_ROUNDUP(d_config->b_info.shadow_memkb,
> -                                             1024);
> -        int r = xc_shadow_control(ctx->xch, domid,
> -                                  XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION,
> -                                  &shadow_mb, 0);
> -
> -        if (r) {
> -            LOGED(ERROR, domid,
> -                  "Failed to set %u MiB %s allocation",
> -                  shadow_mb,
> -                  libxl_defbool_val(d_config->c_info.hap) ? "HAP" : "shadow");
> -            ret = ERROR_FAIL;
> +        ret = libxl__domain_set_p2m_pool_size(gc, d_config, domid);
> +        if (ret)
>              goto out;
> -        }
>      }
>  
>      if (d_config->c_info.type == LIBXL_DOMAIN_TYPE_PV &&
> diff --git a/xen/arch/arm/domctl.c b/xen/arch/arm/domctl.c
> index c8fdeb124084..1baf25c3d98b 100644
> --- a/xen/arch/arm/domctl.c
> +++ b/xen/arch/arm/domctl.c
> @@ -47,64 +47,11 @@ static int handle_vuart_init(struct domain *d,
>      return rc;
>  }
>  
> -static long p2m_domctl(struct domain *d, struct xen_domctl_shadow_op *sc,
> -                       XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
> -{
> -    long rc;
> -    bool preempted = false;
> -
> -    if ( unlikely(d == current->domain) )
> -    {
> -        printk(XENLOG_ERR "Tried to do a p2m domctl op on itself.\n");
> -        return -EINVAL;
> -    }
> -
> -    if ( unlikely(d->is_dying) )
> -    {
> -        printk(XENLOG_ERR "Tried to do a p2m domctl op on dying domain %u\n",
> -               d->domain_id);
> -        return -EINVAL;
> -    }
> -
> -    switch ( sc->op )
> -    {
> -    case XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION:
> -    {
> -        /* Allow and handle preemption */
> -        spin_lock(&d->arch.paging.lock);
> -        rc = p2m_set_allocation(d, sc->mb << (20 - PAGE_SHIFT), &preempted);
> -        spin_unlock(&d->arch.paging.lock);
> -
> -        if ( preempted )
> -            /* Not finished. Set up to re-run the call. */
> -            rc = hypercall_create_continuation(__HYPERVISOR_domctl, "h",
> -                                               u_domctl);
> -        else
> -            /* Finished. Return the new allocation. */
> -            sc->mb = p2m_get_allocation(d);
> -
> -        return rc;
> -    }
> -    case XEN_DOMCTL_SHADOW_OP_GET_ALLOCATION:
> -    {
> -        sc->mb = p2m_get_allocation(d);
> -        return 0;
> -    }
> -    default:
> -    {
> -        printk(XENLOG_ERR "Bad p2m domctl op %u\n", sc->op);
> -        return -EINVAL;
> -    }
> -    }
> -}
> -
>  long arch_do_domctl(struct xen_domctl *domctl, struct domain *d,
>                      XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
>  {
>      switch ( domctl->cmd )
>      {
> -    case XEN_DOMCTL_shadow_op:
> -        return p2m_domctl(d, &domctl->u.shadow_op, u_domctl);
>      case XEN_DOMCTL_cacheflush:
>      {
>          gfn_t s = _gfn(domctl->u.cacheflush.start_pfn);
> diff --git a/xen/arch/arm/include/asm/p2m.h b/xen/arch/arm/include/asm/p2m.h
> index c8f14d13c2c5..91df922e1c9f 100644
> --- a/xen/arch/arm/include/asm/p2m.h
> +++ b/xen/arch/arm/include/asm/p2m.h
> @@ -222,7 +222,6 @@ void p2m_restore_state(struct vcpu *n);
>  /* Print debugging/statistial info about a domain's p2m */
>  void p2m_dump_info(struct domain *d);
>  
> -unsigned int p2m_get_allocation(struct domain *d);
>  int p2m_set_allocation(struct domain *d, unsigned long pages, bool *preempted);
>  int p2m_teardown_allocation(struct domain *d);
>  
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 4607cde6f0b8..92b678cf0d09 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -92,14 +92,6 @@ static void p2m_free_page(struct domain *d, struct page_info *pg)
>      spin_unlock(&d->arch.paging.lock);
>  }
>  
> -/* Return the size of the pool, rounded up to the nearest MB */
> -unsigned int p2m_get_allocation(struct domain *d)
> -{
> -    unsigned long nr_pages = ACCESS_ONCE(d->arch.paging.p2m_total_pages);
> -
> -    return ROUNDUP(nr_pages, 1 << (20 - PAGE_SHIFT)) >> (20 - PAGE_SHIFT);
> -}
> -
>  /* Return the size of the pool, in bytes. */
>  int arch_get_p2m_mempool_size(struct domain *d, uint64_t *size)
>  {
> -- 
> 2.11.0
>