Re: [Xen-devel] [PATCH xen v2] xen: arm: fully implement multicall interface.

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 04/07/2014 01:48 PM, Ian Campbell wrote:
> I'm not sure what I was smoking at the time of 5d74ad1a082e "xen: arm:
> implement do_multicall_call for both 32 and 64-bit" but it is obviously
> insufficient since it doesn't actually wire up the hypercall.
>
> Before doing so we need to make the usual adjustments for ARM and turn the
> unsigned longs into xen_ulong_t. There is no difference in the resulting
> structure for x86.
>
> There are knock on changes to the trace interface, but again they are nops on
> x86.
>
> For 32-bit ARM guests we require that the arguments which they pass to a
> hypercall via a multicall do not use the upper bits of xen_ulong_t and kill
> them if they violate this. This should ensure that no ABI surprises can be
> silently lurking when running on a 32-bit hypervisor waiting to pounce when the
> same kernel is run on a 64-bit hypervisor. Killing the guest is harsh but it
> will be far easier to relax the restriction if it turns out to cause problems
> than to tighten it up if we were lax to begin with.
>
> In the interests of clarity and always using explicitly sized types change the
> unsigned int in the hypercall arguments to a uint32_t. There is no actual
> change here on any platform.
>
> We should consider backporting this to 4.4.1 in case a guest decides they want
> to use a multicall in common code e.g. I suggested such a thing while
> reviewing a netback change recently.
>
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: keir@xxxxxxx
> Cc: jbeulich@xxxxxxxx
> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Trace-related bits:

Acked-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

> ---
> This depends on "xen: make sure that likely and unlikely convert the expression
> to a boolean"
>
> v2: - update compat version of __trace_multicall_call too
>      - update xen.h on requirements when sizeof(xen_ulong_t) > sizeof(a 
> register)
>      - kill 32-bit guests which do not follow those requirements. After the
>        conversation on v1 I decided that starting out harsh and relaxing if it
>        becomes a problem was easier than discovering a mistake later.
> ---
>   xen/arch/arm/traps.c          |   23 +++++++++++++++++++++--
>   xen/common/compat/multicall.c |    2 +-
>   xen/common/multicall.c        |    4 ++--
>   xen/common/trace.c            |    2 +-
>   xen/include/public/xen.h      |   10 ++++++----
>   xen/include/xen/trace.h       |    2 +-
>   6 files changed, 32 insertions(+), 11 deletions(-)
>
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index a7edc4e..062c4b5 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -1012,6 +1012,7 @@ static arm_hypercall_t arm_hypercall_table[] = {
>       HYPERCALL(sysctl, 2),
>       HYPERCALL(hvm_op, 2),
>       HYPERCALL(grant_table_op, 3),
> +    HYPERCALL(multicall, 2),
>       HYPERCALL_ARM(vcpu_op, 3),
>   };
>   
> @@ -1159,6 +1160,21 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, register_t *nr,
>   #endif
>   }
>   
> +static void check_multicall_32bit_clean(struct multicall_entry *multi)
> +{
> +    int i;
> +
> +    for ( i = 0; i < arm_hypercall_table[multi->op].nr_args; i++ )
> +    {
> +        if ( unlikely(multi->args[i] & 0xffffffff00000000ULL) )
> +        {
> +            printk("%pv: multicall argument %d is not 32-bit clean 
> %"PRIx64"\n",
> +                   current, i, multi->args[i]);
> +            domain_crash_synchronous();
> +        }
> +    }
> +}
> +
>   void do_multicall_call(struct multicall_entry *multi)
>   {
>       arm_hypercall_fn_t call = NULL;
> @@ -1176,9 +1192,12 @@ void do_multicall_call(struct multicall_entry *multi)
>           return;
>       }
>   
> +    if ( is_32bit_domain(current->domain) )
> +        check_multicall_32bit_clean(multi);
> +
>       multi->result = call(multi->args[0], multi->args[1],
> -                        multi->args[2], multi->args[3],
> -                        multi->args[4]);
> +                         multi->args[2], multi->args[3],
> +                         multi->args[4]);
>   }
>   
>   /*
> diff --git a/xen/common/compat/multicall.c b/xen/common/compat/multicall.c
> index 95c047a..2af8aef 100644
> --- a/xen/common/compat/multicall.c
> +++ b/xen/common/compat/multicall.c
> @@ -29,7 +29,7 @@ DEFINE_XEN_GUEST_HANDLE(multicall_entry_compat_t);
>   
>   static void __trace_multicall_call(multicall_entry_t *call)
>   {
> -    unsigned long args[6];
> +    xen_ulong_t args[6];
>       int i;
>   
>       for ( i = 0; i < ARRAY_SIZE(args); i++ )
> diff --git a/xen/common/multicall.c b/xen/common/multicall.c
> index e66c798..fa9d910 100644
> --- a/xen/common/multicall.c
> +++ b/xen/common/multicall.c
> @@ -35,10 +35,10 @@ static void trace_multicall_call(multicall_entry_t *call)
>   
>   ret_t
>   do_multicall(
> -    XEN_GUEST_HANDLE_PARAM(multicall_entry_t) call_list, unsigned int nr_calls)
> +    XEN_GUEST_HANDLE_PARAM(multicall_entry_t) call_list, uint32_t nr_calls)
>   {
>       struct mc_state *mcs = &current->mc_state;
> -    unsigned int     i;
> +    uint32_t         i;
>       int              rc = 0;
>   
>       if ( unlikely(__test_and_set_bit(_MCSF_in_multicall, &mcs->flags)) )
> diff --git a/xen/common/trace.c b/xen/common/trace.c
> index 1814165..f651cf3 100644
> --- a/xen/common/trace.c
> +++ b/xen/common/trace.c
> @@ -817,7 +817,7 @@ unlock:
>   }
>   
>   void __trace_hypercall(uint32_t event, unsigned long op,
> -                       const unsigned long *args)
> +                       const xen_ulong_t *args)
>   {
>       struct __packed {
>           uint32_t op;
> diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
> index 8c5697e..a6a2092 100644
> --- a/xen/include/public/xen.h
> +++ b/xen/include/public/xen.h
> @@ -541,13 +541,15 @@ DEFINE_XEN_GUEST_HANDLE(mmu_update_t);
>   /*
>    * ` enum neg_errnoval
>    * ` HYPERVISOR_multicall(multicall_entry_t call_list[],
> - * `                      unsigned int nr_calls);
> + * `                      uint32_t nr_calls);
>    *
> - * NB. The fields are natural register size for this architecture.
> + * NB. The fields are logically the natural register size for this
> + * architecture. In cases where xen_ulong_t is larger than this then
> + * any unused bits in the upper portion must be zero.
>    */
>   struct multicall_entry {
> -    unsigned long op, result;
> -    unsigned long args[6];
> +    xen_ulong_t op, result;
> +    xen_ulong_t args[6];
>   };
>   typedef struct multicall_entry multicall_entry_t;
>   DEFINE_XEN_GUEST_HANDLE(multicall_entry_t);
> diff --git a/xen/include/xen/trace.h b/xen/include/xen/trace.h
> index 3b8a7b3..12966ea 100644
> --- a/xen/include/xen/trace.h
> +++ b/xen/include/xen/trace.h
> @@ -45,7 +45,7 @@ static inline void trace_var(u32 event, int cycles, int extra,
>   }
>   
>   void __trace_hypercall(uint32_t event, unsigned long op,
> -                       const unsigned long *args);
> +                       const xen_ulong_t *args);
>   
>   /* Convenience macros for calling the trace function. */
>   #define TRACE_0D(_e)                            \

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