Re: [PATCH v9 6/8] common/domain: add a domain context record for shared_info...

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 24/09/2020 14:10, Paul Durrant wrote:
> diff --git a/tools/misc/xen-domctx.c b/tools/misc/xen-domctx.c
> index 243325dfce..6ead7ea89d 100644
> --- a/tools/misc/xen-domctx.c
> +++ b/tools/misc/xen-domctx.c
> @@ -31,6 +31,7 @@
>  #include <errno.h>
>  
>  #include <xenctrl.h>
> +#include <xen-tools/libs.h>
>  #include <xen/xen.h>
>  #include <xen/domctl.h>
>  #include <xen/save.h>
> @@ -61,6 +62,82 @@ static void dump_header(void)
>  
>  }
>  
> +static void print_binary(const char *prefix, const void *val, size_t size,
> +                         const char *suffix)
> +{
> +    printf("%s", prefix);
> +
> +    while ( size-- )
> +    {
> +        uint8_t octet = *(const uint8_t *)val++;
> +        unsigned int i;
> +
> +        for ( i = 0; i < 8; i++ )
> +        {
> +            printf("%u", octet & 1);
> +            octet >>= 1;
> +        }
> +    }
> +
> +    printf("%s", suffix);
> +}
> +
> +static void dump_shared_info(void)
> +{
> +    DOMAIN_SAVE_TYPE(SHARED_INFO) *s;
> +    bool has_32bit_shinfo;
> +    shared_info_any_t *info;
> +    unsigned int i, n;
> +
> +    GET_PTR(s);
> +    has_32bit_shinfo = s->flags & DOMAIN_SAVE_32BIT_SHINFO;
> +
> +    printf("    SHARED_INFO: has_32bit_shinfo: %s buffer_size: %u\n",
> +           has_32bit_shinfo ? "true" : "false", s->buffer_size);
> +
> +    info = (shared_info_any_t *)s->buffer;
> +
> +#define GET_FIELD_PTR(_f)            \
> +    (has_32bit_shinfo ?              \
> +     (const void *)&(info->x32._f) : \
> +     (const void *)&(info->x64._f))
> +#define GET_FIELD_SIZE(_f) \
> +    (has_32bit_shinfo ? sizeof(info->x32._f) : sizeof(info->x64._f))
> +#define GET_FIELD(_f) \
> +    (has_32bit_shinfo ? info->x32._f : info->x64._f)
> +
> +    n = has_32bit_shinfo ?
> +        ARRAY_SIZE(info->x32.evtchn_pending) :
> +        ARRAY_SIZE(info->x64.evtchn_pending);
> +
> +    for ( i = 0; i < n; i++ )
> +    {
> +        const char *prefix = !i ?
> +            "                 evtchn_pending: " :
> +            "                                 ";
> +
> +        print_binary(prefix, GET_FIELD_PTR(evtchn_pending[0]),
> +                 GET_FIELD_SIZE(evtchn_pending[0]), "\n");
> +    }
> +
> +    for ( i = 0; i < n; i++ )
> +    {
> +        const char *prefix = !i ?
> +            "                    evtchn_mask: " :
> +            "                                 ";
> +
> +        print_binary(prefix, GET_FIELD_PTR(evtchn_mask[0]),
> +                 GET_FIELD_SIZE(evtchn_mask[0]), "\n");
> +    }

What about domains using FIFO?  This is meaningless for them.

> +
> +    printf("                 wc: version: %u sec: %u nsec: %u\n",
> +           GET_FIELD(wc_version), GET_FIELD(wc_sec), GET_FIELD(wc_nsec));

wc_sec_hi is also a rather critical field in this calculation.

> +
> +#undef GET_FIELD
> +#undef GET_FIELD_SIZE
> +#undef GET_FIELD_PTR
> +}
> +
>  static void dump_end(void)
>  {
>      DOMAIN_SAVE_TYPE(END) *e;
> @@ -173,6 +250,7 @@ int main(int argc, char **argv)
>              switch (desc->typecode)
>              {
>              case DOMAIN_SAVE_CODE(HEADER): dump_header(); break;
> +            case DOMAIN_SAVE_CODE(SHARED_INFO): dump_shared_info(); break;
>              case DOMAIN_SAVE_CODE(END): dump_end(); break;
>              default:
>                  printf("Unknown type %u: skipping\n", desc->typecode);
> diff --git a/xen/common/domain.c b/xen/common/domain.c
> index 8cfa2e0b6b..6709f9c79e 100644
> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -33,6 +33,7 @@
>  #include <xen/xenoprof.h>
>  #include <xen/irq.h>
>  #include <xen/argo.h>
> +#include <xen/save.h>
>  #include <asm/debugger.h>
>  #include <asm/p2m.h>
>  #include <asm/processor.h>
> @@ -1657,6 +1658,110 @@ int continue_hypercall_on_cpu(
>      return 0;
>  }
>  
> +static int save_shared_info(const struct domain *d, struct domain_context *c,
> +                            bool dry_run)
> +{
> +    struct domain_shared_info_context ctxt = {
> +#ifdef CONFIG_COMPAT
> +        .flags = has_32bit_shinfo(d) ? DOMAIN_SAVE_32BIT_SHINFO : 0,
> +        .buffer_size = has_32bit_shinfo(d) ?
> +                       sizeof(struct compat_shared_info) :
> +                       sizeof(struct shared_info),
> +#else
> +        .buffer_size = sizeof(struct shared_info),
> +#endif
> +    };
> +    size_t hdr_size = offsetof(typeof(ctxt), buffer);
> +    int rc;
> +
> +    rc = DOMAIN_SAVE_BEGIN(SHARED_INFO, c, 0);
> +    if ( rc )
> +        return rc;
> +
> +    rc = domain_save_data(c, &ctxt, hdr_size);
> +    if ( rc )
> +        return rc;
> +
> +    rc = domain_save_data(c, d->shared_info, ctxt.buffer_size);
> +    if ( rc )
> +        return rc;
> +
> +    return domain_save_end(c);
> +}
> +
> +static int load_shared_info(struct domain *d, struct domain_context *c)
> +{
> +    struct domain_shared_info_context ctxt;
> +    size_t hdr_size = offsetof(typeof(ctxt), buffer);
> +    unsigned int i;
> +    int rc;
> +
> +    rc = DOMAIN_LOAD_BEGIN(SHARED_INFO, c, &i);
> +    if ( rc )
> +        return rc;
> +
> +    if ( i ) /* expect only a single instance */
> +        return -ENXIO;
> +
> +    rc = domain_load_data(c, &ctxt, hdr_size);
> +    if ( rc )
> +        return rc;
> +
> +    if ( ctxt.buffer_size > sizeof(shared_info_t) ||
> +         (ctxt.flags & ~DOMAIN_SAVE_32BIT_SHINFO) )
> +        return -EINVAL;
> +
> +    if ( ctxt.flags & DOMAIN_SAVE_32BIT_SHINFO )
> +    {
> +#ifdef CONFIG_COMPAT
> +        has_32bit_shinfo(d) = true;

d->arch.has_32bit_shinfo

> +#else
> +        return -EINVAL;
> +#endif
> +    }
> +
> +    if ( is_pv_domain(d) )
> +    {
> +        shared_info_t *shinfo = xmalloc(shared_info_t);
> +
> +        if ( !shinfo )
> +            return -ENOMEM;
> +
> +        rc = domain_load_data(c, shinfo, sizeof(*shinfo));
> +        if ( rc )
> +            goto out;

There's no need for a memory allocation, or to double buffer this data. 
You can memcpy() straight out of the context record.

> +
> +        memcpy(&shared_info(d, vcpu_info), &__shared_info(d, shinfo, 
> vcpu_info),
> +               sizeof(shared_info(d, vcpu_info)));
> +        memcpy(&shared_info(d, arch), &__shared_info(d, shinfo, arch),
> +               sizeof(shared_info(d, arch)));
> +
> +        memset(&shared_info(d, evtchn_pending), 0,
> +               sizeof(shared_info(d, evtchn_pending)));
> +        memset(&shared_info(d, evtchn_mask), 0xff,
> +               sizeof(shared_info(d, evtchn_mask)));
> +
> +        shared_info(d, arch.pfn_to_mfn_frame_list_list) = 0;
> +        for ( i = 0; i < XEN_LEGACY_MAX_VCPUS; i++ )
> +            shared_info(d, vcpu_info[i].evtchn_pending_sel) = 0;

What is the plan for transparent migrate here?  While this is ok for
regular migrate, its definitely not for transparent.

> +
> +        rc = domain_load_end(c, false);
> +
> +    out:
> +        xfree(shinfo);
> +    }
> +    else
> +        /*
> +         * No modifications to shared_info are required for restoring non-PV
> +         * domains.
> +         */
> +        rc = domain_load_end(c, true);
> +
> +    return rc;
> +}
> +
> +DOMAIN_REGISTER_SAVE_LOAD(SHARED_INFO, save_shared_info, load_shared_info);
> +
>  /*
>   * Local variables:
>   * mode: C
> diff --git a/xen/include/public/save.h b/xen/include/public/save.h
> index 551dbbddb8..0e855a4b97 100644
> --- a/xen/include/public/save.h
> +++ b/xen/include/public/save.h
> @@ -82,7 +82,18 @@ struct domain_save_header {
>  };
>  DECLARE_DOMAIN_SAVE_TYPE(HEADER, 1, struct domain_save_header);
>  
> -#define DOMAIN_SAVE_CODE_MAX 1
> +struct domain_shared_info_context {
> +    uint32_t flags;
> +
> +#define DOMAIN_SAVE_32BIT_SHINFO 0x00000001
> +
> +    uint32_t buffer_size;

This struct is already wrapped with a header including a size which
encompasses buffer.

Multiple overlapping size fields is an easy way to memory corruption,
because it causes ambiguity as to which one is right.

~Andrew