Re: [Xen-devel] PING: [PATCH v3] arch/x86: Add registers to vm_event

[Alexandru Stefan ISAILA <aisaila@xxxxxxxxxxxxxxx>]

Any thoughts on this are appreciated.

Thanks,
Alex

On 18.10.2018 12:02, Alexandru Stefan ISAILA wrote:
> This patch adds a couple of regs to the vm_event that are used by
> the introspection. The base, limit and ar
> bits are compressed into a uint64_t union so as not to enlarge the
> vm_event.
> 
> Signed-off-by: Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>
> 
> ---
> Changes since V2:
>       - Keep fs/gs_base in 64bit long format
>       - Pull the sel out of x86_selector_reg
>       - Reformat limit field assignment
>       - Redesigned vm_event_pack_segment_register().
> ---
>   xen/arch/x86/vm_event.c       | 65 ++++++++++++++++++++++++++++++-----
>   xen/include/public/vm_event.h | 29 ++++++++++++++--
>   2 files changed, 84 insertions(+), 10 deletions(-)
> 
> diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
> index 15de43c3e6..803f97011b 100644
> --- a/xen/arch/x86/vm_event.c
> +++ b/xen/arch/x86/vm_event.c
> @@ -122,11 +122,60 @@ void vm_event_monitor_next_interrupt(struct vcpu *v)
>       v->arch.monitor.next_interrupt_enabled = true;
>   }
>   
> +static void vm_event_pack_segment_register(enum x86_segment segment,
> +                                           struct vm_event_regs_x86 *reg)
> +{
> +    struct segment_register seg;
> +
> +    hvm_get_segment_register(current, segment, &seg);
> +
> +    switch ( segment )
> +    {
> +    case x86_seg_ss:
> +        reg->ss.fields.base = seg.base;
> +        reg->ss.fields.limit = seg.g ? seg.limit >> 12 : seg.limit;
> +        reg->ss.fields.ar = seg.attr;
> +        reg->ss_sel = seg.sel;
> +        break;
> +    case x86_seg_fs:
> +        reg->fs_base = seg.base;
> +        reg->fs.fields.limit = seg.g ? seg.limit >> 12 : seg.limit;
> +        reg->fs.fields.ar = seg.attr;
> +        reg->fs_sel = seg.sel;
> +        break;
> +    case x86_seg_gs:
> +        reg->gs_base = seg.base;
> +        reg->gs.fields.limit = seg.g ? seg.limit >> 12 : seg.limit;
> +        reg->gs.fields.ar = seg.attr;
> +        reg->gs_sel = seg.sel;
> +        break;
> +    case x86_seg_cs:
> +        reg->cs.fields.base = seg.base;
> +        reg->cs.fields.limit = seg.g ? seg.limit >> 12 : seg.limit;
> +        reg->cs.fields.ar = seg.attr;
> +        reg->cs_sel = seg.sel;
> +        break;
> +    case x86_seg_ds:
> +        reg->ds.fields.base = seg.base;
> +        reg->ds.fields.limit = seg.g ? seg.limit >> 12 : seg.limit;
> +        reg->ds.fields.ar = seg.attr;
> +        reg->ds_sel = seg.sel;
> +        break;
> +    case x86_seg_es:
> +        reg->es.fields.base = seg.base;
> +        reg->es.fields.limit = seg.g ? seg.limit >> 12 : seg.limit;
> +        reg->es.fields.ar = seg.attr;
> +        reg->es_sel = seg.sel;
> +        break;
> +    default:
> +        break;
> +    }
> +}
> +
>   void vm_event_fill_regs(vm_event_request_t *req)
>   {
>   #ifdef CONFIG_HVM
>       const struct cpu_user_regs *regs = guest_cpu_user_regs();
> -    struct segment_register seg;
>       struct hvm_hw_cpu ctxt = {};
>       struct vcpu *curr = current;
>   
> @@ -170,14 +219,14 @@ void vm_event_fill_regs(vm_event_request_t *req)
>       req->data.regs.x86.msr_star = ctxt.msr_star;
>       req->data.regs.x86.msr_lstar = ctxt.msr_lstar;
>   
> -    hvm_get_segment_register(curr, x86_seg_fs, &seg);
> -    req->data.regs.x86.fs_base = seg.base;
> -
> -    hvm_get_segment_register(curr, x86_seg_gs, &seg);
> -    req->data.regs.x86.gs_base = seg.base;
> +    vm_event_pack_segment_register(x86_seg_fs, &req->data.regs.x86);
> +    vm_event_pack_segment_register(x86_seg_gs, &req->data.regs.x86);
> +    vm_event_pack_segment_register(x86_seg_cs, &req->data.regs.x86);
> +    vm_event_pack_segment_register(x86_seg_ss, &req->data.regs.x86);
> +    vm_event_pack_segment_register(x86_seg_ds, &req->data.regs.x86);
> +    vm_event_pack_segment_register(x86_seg_es, &req->data.regs.x86);
>   
> -    hvm_get_segment_register(curr, x86_seg_cs, &seg);
> -    req->data.regs.x86.cs_arbytes = seg.attr;
> +    req->data.regs.x86.shadow_gs = ctxt.shadow_gs;
>   #endif
>   }
>   
> diff --git a/xen/include/public/vm_event.h b/xen/include/public/vm_event.h
> index 36e3f4685d..0415ea607d 100644
> --- a/xen/include/public/vm_event.h
> +++ b/xen/include/public/vm_event.h
> @@ -29,7 +29,7 @@
>   
>   #include "xen.h"
>   
> -#define VM_EVENT_INTERFACE_VERSION 0x00000003
> +#define VM_EVENT_INTERFACE_VERSION 0x00000004
>   
>   #if defined(__XEN__) || defined(__XEN_TOOLS__)
>   
> @@ -157,6 +157,19 @@
>   #define VM_EVENT_X86_CR4    2
>   #define VM_EVENT_X86_XCR0   3
>   
> +struct x86_selector_reg {
> +    union
> +    {
> +        uint64_t bytes;
> +        struct
> +        {
> +            uint32_t base;
> +            uint32_t limit  :    20;
> +            uint32_t ar     :    12;
> +        } fields;
> +    };
> +};
> +
>   /*
>    * Using custom vCPU structs (i.e. not hvm_hw_cpu) for both x86 and ARM
>    * so as to not fill the vm_event ring buffer too quickly.
> @@ -193,7 +206,19 @@ struct vm_event_regs_x86 {
>       uint64_t msr_lstar;
>       uint64_t fs_base;
>       uint64_t gs_base;
> -    uint32_t cs_arbytes;
> +    struct x86_selector_reg cs;
> +    struct x86_selector_reg ss;
> +    struct x86_selector_reg ds;
> +    struct x86_selector_reg es;
> +    struct x86_selector_reg fs;
> +    struct x86_selector_reg gs;
> +    uint64_t shadow_gs;
> +    uint16_t cs_sel;
> +    uint16_t ss_sel;
> +    uint16_t ds_sel;
> +    uint16_t es_sel;
> +    uint16_t fs_sel;
> +    uint16_t gs_sel;
>       uint32_t _pad;
>   };
>   
> 
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