Re: [Xen-devel] [PATCH] x86/HVM: linear address must be canonical for the whole accessed range

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 20/09/2013 14:07, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> ... rather than just for the first byte.
> 
> While at it, also
> - make the real mode case at least dpo a wrap around check
> - drop the mis-named "gpf" label (we're not generating faults here)
>   and use in-place returns instead
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Keir Fraser <keir@xxxxxxx>

> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -1931,8 +1931,7 @@ int hvm_virtual_to_linear_addr(
>      unsigned int addr_size,
>      unsigned long *linear_addr)
>  {
> -    unsigned long addr = offset;
> -    uint32_t last_byte;
> +    unsigned long addr = offset, last_byte;
>  
>      if ( !(current->arch.hvm_vcpu.guest_cr[0] & X86_CR0_PE) )
>      {
> @@ -1941,6 +1940,9 @@ int hvm_virtual_to_linear_addr(
>           * Certain of them are not done in native real mode anyway.
>           */
>          addr = (uint32_t)(addr + reg->base);
> +        last_byte = (uint32_t)addr + bytes - 1;
> +        if ( last_byte < addr )
> +            return 0;
>      }
>      else if ( addr_size != 64 )
>      {
> @@ -1952,17 +1954,17 @@ int hvm_virtual_to_linear_addr(
>          {
>          case hvm_access_read:
>              if ( (reg->attr.fields.type & 0xa) == 0x8 )
> -                goto gpf; /* execute-only code segment */
> +                return 0; /* execute-only code segment */
>              break;
>          case hvm_access_write:
>              if ( (reg->attr.fields.type & 0xa) != 0x2 )
> -                goto gpf; /* not a writable data segment */
> +                return 0; /* not a writable data segment */
>              break;
>          default:
>              break;
>          }
>  
> -        last_byte = offset + bytes - 1;
> +        last_byte = (uint32_t)offset + bytes - 1;
>  
>          /* Is this a grows-down data segment? Special limit check if so. */
>          if ( (reg->attr.fields.type & 0xc) == 0x4 )
> @@ -1973,10 +1975,10 @@ int hvm_virtual_to_linear_addr(
>  
>              /* Check first byte and last byte against respective bounds. */
>              if ( (offset <= reg->limit) || (last_byte < offset) )
> -                goto gpf;
> +                return 0;
>          }
>          else if ( (last_byte > reg->limit) || (last_byte < offset) )
> -            goto gpf; /* last byte is beyond limit or wraps 0xFFFFFFFF */
> +            return 0; /* last byte is beyond limit or wraps 0xFFFFFFFF */
>  
>          /*
>           * Hardware truncates to 32 bits in compatibility mode.
> @@ -1993,15 +1995,14 @@ int hvm_virtual_to_linear_addr(
>          if ( (seg == x86_seg_fs) || (seg == x86_seg_gs) )
>              addr += reg->base;
>  
> -        if ( !is_canonical_address(addr) )
> -            goto gpf;
> +        last_byte = addr + bytes - 1;
> +        if ( !is_canonical_address(addr) || last_byte < addr ||
> +             !is_canonical_address(last_byte) )
> +            return 0;
>      }
>  
>      *linear_addr = addr;
>      return 1;
> -
> - gpf:
> -    return 0;
>  }
>  
>  /* On non-NULL return, we leave this function holding an additional
> 
> 
> 



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