Re: [Qemu-devel] [PATCH] walk_pml4e(): fix abort on bad PML4E/PDPTE/PDE/PTE addresses

[Luiz Capitulino <lcapitulino@redhat.com>]

On Tue, 28 May 2013 14:19:22 -0400
Luiz Capitulino <lcapitulino@redhat.com> wrote:

> The code used to walk IA-32e page-tables, and possibly PAE page-tables,
> uses the bit mask ~0xfff to get the next PML4E/PDPTE/PDE/PTE address.
> 
> However, as we use a uint64_t to store the resulting address, that mask
> gets expanded to 0xfffffffffffff000 which not only ends up selecting
> reserved bits but also selects the XD bit (execute-disable) which
> happens to be enabled by Windows 8, causing qemu_get_ram_ptr() to abort.
> 
> This commit fixes that problem by replacing ~0xfff by a correct mask
> that only selects the address bit range (ie. bits 51:12).
> 
> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

Ping? Wen?

Would be nice get a Reviewed-by before merging...

> ---
> 
> PS: I (obviously) don't any more core dumps with this patch applied, but
>     I couldn't check if the Windows dump is correct (does anyone know
>     how to do this?). I did quickly check on Linux though.
> 
>  target-i386/arch_memory_mapping.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/target-i386/arch_memory_mapping.c b/target-i386/arch_memory_mapping.c
> index 844893f..24884bd 100644
> --- a/target-i386/arch_memory_mapping.c
> +++ b/target-i386/arch_memory_mapping.c
> @@ -75,6 +75,8 @@ static void walk_pte2(MemoryMappingList *list,
>  }
>  
>  /* PAE Paging or IA-32e Paging */
> +#define PLM4_ADDR_MASK 0xffffffffff000 /* selects bits 51:12 */
> +
>  static void walk_pde(MemoryMappingList *list, hwaddr pde_start_addr,
>                       int32_t a20_mask, target_ulong start_line_addr)
>  {
> @@ -105,7 +107,7 @@ static void walk_pde(MemoryMappingList *list, hwaddr pde_start_addr,
>              continue;
>          }
>  
> -        pte_start_addr = (pde & ~0xfff) & a20_mask;
> +        pte_start_addr = (pde & PLM4_ADDR_MASK) & a20_mask;
>          walk_pte(list, pte_start_addr, a20_mask, line_addr);
>      }
>  }
> @@ -208,7 +210,7 @@ static void walk_pdpe(MemoryMappingList *list,
>              continue;
>          }
>  
> -        pde_start_addr = (pdpe & ~0xfff) & a20_mask;
> +        pde_start_addr = (pdpe & PLM4_ADDR_MASK) & a20_mask;
>          walk_pde(list, pde_start_addr, a20_mask, line_addr);
>      }
>  }
> @@ -231,7 +233,7 @@ static void walk_pml4e(MemoryMappingList *list,
>          }
>  
>          line_addr = ((i & 0x1ffULL) << 39) | (0xffffULL << 48);
> -        pdpe_start_addr = (pml4e & ~0xfff) & a20_mask;
> +        pdpe_start_addr = (pml4e & PLM4_ADDR_MASK) & a20_mask;
>          walk_pdpe(list, pdpe_start_addr, a20_mask, line_addr);
>      }
>  }
> @@ -249,7 +251,7 @@ int cpu_get_memory_mapping(MemoryMappingList *list, CPUArchState *env)
>          if (env->hflags & HF_LMA_MASK) {
>              hwaddr pml4e_addr;
>  
> -            pml4e_addr = (env->cr[3] & ~0xfff) & env->a20_mask;
> +            pml4e_addr = (env->cr[3] & PLM4_ADDR_MASK) & env->a20_mask;
>              walk_pml4e(list, pml4e_addr, env->a20_mask);
>          } else
>  #endif