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

[Luiz Capitulino <lcapitulino@redhat.com>]

On Thu, 30 May 2013 15:16:18 +0200
Laszlo Ersek <lersek@redhat.com> wrote:

> On 05/30/13 14:59, Luiz Capitulino wrote:
> > 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...
> 
> I didn't miss your submission and did find it OK, I just felt unsure
> about stating so, because "simple" patches like this are prime territory
> to burn someone's R-b's worth (ie. to expose a reviewer's lack of
> information / experience). But hey, what can I lose? The patch does look
> good to me, so

Thank you Laszlo! It's also new territory for me, that's why I'm asking
for reviews (otherwise I'd just sneak it in some pull request :-)

> 
> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
> 
> > 
> >> ---
> >>
> >> 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
> > 
> > 
>