Re: [Qemu-devel] [PATCH v2] mips: Decide to map PAGE_EXEC in map_address

[Philippe Mathieu-Daudé]

Hi Jakub,

On 5/16/19 3:10 PM, Jakub Jermar wrote:
> Hi,
> 
> On 5/3/19 12:02 PM, Jakub Jermar wrote:
>> Hi,
>>
>> On 4/23/19 4:58 PM, Jakub Jermar wrote:
>>> Hi Philippe!
>>>
>>> On 4/23/19 3:48 PM, Philippe Mathieu-Daudé wrote:
>>>> Hi Jakub,
>>>>
>>>> On 4/23/19 1:00 PM, Jakub Jermář wrote:
>>>>> This commit addresses QEMU Bug #1825311:
>>>>>
>>>>>   mips_cpu_handle_mmu_fault renders all accessed pages executable
>>>>>
>>>>> It allows finer-grained control over whether the accessed page should be
>>>>> executable by moving the decision to the underlying map_address
>>>>> function, which has more information for this.
>>>>>
>>>>> As a result, pages that have the XI bit set in the TLB and are accessed
>>>>> for read/write, don't suddenly end up being executable.
>>>>>
>>>>
>>>> Fixes: https://bugs.launchpad.net/qemu/+bug/1825311
>>>>
>>>>> Signed-off-by: Jakub Jermář <address@hidden>
>>>>> ---
>>>>>  target/mips/helper.c | 17 ++++++++++-------
>>>>>  1 file changed, 10 insertions(+), 7 deletions(-)
>>>>>
>>>>> diff --git a/target/mips/helper.c b/target/mips/helper.c
>>>>> index c44cdca3b5..132d073fbe 100644
>>>>> --- a/target/mips/helper.c
>>>>> +++ b/target/mips/helper.c
>>>>> @@ -43,7 +43,7 @@ int no_mmu_map_address (CPUMIPSState *env, hwaddr 
>>>>> *physical, int *prot,
>>>>>                          target_ulong address, int rw, int access_type)
>>>>>  {
>>>>>      *physical = address;
>>>>> -    *prot = PAGE_READ | PAGE_WRITE;
>>>>> +    *prot = PAGE_READ | PAGE_WRITE | PAGE_EXEC;
>>>>>      return TLBRET_MATCH;
>>>>>  }
>>>>>  
>>>>> @@ -61,7 +61,7 @@ int fixed_mmu_map_address (CPUMIPSState *env, hwaddr 
>>>>> *physical, int *prot,
>>>>>      else
>>>>>          *physical = address;
>>>>>  
>>>>> -    *prot = PAGE_READ | PAGE_WRITE;
>>>>> +    *prot = PAGE_READ | PAGE_WRITE | PAGE_EXEC;
>>>>>      return TLBRET_MATCH;
>>>>>  }
>>>>>  
>>>>> @@ -101,6 +101,9 @@ int r4k_map_address (CPUMIPSState *env, hwaddr 
>>>>> *physical, int *prot,
>>>>>                  *prot = PAGE_READ;
>>>>>                  if (n ? tlb->D1 : tlb->D0)
>>>>>                      *prot |= PAGE_WRITE;
>>>>> +                if (!(n ? tlb->XI1 : tlb->XI0)) {
>>>>> +                    *prot |= PAGE_EXEC;
>>>>> +                }
>>>>
>>>> This was indeed missed in commit 2fb58b73746e.

Aleksandar, if this patch is OK with you, can you amend this comment,
and add the "Fixes:" tag too when applying? Thanks!

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

>>>>
>>>>>                  return TLBRET_MATCH;
>>>>>              }
>>>>>              return TLBRET_DIRTY;
>>>>> @@ -182,7 +185,7 @@ static int get_seg_physical_address(CPUMIPSState 
>>>>> *env, hwaddr *physical,
>>>>>      } else {
>>>>>          /* The segment is unmapped */
>>>>>          *physical = physical_base | (real_address & segmask);
>>>>> -        *prot = PAGE_READ | PAGE_WRITE;
>>>>> +        *prot = PAGE_READ | PAGE_WRITE | PAGE_EXEC;
>>>>>          return TLBRET_MATCH;
>>>>>      }
>>>>>  }
>>>>> @@ -913,8 +916,8 @@ int mips_cpu_handle_mmu_fault(CPUState *cs, vaddr 
>>>>> address, int size, int rw,
>>>>>      }
>>>>>      if (ret == TLBRET_MATCH) {
>>>>>          tlb_set_page(cs, address & TARGET_PAGE_MASK,
>>>>> -                     physical & TARGET_PAGE_MASK, prot | PAGE_EXEC,
>>>>> -                     mmu_idx, TARGET_PAGE_SIZE);
>>>>> +                     physical & TARGET_PAGE_MASK, prot, mmu_idx,
>>>>> +                     TARGET_PAGE_SIZE);
>>>>>          ret = 0;
>>>>>      } else if (ret < 0)
>>>>>  #endif
>>>>> @@ -936,8 +939,8 @@ int mips_cpu_handle_mmu_fault(CPUState *cs, vaddr 
>>>>> address, int size, int rw,
>>>>>                                             address, rw, access_type, 
>>>>> mmu_idx);
>>>>>                  if (ret == TLBRET_MATCH) {
>>>>>                      tlb_set_page(cs, address & TARGET_PAGE_MASK,
>>>>> -                            physical & TARGET_PAGE_MASK, prot | 
>>>>> PAGE_EXEC,
>>>>> -                            mmu_idx, TARGET_PAGE_SIZE);
>>>>> +                            physical & TARGET_PAGE_MASK, prot, mmu_idx,
>>>>> +                            TARGET_PAGE_SIZE);
>>>>>                      ret = 0;
>>>>>                      return ret;
>>>>>                  }
>>>>>
>>>>
>>>> Your patch looks correct, but I'd like to test it.
>>>> Do you have a reproducer?
>>>> Can you describe the command line you used?
>>>
>>> I've just attached a reproducer image and script to the bug. It's a
>>> 32-bit little-endian test binary running on top of the L4Re microkernel.

I can't get the "TAP" output you described on launchpad.

>>> Let me know if you also need a 64-bit version.

64-bit version is welcomed.

>>> I tested both 32 and 64-bit versions of the reproducer and also checked
>>> to see that the the other images I have lying around here (Linux 2.6.32
>>> big endian and HelenOS master little-endian, both 32-bit for 4Kc)
>>> continue to run without regressions.

Yes, definitively an improvement:
Tested-by: Philippe Mathieu-Daudé <address@hidden>

Regards,

Phil.