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

[Jakub Jermar <jakub.jermar@kernkonzept.com>]

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 <jakub.jermar@kernkonzept.com>
>>>> ---
>>>>  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.
>>>
>>>>                  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.
>> Let me know if you also need a 64-bit version.
>>
>> 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.
>>
>> Best regards,
>> Jakub
> 
> (ping)
> 
> Is there anything else I can do to help to get this merged?
> 
> https://patchew.org/QEMU/20190423110034.1260142-1-jakub.jermar@kernkonzept.com/

Has anyone managed to have a look at this?

Thanks,
Jakub

> 
> Thanks,
> Jakub
> 

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