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

[Jakub Jermar]

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.
> 
>>                  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

> 
> Thanks,
> 
> Phil.
> 

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