[Qemu-devel] [Bug 1825311] Re: mips_cpu_handle_mmu_fault renders all accessed pages executable

[Jakub Jermar]

I am attaching a reproducer image and script.

Unpatched execution ends like this:

...
TAP TEST START
1..2
not ok 1 NonExecutable::ElfDataIsNotExecutable
# Assertion failed 
/home/jermar/Kernkonzept/software/l4/pkg/l4re-core/test/moe/test_nx.cc:103
# Expected: -(L4_EIPC_LO + l4_ipc_error(tag, l4_utcb())) >= 0
# Actual: -2003 (Receive timeout)
# There was no IPC error.
# Assertion failed 
/home/jermar/Kernkonzept/software/l4/pkg/l4re-core/test/moe/test_nx.cc:125
# Expected equality of these values:
#   pfa
#     Which is: 360
#   (l4_addr_t)execute_data
#     Which is: 17633344
# The page fault occured at the expected location.
not ok 2 NonExecutable::StackIsNotExecutable
# Assertion failed 
/home/jermar/Kernkonzept/software/l4/pkg/l4re-core/test/moe/test_nx.cc:103
# Expected: -(L4_EIPC_LO + l4_ipc_error(tag, l4_utcb())) >= 0
# Actual: -2003 (Receive timeout)
# There was no IPC error.
# Assertion failed 
/home/jermar/Kernkonzept/software/l4/pkg/l4re-core/test/moe/test_nx.cc:144
# Expected equality of these values:
#   pfa
#     Which is: 4358144
#   stack_func
#     Which is: 4276000
# The page fault occured at the expected location.
TAP TEST FINISHED


With the proposed patch applied, the execution should end with something
like this:

...
TAP TEST START
1..2
ok 1 NonExecutable::ElfDataIsNotExecutable
ok 2 NonExecutable::StackIsNotExecutable
TAP TEST FINISHED


** Attachment added: "Image and script for reproducing this bug."
   
https://bugs.launchpad.net/qemu/+bug/1825311/+attachment/5258264/+files/reproducer.tar.xz

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https://bugs.launchpad.net/bugs/1825311

Title:
  mips_cpu_handle_mmu_fault renders all accessed pages executable

Status in QEMU:
  New

Bug description:
  On MIPS, data accesses to pages mapped in the TLB result in
  mips_cpu_handle_mmu_fault() marking the page unconditionally
  executable, even if the TLB entry has the XI bit set. Later on, when
  there is an attempt to execute this page, no exception is generated,
  even though TLBXI is expected.

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