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VirtualMachine: disable NaCl platform qualification to run armhf nexe on Raspberry Pi 4 #740

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illwieckz merged 1 commit into from
Nov 17, 2022
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VirtualMachine: disable NaCl platform qualification to run armhf nexe on Raspberry Pi 4 #740

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19 changes: 19 additions & 0 deletions src/engine/framework/VirtualMachine.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -256,6 +256,25 @@ std::pair<Sys::OSHandle, IPC::Socket> CreateNaClVM(std::pair<IPC::Socket, IPC::S
args.push_back(nacl_loader.c_str());
args.push_back("--r_debug=0xXXXXXXXXXXXXXXXX");
args.push_back("--reserved_at_zero=0xXXXXXXXXXXXXXXXX");

#if defined(DAEMON_ARCH_armhf)
/* This is required to run on Raspberry Pi 4,
otherwise nexe loading fails with this message:

Error while loading "sgame-armhf.nexe": CPU model is not supported

From nacl_loader --help we can read:

-Q disable platform qualification (dangerous!)

When this option is enabled, nacl_loader will print:

PLATFORM QUALIFICATION DISABLED BY -Q - Native Client's sandbox will be unreliable!

But the nexe will load and run. */

args.push_back("-Q");

@necessarily-equal necessarily-equal Nov 17, 2022

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According to https://github.com/mseaborn/nacl-wiki/blob/master/PlatformQualification.wiki#architecture-specific-checks-arm, here's what this checks:

Architecture-specific checks: ARM

ARMv7-A or later

We require a minimum architecture of ARMv7-A.

  • Rationale:* ARMv7 adds instructions that are important for PNaCl (64-bit load/store exclusive), clearly defines the CPUID mechanism, and includes the operations from ARMv6T2 that we require for correctness.
  • May change:* across a reboot. Unlikely to change under virtualization.
  • Method:* we use an assembly sequence, suggested by ARM Ltd, to verify architecture revision.

DEP present and working

Data Execution Prevention (DEP) must be enabled and functional.

  • Rationale:* The ARM sandbox allows the code-data boundary to fall at any page. Thus jumps to non-validated data are trivial. We require DEP to prevent this. Even on processors that support XN (all supported ARM processors), this can be disabled by the operating system.
  • May change:* across a reboot on real hardware. Under virtualization this can change even while the process runs.
  • Method:* we generate functions in heap and stack memory and execute them. We verify that we take the expected exception.

OS-specific checks: Linux

SysV SHM

SysV SHM must be supported and pass certain feature tests, including interacting predictably with mmap (see src/trusted/platform_qualify/linux/sysv_shm_and_mmap.c).

  • Rationale:* unclear
  • May change:* with kernel upgrades. (Note that with Ksplice this does not imply a reboot necessarily, though Ksplice currently isn't capable of this sort of change.)
  • Method:* See source implementation.

I don't know what check fails, but I think it's "not that bad" to disable this for now.

LGTM

@illwieckz illwieckz Nov 17, 2022 •
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Yes, the RPI4 uses armv8-a and I also verified the fact XN works, so I don't know why the qualification fails.

Also even the naclsdk disables qualification when running nexe over emulated qualified arm cpu on qemu in their scripts…

#endif
#else
Q_UNUSED(bootstrap);
args.push_back(nacl_loader.c_str());
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