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Disable ptrace on arm64e running iOS 14.2 and greater #22377

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Disable ptrace on arm64e running iOS 14.2 and greater #22377

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59 changes: 59 additions & 0 deletions runtime/ptrace_check.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,7 @@
#include <sys/sysctl.h>
#include <sys/types.h>

#include <mach/machine.h>
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Should this be conditionally imported and used? @chinmaygarde might have a better idea of whether this is available on all our target platforms.

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This is fine. TRACING_CHECKS_NECESSARY is unset on all other platforms.

#include <mutex>

#include "flutter/fml/build_config.h"
Expand Down Expand Up @@ -114,7 +115,65 @@ static bool EnableTracingManually(const Settings& vm_settings) {
return true;
}

static bool IsTracingCheckUnnecessaryOnVersion() {
#if !OS_IOS || TARGET_OS_SIMULATOR
return true;
#endif

// Check for arm64e.
cpu_type_t cputype = 0;
size_t cputype_size = sizeof(cpu_type_t);
if (::sysctlbyname("hw.cputype", &cputype, &cputype_size, nullptr, 0) < 0) {
FML_LOG(ERROR) << "Could not execute sysctl() to get CPU type: "
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Here and elsewhere: Early return in case of error.

<< strerror(errno);
}

cpu_subtype_t cpusubtype = 0;
if (::sysctlbyname("hw.cpusubtype", &cpusubtype, &cputype_size, nullptr, 0) <
0) {
FML_LOG(ERROR) << "Could not execute sysctl() to get CPU subtype: "
<< strerror(errno);
}

// Tracing is necessary unless the device is arm64e (A12 chip or higher).
if (cputype != CPU_TYPE_ARM64 || cpusubtype != CPU_SUBTYPE_ARM64E) {
return false;
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ultra-nit: there's a triple negation at this point :) false to != arm64 to unnecessary. Can we simplify slightly?

}

// Check for iOS 14.2 and higher.
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up to you but it feels like we're building in a lot of platform specific knowledge at this point. How about just letting this file statically take a SetOSVersionMayNeedTracingCheck injection or something and FlutterEngine can just set it to https://developer.apple.com/documentation/foundation/nsprocessinfo/1414876-isoperatingsystematleastversion? Could save us some work.

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@jmagman jmagman Nov 9, 2020 •
edited
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If this were all in obj-c++ world then I wouldn't have bothered with all these syctl checks. But it would need to be injected from:

engine/runtime/dart_vm.cc

Line 333 in e78e405

const bool tracing_result = EnableTracingIfNecessary(settings_);

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that's what I meant injecting it statically (since all these stuff is static anyway). Since the engine calls first, we know it would be set before dart calls it again.

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I don't love that the lower level code would require a static variable to be set before it can be called, without enforcing that ordering itself. Seems like an easy opportunity for bugs if this ever gets refactored. Will defer to @chinmaygarde's opinion here.

If we decide to keep this kern.osversion parsing I'll add a unit test.

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I love the initiative in doing this in C, but let's make this an ObjC++ TU and use NSOperatingSystemVersion instead. You can remove the TRACING_CHECKS_NECESSARY macro and add a stub C++ file for non-Darwin platforms.

size_t osversion_size;
::sysctlbyname("kern.osversion", NULL, &osversion_size, NULL, 0);
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Unchecked error code. Though, I'd suggest using the ObjC++ variant instead.

char osversionBuffer[osversion_size];

if (::sysctlbyname("kern.osversion", osversionBuffer, &osversion_size, NULL,
0) < 0) {
FML_LOG(ERROR) << "Could not execute sysctl() to get current OS version: "
<< strerror(errno);

return false;
}

int major_version = 0;
char minor_letter = 'Z';

for (size_t index = 0; index < osversion_size; index++) {
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This parsing felt like an interview question (atoi!), happy to try something more idiomatic if ya'll can think of a better way to do it. I started with an istringstream but it actually wound up being identical logic so it didn't seem worth the extra object.

char version_char = osversionBuffer[index];
// Find the minor version build letter.
if (isalpha(version_char)) {
major_version = atoi((const char*)osversionBuffer);
minor_letter = toupper(version_char);
break;
}
}
// 18B92 is iOS 14.2 beta release candidate where tracing became unnecessary.
return major_version > 18 || (major_version == 18 && minor_letter >= 'B');
}

static bool EnableTracingIfNecessaryOnce(const Settings& vm_settings) {
if (IsTracingCheckUnnecessaryOnVersion()) {
return true;
}

if (IsLaunchedByFlutterCLI(vm_settings)) {
return true;
}
Expand Down