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llvm-project/lldb/source/Plugins/Process/Utility/LinuxSignals.cpp
David Spickett 7dbfc2bd00
[lldb][AArch64][Linux] Add support for the Permission Overlay Extension (POE) (#177145) 
This change adds initial support for managing the Permission Overlay
Extension (POE). This extension allows userspace programs to change
memory permissions without making a sycall.

This is used to implement Linux's memory protection keys
(https://docs.kernel.org/core-api/protection-keys.html) on AArch64.

Overview of POE:
* Page table entries have a set of permissions. To change these, a
program would have to use a syscall which adds overhead.
* 3 bits of the page table entry are used for a protection key 0-7.
* POE adds a new register "por" (POR_EL0 in the manual) which stores
4-bit sets of permissions.
* The protection key is an index into this por register.
* Permissions in POR are applied on top of the page table permissions,
but may only remove permissions. For example, if you overlay
read/execute over read/write, the result is read. Since execute was not
in the page table permissions.
* This register can be modified without leaving userspace, making
permission changes faster.

To help debug this, I have made the following changes to LLDB:
* Ability to read and write the por register.
* Save and restore of por when running expressions.
* Register field definitions to print the por permissions in a human
readable form.
* Recognition of memory protection key faults as a distinct type of
SIGSEGV (this will apply to Linux on any architecture).

There are a few more features to add around memory region information,
that will be in follow up changes. As will documentation and release
notes for all the POE features.
2026-02-19 10:25:31 +00:00

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//===-- LinuxSignals.cpp --------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "LinuxSignals.h"
// mips-linux debugging is not supported and mips uses different numbers for
// some signals (e.g. SIGBUS) on linux, so we skip the static checks below. The
// definitions here can be used for debugging non-mips targets on a mips-hosted
// lldb.
#if defined(__linux__) && !defined(__mips__)
#include <csignal>
#ifndef SEGV_BNDERR
#define SEGV_BNDERR 3
#endif
#ifndef SEGV_MTEAERR
#define SEGV_MTEAERR 8
#endif
#ifndef SEGV_MTESERR
#define SEGV_MTESERR 9
#endif
#ifndef SEGV_CPERR
#define SEGV_CPERR 10
#endif
#ifndef SI_QUEUE
#define SI_QUEUE -1
#endif
#ifndef SI_TIMER
#define SI_TIMER -2
#endif
#ifndef SI_MESGQ
#define SI_MESGQ -3
#endif
#ifndef SI_ASYNCIO
#define SI_ASYNCIO -4
#endif
#ifndef SI_SIGIO
#define SI_SIGIO -5
#endif
#ifndef SI_TKILL
#define SI_TKILL -6
#endif
#ifndef SI_DETHREAD
#define SI_DETHREAD -7
#endif
#ifndef SI_ASYNCNL
#define SI_ASYNCNL -60
#endif
#define ADD_SIGCODE(signal_name, signal_value, code_name, code_value, ...) \
static_assert(signal_name == signal_value, \
"Value mismatch for signal number " #signal_name); \
static_assert(code_name == code_value, \
"Value mismatch for signal code " #code_name); \
AddSignalCode(signal_value, code_value, __VA_ARGS__)
#else
#define ADD_SIGCODE(signal_name, signal_value, code_name, code_value, ...) \
AddSignalCode(signal_value, code_value, __VA_ARGS__)
#endif /* if defined(__linux__) && !defined(__mips__) */
// See siginfo.h in the Linux Kernel, these codes can be sent for any signal.
#define ADD_LINUX_SIGNAL(signo, name, ...) \
AddSignal(signo, name, __VA_ARGS__); \
ADD_SIGCODE(signo, signo, SI_USER, 0, "sent by kill, sigsend or raise", \
SignalCodePrintOption::Sender); \
ADD_SIGCODE(signo, signo, SI_KERNEL, 0x80, "sent by kernel (SI_KERNEL)", \
SignalCodePrintOption::Sender); \
ADD_SIGCODE(signo, signo, SI_QUEUE, -1, "sent by sigqueue", \
SignalCodePrintOption::Sender); \
ADD_SIGCODE(signo, signo, SI_TIMER, -2, "sent by timer expiration", \
SignalCodePrintOption::Sender); \
ADD_SIGCODE(signo, signo, SI_MESGQ, -3, \
"sent by real time mesq state change", \
SignalCodePrintOption::Sender); \
ADD_SIGCODE(signo, signo, SI_ASYNCIO, -4, "sent by AIO completion", \
SignalCodePrintOption::Sender); \
ADD_SIGCODE(signo, signo, SI_SIGIO, -5, "sent by queued SIGIO", \
SignalCodePrintOption::Sender); \
ADD_SIGCODE(signo, signo, SI_TKILL, -6, "sent by tkill system call", \
SignalCodePrintOption::Sender); \
ADD_SIGCODE(signo, signo, SI_DETHREAD, -7, \
"sent by execve() killing subsidiary threads", \
SignalCodePrintOption::Sender); \
ADD_SIGCODE(signo, signo, SI_ASYNCNL, -60, \
"sent by glibc async name lookup completion", \
SignalCodePrintOption::Sender);
using namespace lldb_private;
LinuxSignals::LinuxSignals() : UnixSignals() { Reset(); }
void LinuxSignals::Reset() {
m_signals.clear();
// clang-format off
// SIGNO NAME SUPPRESS STOP NOTIFY DESCRIPTION
// ====== ============== ======== ====== ====== ===================================================
ADD_LINUX_SIGNAL(1, "SIGHUP", false, true, true, "hangup");
ADD_LINUX_SIGNAL(2, "SIGINT", true, true, true, "interrupt");
ADD_LINUX_SIGNAL(3, "SIGQUIT", false, true, true, "quit");
ADD_LINUX_SIGNAL(4, "SIGILL", false, true, true, "illegal instruction");
ADD_SIGCODE(SIGILL, 4, ILL_ILLOPC, 1, "illegal opcode");
ADD_SIGCODE(SIGILL, 4, ILL_ILLOPN, 2, "illegal operand");
ADD_SIGCODE(SIGILL, 4, ILL_ILLADR, 3, "illegal addressing mode");
ADD_SIGCODE(SIGILL, 4, ILL_ILLTRP, 4, "illegal trap");
ADD_SIGCODE(SIGILL, 4, ILL_PRVOPC, 5, "privileged opcode");
ADD_SIGCODE(SIGILL, 4, ILL_PRVREG, 6, "privileged register");
ADD_SIGCODE(SIGILL, 4, ILL_COPROC, 7, "coprocessor error");
ADD_SIGCODE(SIGILL, 4, ILL_BADSTK, 8, "internal stack error");
ADD_LINUX_SIGNAL(5, "SIGTRAP", true, true, true, "trace trap (not reset when caught)");
ADD_LINUX_SIGNAL(6, "SIGABRT", false, true, true, "abort()/IOT trap", "SIGIOT");
ADD_LINUX_SIGNAL(7, "SIGBUS", false, true, true, "bus error");
ADD_SIGCODE(SIGBUS, 7, BUS_ADRALN, 1, "illegal alignment");
ADD_SIGCODE(SIGBUS, 7, BUS_ADRERR, 2, "illegal address");
ADD_SIGCODE(SIGBUS, 7, BUS_OBJERR, 3, "hardware error");
ADD_LINUX_SIGNAL(8, "SIGFPE", false, true, true, "floating point exception");
ADD_SIGCODE(SIGFPE, 8, FPE_INTDIV, 1, "integer divide by zero");
ADD_SIGCODE(SIGFPE, 8, FPE_INTOVF, 2, "integer overflow");
ADD_SIGCODE(SIGFPE, 8, FPE_FLTDIV, 3, "floating point divide by zero");
ADD_SIGCODE(SIGFPE, 8, FPE_FLTOVF, 4, "floating point overflow");
ADD_SIGCODE(SIGFPE, 8, FPE_FLTUND, 5, "floating point underflow");
ADD_SIGCODE(SIGFPE, 8, FPE_FLTRES, 6, "floating point inexact result");
ADD_SIGCODE(SIGFPE, 8, FPE_FLTINV, 7, "floating point invalid operation");
ADD_SIGCODE(SIGFPE, 8, FPE_FLTSUB, 8, "subscript out of range");
ADD_LINUX_SIGNAL(9, "SIGKILL", false, true, true, "kill");
ADD_LINUX_SIGNAL(10, "SIGUSR1", false, true, true, "user defined signal 1");
ADD_LINUX_SIGNAL(11, "SIGSEGV", false, true, true, "segmentation violation");
ADD_SIGCODE(SIGSEGV, 11, SEGV_MAPERR, 1, "address not mapped to object", SignalCodePrintOption::Address);
ADD_SIGCODE(SIGSEGV, 11, SEGV_ACCERR, 2, "invalid permissions for mapped object", SignalCodePrintOption::Address);
ADD_SIGCODE(SIGSEGV, 11, SEGV_BNDERR, 3, "failed address bounds checks", SignalCodePrintOption::Bounds);
ADD_SIGCODE(SIGSEGV, 11, SEGV_PKUERR, 4, "failed protection key checks", SignalCodePrintOption::Address);
ADD_SIGCODE(SIGSEGV, 11, SEGV_MTEAERR, 8, "async tag check fault");
ADD_SIGCODE(SIGSEGV, 11, SEGV_MTESERR, 9, "sync tag check fault", SignalCodePrintOption::Address);
ADD_SIGCODE(SIGSEGV, 11, SEGV_CPERR, 10, "control protection fault");
// Some platforms will occasionally send nonstandard spurious SI_KERNEL
// codes. One way to get this is via unaligned SIMD loads. Treat it as invalid address.
ADD_SIGCODE(SIGSEGV, 11, SI_KERNEL, 0x80, "invalid address", SignalCodePrintOption::Address);
ADD_LINUX_SIGNAL(12, "SIGUSR2", false, true, true, "user defined signal 2");
ADD_LINUX_SIGNAL(13, "SIGPIPE", false, true, true, "write to pipe with reading end closed");
ADD_LINUX_SIGNAL(14, "SIGALRM", false, false, false, "alarm");
ADD_LINUX_SIGNAL(15, "SIGTERM", false, true, true, "termination requested");
ADD_LINUX_SIGNAL(16, "SIGSTKFLT", false, true, true, "stack fault");
ADD_LINUX_SIGNAL(17, "SIGCHLD", false, false, true, "child status has changed", "SIGCLD");
ADD_LINUX_SIGNAL(18, "SIGCONT", false, false, true, "process continue");
ADD_LINUX_SIGNAL(19, "SIGSTOP", true, true, true, "process stop");
ADD_LINUX_SIGNAL(20, "SIGTSTP", false, true, true, "tty stop");
ADD_LINUX_SIGNAL(21, "SIGTTIN", false, true, true, "background tty read");
ADD_LINUX_SIGNAL(22, "SIGTTOU", false, true, true, "background tty write");
ADD_LINUX_SIGNAL(23, "SIGURG", false, true, true, "urgent data on socket");
ADD_LINUX_SIGNAL(24, "SIGXCPU", false, true, true, "CPU resource exceeded");
ADD_LINUX_SIGNAL(25, "SIGXFSZ", false, true, true, "file size limit exceeded");
ADD_LINUX_SIGNAL(26, "SIGVTALRM", false, true, true, "virtual time alarm");
ADD_LINUX_SIGNAL(27, "SIGPROF", false, false, false, "profiling time alarm");
ADD_LINUX_SIGNAL(28, "SIGWINCH", false, false, false, "window size changes");
ADD_LINUX_SIGNAL(29, "SIGIO", false, true, true, "input/output ready/Pollable event", "SIGPOLL");
ADD_LINUX_SIGNAL(30, "SIGPWR", false, true, true, "power failure");
ADD_LINUX_SIGNAL(31, "SIGSYS", false, true, true, "invalid system call");
ADD_LINUX_SIGNAL(32, "SIG32", false, false, false, "threading library internal signal 1");
ADD_LINUX_SIGNAL(33, "SIG33", false, false, false, "threading library internal signal 2");
ADD_LINUX_SIGNAL(34, "SIGRTMIN", false, false, false, "real time signal 0");
ADD_LINUX_SIGNAL(35, "SIGRTMIN+1", false, false, false, "real time signal 1");
ADD_LINUX_SIGNAL(36, "SIGRTMIN+2", false, false, false, "real time signal 2");
ADD_LINUX_SIGNAL(37, "SIGRTMIN+3", false, false, false, "real time signal 3");
ADD_LINUX_SIGNAL(38, "SIGRTMIN+4", false, false, false, "real time signal 4");
ADD_LINUX_SIGNAL(39, "SIGRTMIN+5", false, false, false, "real time signal 5");
ADD_LINUX_SIGNAL(40, "SIGRTMIN+6", false, false, false, "real time signal 6");
ADD_LINUX_SIGNAL(41, "SIGRTMIN+7", false, false, false, "real time signal 7");
ADD_LINUX_SIGNAL(42, "SIGRTMIN+8", false, false, false, "real time signal 8");
ADD_LINUX_SIGNAL(43, "SIGRTMIN+9", false, false, false, "real time signal 9");
ADD_LINUX_SIGNAL(44, "SIGRTMIN+10", false, false, false, "real time signal 10");
ADD_LINUX_SIGNAL(45, "SIGRTMIN+11", false, false, false, "real time signal 11");
ADD_LINUX_SIGNAL(46, "SIGRTMIN+12", false, false, false, "real time signal 12");
ADD_LINUX_SIGNAL(47, "SIGRTMIN+13", false, false, false, "real time signal 13");
ADD_LINUX_SIGNAL(48, "SIGRTMIN+14", false, false, false, "real time signal 14");
ADD_LINUX_SIGNAL(49, "SIGRTMIN+15", false, false, false, "real time signal 15");
ADD_LINUX_SIGNAL(50, "SIGRTMAX-14", false, false, false, "real time signal 16"); // switching to SIGRTMAX-xxx to match "kill -l" output
ADD_LINUX_SIGNAL(51, "SIGRTMAX-13", false, false, false, "real time signal 17");
ADD_LINUX_SIGNAL(52, "SIGRTMAX-12", false, false, false, "real time signal 18");
ADD_LINUX_SIGNAL(53, "SIGRTMAX-11", false, false, false, "real time signal 19");
ADD_LINUX_SIGNAL(54, "SIGRTMAX-10", false, false, false, "real time signal 20");
ADD_LINUX_SIGNAL(55, "SIGRTMAX-9", false, false, false, "real time signal 21");
ADD_LINUX_SIGNAL(56, "SIGRTMAX-8", false, false, false, "real time signal 22");
ADD_LINUX_SIGNAL(57, "SIGRTMAX-7", false, false, false, "real time signal 23");
ADD_LINUX_SIGNAL(58, "SIGRTMAX-6", false, false, false, "real time signal 24");
ADD_LINUX_SIGNAL(59, "SIGRTMAX-5", false, false, false, "real time signal 25");
ADD_LINUX_SIGNAL(60, "SIGRTMAX-4", false, false, false, "real time signal 26");
ADD_LINUX_SIGNAL(61, "SIGRTMAX-3", false, false, false, "real time signal 27");
ADD_LINUX_SIGNAL(62, "SIGRTMAX-2", false, false, false, "real time signal 28");
ADD_LINUX_SIGNAL(63, "SIGRTMAX-1", false, false, false, "real time signal 29");
ADD_LINUX_SIGNAL(64, "SIGRTMAX", false, false, false, "real time signal 30");
// clang-format on
}
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