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At the moment GDB only handles pointer authentication (pauth) for userspace addresses and if we're debugging a Linux-hosted program. The Linux Kernel can be configured to use pauth instructions for some additional security hardening, but GDB doesn't handle this well. To overcome this limitation, GDB needs a couple things: 1 - The target needs to advertise pauth support. 2 - The hook to remove non-address bits from a pointer needs to be registered in aarch64-tdep.c as opposed to aarch64-linux-tdep.c. There is a patch for QEMU that addresses the first point, and it makes QEMU's gdbstub expose a couple more pauth mask registers, so overall we will have up to 4 pauth masks (2 masks or 4 masks): pauth_dmask pauth_cmask pauth_dmask_high pauth_cmask_high pauth_dmask and pauth_cmask are the masks used to remove pauth signatures from userspace addresses. pauth_dmask_high and pauth_cmask_high masks are used to remove pauth signatures from kernel addresses. The second point is easily addressed by moving code around. When debugging a Linux Kernel built with pauth with an unpatched GDB, we get the following backtrace: #0 __fput (file=0xffff0000c17a6400) at /repos/linux/fs/file_table.c:296 #1 0xffff8000082bd1f0 in ____fput (work=<optimized out>) at /repos/linux/fs/file_table.c:348 #2 0x30008000080ade30 [PAC] in ?? () #3 0x30d48000080ade30 in ?? () Backtrace stopped: previous frame identical to this frame (corrupt stack?) With a patched GDB, we get something a lot more meaningful: #0 __fput (file=0xffff0000c1bcfa00) at /repos/linux/fs/file_table.c:296 #1 0xffff8000082bd1f0 in ____fput (work=<optimized out>) at /repos/linux/fs/file_table.c:348 #2 0xffff8000080ade30 [PAC] in task_work_run () at /repos/linux/kernel/task_work.c:179 #3 0xffff80000801db90 [PAC] in resume_user_mode_work (regs=0xffff80000a96beb0) at /repos/linux/include/linux/resume_user_mode.h:49 #4 do_notify_resume (regs=regs@entry=0xffff80000a96beb0, thread_flags=4) at /repos/linux/arch/arm64/kernel/signal.c:1127 #5 0xffff800008fb9974 [PAC] in prepare_exit_to_user_mode (regs=0xffff80000a96beb0) at /repos/linux/arch/arm64/kernel/entry-common.c:137 #6 exit_to_user_mode (regs=0xffff80000a96beb0) at /repos/linux/arch/arm64/kernel/entry-common.c:142 #7 el0_svc (regs=0xffff80000a96beb0) at /repos/linux/arch/arm64/kernel/entry-common.c:638 #8 0xffff800008fb9d34 [PAC] in el0t_64_sync_handler (regs=<optimized out>) at /repos/linux/arch/arm64/kernel/entry-common.c:655 #9 0xffff800008011548 [PAC] in el0t_64_sync () at /repos/linux/arch/arm64/kernel/entry.S:586 Backtrace stopped: Cannot access memory at address 0xffff80000a96c0c8
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README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.
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