From 6d0020873deb2f2c4e0965dc2ebf227bc1db3140 Mon Sep 17 00:00:00 2001 From: Luis Machado Date: Sun, 11 Sep 2022 20:47:18 +0100 Subject: [aarch64] Enable pointer authentication support for aarch64 bare metal/kernel mode addresses 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=) 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=) 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=) 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 --- gdb/aarch64-tdep.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'gdb/aarch64-tdep.h') diff --git a/gdb/aarch64-tdep.h b/gdb/aarch64-tdep.h index 97b8d0c..ae38327 100644 --- a/gdb/aarch64-tdep.h +++ b/gdb/aarch64-tdep.h @@ -94,6 +94,8 @@ struct aarch64_gdbarch_tdep : gdbarch_tdep_base } int pauth_reg_base = 0; + /* Number of pauth masks. */ + int pauth_reg_count = 0; int ra_sign_state_regnum = 0; /* Returns true if the target supports pauth. */ -- cgit v1.1