unable to fetch pauth registers: Invalid argument.

[Heinrich Schuchardt]

I am running Ubuntu Lunar on an arm64 Lenovo X13s using the kernel 6.2.0-1003-laptop from ppa:ubuntu-concept/x13s. The kernel is configured with CONFIG_ARM64_PTR_AUTH=y.

Debugging a trivial hello world program fails:

GNU gdb (Ubuntu 13.1-2ubuntu2) 13.1
Reading symbols from ./test...
(gdb) r
Starting program: /home/user/temp/test
unable to fetch pauth registers: Invalid argument.

The message relates to this statement:

gdb/aarch64-linux-nat.c:371:
ret = ptrace (PTRACE_GETREGSET, tid, NT_ARM_PAC_MASK, &iovec);

When using

set tdesc filename target.xml

with a target.xml file without the org.gnu.gdb.aarch64.pauth feature debugging works fine.

[Heinrich Schuchardt (xypron)]

https://<email address hidden>/
introduced hwcaps PACA (for address authentication) and PACG (for generic
authentication). These are present in /proc/cpuinfo:

Features:
fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics fphp asimdhp cpuid asimdrdm lrcpc dcpop asimddp uscat ilrcpc flagm paca pacg

[Heinrich Schuchardt (xypron)]

The problem to read the pauth registers is reproducible with a simple C program:

#define _GNU_SOURCE
#include <elf.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ptrace.h>
#include <sys/uio.h>
#include <sys/wait.h>
#include <unistd.h>

#define LEN 16384

int main()
{
        long ret;
        struct iovec iovec;
        pid_t pid;

        pid = fork();
        if (!pid) {
                sleep(1);
                return 0;
        }
        ret = ptrace(PTRACE_ATTACH, pid, NULL, NULL);
        if (ret == -1) {
                perror("PTRACE_ATTACH failed");
                return 1;
        }
        iovec.iov_base = malloc(LEN);
        iovec.iov_len = LEN;
        wait(NULL);
        // ret = ptrace (PTRACE_GETREGSET, pid, NT_PRSTATUS, &iovec);
        ret = ptrace (PTRACE_GETREGSET, pid, NT_ARM_PAC_MASK, &iovec);
        if (ret == -1) {
                perror("PTRACE_GETREGSET");
                return 1;
        }
        printf("PTRACE_GETREGSET succeeded\n");
        return 0;
}