From: Quan Zhou <zhouquan@xxxxxxxxxxx>
Due to the path that modifies a0 in syscall_enter_from_user_mode before the
actual execution of syscall_handler [1], the kernel currently saves a0 to
orig_a0 at the entry point of do_trap_ecall_u as an original copy of a0.
Once the syscall is interrupted and later resumed, the restarted syscall
will use orig_a0 to continue execution.
The above rules generally apply except for ptrace(PTRACE_SETREGSET,),
where the kernel will ignore the tracer's setting of tracee/a0 and
will restart with the tracee's original a0 value. For the current
kernel implementation of ptrace, projects like CRIU/Proot will
encounter issues where the a0 setting becomes ineffective when
performing ptrace(PTRACE_{SET/GET}REGSET,).
Here is a suggested solution, expose orig_a0 to userspace so that ptrace
can choose whether to set orig_a0 based on the actual scenario. In fact,
x86/orig_eax and loongArch/orig_a0 have adopted similar solutions.
[1] link: https://lore.kernel.org/lkml/20230403-crisping-animosity-04ed8a45c625@spud/T/
Quan Zhou (2):
riscv: Expose orig_a0 in the user_regs_struct structure
riscv: selftests: Add a ptrace test to check a0 of restarted syscall
arch/riscv/include/asm/ptrace.h | 4 +-
arch/riscv/include/uapi/asm/ptrace.h | 2 +
tools/testing/selftests/riscv/Makefile | 2 +-
tools/testing/selftests/riscv/abi/.gitignore | 1 +
tools/testing/selftests/riscv/abi/Makefile | 12 ++
.../riscv/abi/ptrace_restart_syscall.c | 148 ++++++++++++++++++
6 files changed, 166 insertions(+), 3 deletions(-)
create mode 100644 tools/testing/selftests/riscv/abi/.gitignore
create mode 100644 tools/testing/selftests/riscv/abi/Makefile
create mode 100644 tools/testing/selftests/riscv/abi/ptrace_restart_syscall.c
base-commit: 6ba59ff4227927d3a8530fc2973b80e94b54d58f
--
2.34.1
