linux-kernel - [PATCH 0/3] arm64/ptrace: allow to get all registers on syscall traps

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Date:   Tue, 19 Jan 2021 14:06:34 -0800
From:   Andrei Vagin <avagin@...il.com>
To:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Andrei Vagin <avagin@...il.com>
Subject: [PATCH 0/3] arm64/ptrace: allow to get all registers on syscall traps

Right now, ip/r12 for AArch32 and x7 for AArch64 is used to indicate
whether or not the stop has been signalled from syscall entry or syscall
exit. This means that:

- Any writes by the tracer to this register during the stop are
  ignored/discarded.

- The actual value of the register is not available during the stop,
  so the tracer cannot save it and restore it later.

This series introduces NT_ARM_PRSTATUS to get all registers and makes it
possible to change ip/r12 and x7 registers when tracee is stopped in
syscall traps.

For applications like the user-mode Linux or gVisor, it is critical to
have access to the full set of registers in any moment. For example,
they need to change values of all registers to emulate rt_sigreturn and
they need to have the full set of registers to build a signal frame.

Andrei Vagin (3):
  arm64/ptrace: don't clobber task registers on syscall entry/exit traps
  arm64/ptrace: introduce NT_ARM_PRSTATUS to get a full set of registers
  selftest/arm64/ptrace: add a test for NT_ARM_PRSTATUS

 arch/arm64/include/asm/ptrace.h               |   5 +
 arch/arm64/kernel/ptrace.c                    | 130 +++++++++++-----
 include/uapi/linux/elf.h                      |   1 +
 tools/testing/selftests/arm64/Makefile        |   2 +-
 tools/testing/selftests/arm64/ptrace/Makefile |   6 +
 .../arm64/ptrace/ptrace_syscall_regs_test.c   | 142 ++++++++++++++++++
 6 files changed, 246 insertions(+), 40 deletions(-)
 create mode 100644 tools/testing/selftests/arm64/ptrace/Makefile
 create mode 100644 tools/testing/selftests/arm64/ptrace/ptrace_syscall_regs_test.c

-- 
2.29.2