linux-kernel - [PATCH v16 0/4] Checkpoint Support for Syscall User Dispatch

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Message-Id: <20230407171834.3558-1-gregory.price@memverge.com>
Date:   Fri,  7 Apr 2023 13:18:30 -0400
From:   Gregory Price <gourry.memverge@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-doc@...r.kernel.org, linux-arch@...r.kernel.org,
        oleg@...hat.com, avagin@...il.com, peterz@...radead.org,
        luto@...nel.org, krisman@...labora.com, tglx@...utronix.de,
        corbet@....net, shuah@...nel.org, catalin.marinas@....com,
        arnd@...db.de, Gregory Price <gregory.price@...verge.com>
Subject: [PATCH v16 0/4] Checkpoint Support for Syscall User Dispatch

This appears to be in a good state now.  Not sure which branch
I should seek to have this pulled through, or what else needs to
be done to push this forward.

v16: pick up review tags, mild comment change

v15: drop task_access_ok variant, instead prefer to just untag the
     selector address when validating the user pointer.

v14: implement task_access_ok variant for cross-task pointer checks

v13: sizeof consistency and cosmetic changes in patch 2

v12: split test into its own patch
     change from padding a u8 to using a u64
     casting issues
     checkpatch.pl

[truncating version history]

Syscall user dispatch makes it possible to cleanly intercept system
calls from user-land.  However, most transparent checkpoint software
presently leverages some combination of ptrace and system call
injection to place software in a ready-to-checkpoint state.

If Syscall User Dispatch is enabled at the time of being quiesced,
injected system calls will subsequently be interposed upon and
dispatched to the task's signal handler.

Patch summary:

- Refactor configuration setting interface to operate on a task
  rather than current, so the set and error paths can be consolidated

- Untag the selector address when being set in order to enable an
  untagged tracer to set a tagged tracee's syscall dispatch selector.
  Otherwise an untagged tracer will always fail to set a tagged address.

- Implement a getter interface for Syscall User Dispatch config info.
  To resume successfully, the checkpoint/resume software has to
  save and restore this information.  Presently this configuration
  is write-only, with no way for C/R software to save it.

  This was done in ptrace because syscall user dispatch is not part of
  uapi. The syscall_user_dispatch_config structure was added to the
  ptrace exports.

- Selftest for the new feature


Gregory Price (4):
  syscall_user_dispatch: helper function to operate on given task
  syscall user dispatch: untag selector addresses before access_ok
  ptrace,syscall_user_dispatch: checkpoint/restore support for SUD
  selftest,ptrace: Add selftest for syscall user dispatch config api

 .../admin-guide/syscall-user-dispatch.rst     |  4 +
 include/linux/syscall_user_dispatch.h         | 18 +++++
 include/uapi/linux/ptrace.h                   | 29 ++++++++
 kernel/entry/syscall_user_dispatch.c          | 74 ++++++++++++++++---
 kernel/ptrace.c                               |  9 +++
 tools/testing/selftests/ptrace/.gitignore     |  1 +
 tools/testing/selftests/ptrace/Makefile       |  2 +-
 tools/testing/selftests/ptrace/get_set_sud.c  | 72 ++++++++++++++++++
 8 files changed, 199 insertions(+), 10 deletions(-)
 create mode 100644 tools/testing/selftests/ptrace/get_set_sud.c

-- 
2.39.1