From ea08eeccae9297f7aabd2ef7f0c2517ac4549acc Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Tue, 20 Feb 2024 01:18:26 +0000
Subject: [PATCH] write in 30M
---
kernel/Documentation/arm64/tagged-address-abi.rst | 24 +++++++++++++++++-------
1 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/kernel/Documentation/arm64/tagged-address-abi.rst b/kernel/Documentation/arm64/tagged-address-abi.rst
index 4a9d9c7..7d25524 100644
--- a/kernel/Documentation/arm64/tagged-address-abi.rst
+++ b/kernel/Documentation/arm64/tagged-address-abi.rst
@@ -45,14 +45,24 @@
1. User addresses not accessed by the kernel but used for address space
management (e.g. ``mprotect()``, ``madvise()``). The use of valid
- tagged pointers in this context is allowed with the exception of
- ``brk()``, ``mmap()`` and the ``new_address`` argument to
- ``mremap()`` as these have the potential to alias with existing
- user addresses.
+ tagged pointers in this context is allowed with these exceptions:
- NOTE: This behaviour changed in v5.6 and so some earlier kernels may
- incorrectly accept valid tagged pointers for the ``brk()``,
- ``mmap()`` and ``mremap()`` system calls.
+ - ``brk()``, ``mmap()`` and the ``new_address`` argument to
+ ``mremap()`` as these have the potential to alias with existing
+ user addresses.
+
+ NOTE: This behaviour changed in v5.6 and so some earlier kernels may
+ incorrectly accept valid tagged pointers for the ``brk()``,
+ ``mmap()`` and ``mremap()`` system calls.
+
+ - The ``range.start``, ``start`` and ``dst`` arguments to the
+ ``UFFDIO_*`` ``ioctl()``s used on a file descriptor obtained from
+ ``userfaultfd()``, as fault addresses subsequently obtained by reading
+ the file descriptor will be untagged, which may otherwise confuse
+ tag-unaware programs.
+
+ NOTE: This behaviour changed in v5.14 and so some earlier kernels may
+ incorrectly accept valid tagged pointers for this system call.
2. User addresses accessed by the kernel (e.g. ``write()``). This ABI
relaxation is disabled by default and the application thread needs to
--
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