[PATCH v9 7/8] arm64: update Documentation/arm64/tagged-pointers.txt

From: Andrey Konovalov <andreyknvl@google.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Kees Cook <keescook@chromium.org>,
	Kate Stewart <kstewart@linuxfoundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Shuah Khan <shuah@kernel.org>,
	linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Dmitry Vyukov <dvyukov@google.com>,
	Kostya Serebryany <kcc@google.com>,
	Evgeniy Stepanov <eugenis@google.com>,
	Lee Smith <Lee.Smith@arm.com>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
	Jacob Bramley <Jacob.Bramley@arm.com>,
	Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>,
	Chintan Pandya <cpandya@codeaurora.org>,
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
	Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH v9 7/8] arm64: update Documentation/arm64/tagged-pointers.txt
Date: Mon, 10 Dec 2018 13:51:04 +0100	[thread overview]
Message-ID: <5b08153a9d69a5aa958071dcc5477c881f56dcde.1544445454.git.andreyknvl@google.com> (raw)
In-Reply-To: <cover.1544445454.git.andreyknvl@google.com>

Document the changes in Documentation/arm64/tagged-pointers.txt.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 Documentation/arm64/tagged-pointers.txt | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/Documentation/arm64/tagged-pointers.txt b/Documentation/arm64/tagged-pointers.txt
index a25a99e82bb1..f4cf1f5cf362 100644
--- a/Documentation/arm64/tagged-pointers.txt
+++ b/Documentation/arm64/tagged-pointers.txt
@@ -17,13 +17,22 @@ this byte for application use.
 Passing tagged addresses to the kernel
 --------------------------------------
 
-All interpretation of userspace memory addresses by the kernel assumes
-an address tag of 0x00.
+The kernel supports tags in pointer arguments (including pointers in
+structures) for a limited set of syscalls, the exceptions are:
 
-This includes, but is not limited to, addresses found in:
+ - memory syscalls: brk, madvise, mbind, mincore, mlock, mlock2, move_pages,
+   mprotect, mremap, msync, munlock, munmap, pkey_mprotect, process_vm_readv,
+   process_vm_writev, remap_file_pages;
 
- - pointer arguments to system calls, including pointers in structures
-   passed to system calls,
+ - ioctls that accept user pointers that describe virtual memory ranges;
+
+ - TCP_ZEROCOPY_RECEIVE setsockopt.
+
+The kernel supports tags in user fault addresses. However the fault_address
+field in the sigcontext struct will contain an untagged address.
+
+All other interpretations of userspace memory addresses by the kernel
+assume an address tag of 0x00, in particular:
 
  - the stack pointer (sp), e.g. when interpreting it to deliver a
    signal,
@@ -33,11 +42,7 @@ This includes, but is not limited to, addresses found in:
 
 Using non-zero address tags in any of these locations may result in an
 error code being returned, a (fatal) signal being raised, or other modes
-of failure.
-
-For these reasons, passing non-zero address tags to the kernel via
-system calls is forbidden, and using a non-zero address tag for sp is
-strongly discouraged.
+of failure. Using a non-zero address tag for sp is strongly discouraged.
 
 Programs maintaining a frame pointer and frame records that use non-zero
 address tags may suffer impaired or inaccurate debug and profiling
-- 
2.20.0.rc2.403.gdbc3b29805-goog

