From: Catalin Marinas <catalin.marinas@arm.com>
To: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org
Cc: linux-arch@vger.kernel.org, linux-doc@vger.kernel.org,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
Andrey Konovalov <andreyknvl@google.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
Will Deacon <will.deacon@arm.com>,
Dave Hansen <dave.hansen@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Will Deacon <will@kernel.org>,
Dave P Martin <Dave.Martin@arm.com>
Subject: [PATCH v9 3/3] arm64: Relax Documentation/arm64/tagged-pointers.rst
Date: Wed, 21 Aug 2019 17:47:30 +0100 [thread overview]
Message-ID: <20190821164730.47450-4-catalin.marinas@arm.com> (raw)
In-Reply-To: <20190821164730.47450-1-catalin.marinas@arm.com>
From: Vincenzo Frascino <vincenzo.frascino@arm.com>
On AArch64 the TCR_EL1.TBI0 bit is set by default, allowing userspace
(EL0) to perform memory accesses through 64-bit pointers with a non-zero
top byte. However, such pointers were not allowed at the user-kernel
syscall ABI boundary.
With the Tagged Address ABI patchset, it is now possible to pass tagged
pointers to the syscalls. Relax the requirements described in
tagged-pointers.rst to be compliant with the behaviours guaranteed by
the AArch64 Tagged Address ABI.
Cc: Will Deacon <will.deacon@arm.com>
Cc: Szabolcs Nagy <szabolcs.nagy@arm.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Acked-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Co-developed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
---
Documentation/arm64/tagged-pointers.rst | 23 ++++++++++++++++-------
1 file changed, 16 insertions(+), 7 deletions(-)
diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst
index 2acdec3ebbeb..04f2ba9b779e 100644
--- a/Documentation/arm64/tagged-pointers.rst
+++ b/Documentation/arm64/tagged-pointers.rst
@@ -20,7 +20,9 @@ Passing tagged addresses to the kernel
--------------------------------------
All interpretation of userspace memory addresses by the kernel assumes
-an address tag of 0x00.
+an address tag of 0x00, unless the application enables the AArch64
+Tagged Address ABI explicitly
+(Documentation/arm64/tagged-address-abi.rst).
This includes, but is not limited to, addresses found in:
@@ -33,13 +35,15 @@ This includes, but is not limited to, addresses found in:
- the frame pointer (x29) and frame records, e.g. when interpreting
them to generate a backtrace or call graph.
-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.
+Using non-zero address tags in any of these locations when the
+userspace application did not enable the AArch64 Tagged Address ABI 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.
+For these reasons, when the AArch64 Tagged Address ABI is disabled,
+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.
Programs maintaining a frame pointer and frame records that use non-zero
address tags may suffer impaired or inaccurate debug and profiling
@@ -59,6 +63,11 @@ be preserved.
The architecture prevents the use of a tagged PC, so the upper byte will
be set to a sign-extension of bit 55 on exception return.
+This behaviour is maintained when the AArch64 Tagged Address ABI is
+enabled. In addition, with the exceptions above, the kernel will
+preserve any non-zero tags passed by the user via syscalls and stored in
+kernel data structures (e.g. ``set_robust_list()``, ``sigaltstack()``).
+
Other considerations
--------------------
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-08-21 16:48 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-21 16:47 [PATCH v9 0/3] arm64 tagged address ABI Catalin Marinas
2019-08-21 16:47 ` [PATCH v9 1/3] mm: untag user pointers in mmap/munmap/mremap/brk Catalin Marinas
2019-08-21 16:47 ` [PATCH v9 2/3] arm64: Define Documentation/arm64/tagged-address-abi.rst Catalin Marinas
2019-08-21 16:57 ` Andrey Konovalov
2019-08-22 9:38 ` Kevin Brodsky
2019-08-21 17:35 ` Will Deacon
2019-08-22 14:17 ` [PATCH] arm64: Add tagged-address-abi.rst to index.rst Vincenzo Frascino
2019-08-21 16:47 ` Catalin Marinas [this message]
2019-08-21 17:33 ` [PATCH v9 3/3] arm64: Relax Documentation/arm64/tagged-pointers.rst Will Deacon
2019-08-21 18:46 ` Dave Martin
2019-08-22 15:55 ` Catalin Marinas
2019-08-22 16:37 ` Dave Martin
2019-08-23 16:19 ` Catalin Marinas
2019-08-23 16:32 ` Dave Martin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190821164730.47450-4-catalin.marinas@arm.com \
--to=catalin.marinas@arm.com \
--cc=Dave.Martin@arm.com \
--cc=akpm@linux-foundation.org \
--cc=andreyknvl@google.com \
--cc=dave.hansen@intel.com \
--cc=kevin.brodsky@arm.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=szabolcs.nagy@arm.com \
--cc=vincenzo.frascino@arm.com \
--cc=will.deacon@arm.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).