From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: [PATCH v9 3/3] arm64: Relax Documentation/arm64/tagged-pointers.rst Date: Wed, 21 Aug 2019 17:47:30 +0100 Message-ID: <20190821164730.47450-4-catalin.marinas@arm.com> References: <20190821164730.47450-1-catalin.marinas@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190821164730.47450-1-catalin.marinas@arm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Cc: linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, Szabolcs Nagy , Andrey Konovalov , Kevin Brodsky , Will Deacon , Dave Hansen , Andrew Morton , Vincenzo Frascino , Will Deacon , Dave P Martin List-Id: linux-arch.vger.kernel.org From: Vincenzo Frascino 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 Cc: Szabolcs Nagy Cc: Kevin Brodsky Acked-by: Andrey Konovalov Signed-off-by: Vincenzo Frascino Co-developed-by: Catalin Marinas Signed-off-by: Catalin Marinas --- 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 -------------------- From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.110.172]:33482 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729733AbfHUQrt (ORCPT ); Wed, 21 Aug 2019 12:47:49 -0400 From: Catalin Marinas Subject: [PATCH v9 3/3] arm64: Relax Documentation/arm64/tagged-pointers.rst Date: Wed, 21 Aug 2019 17:47:30 +0100 Message-ID: <20190821164730.47450-4-catalin.marinas@arm.com> In-Reply-To: <20190821164730.47450-1-catalin.marinas@arm.com> References: <20190821164730.47450-1-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Cc: Andrew Morton , Vincenzo Frascino , Will Deacon , Andrey Konovalov , Szabolcs Nagy , Kevin Brodsky , Dave P Martin , Dave Hansen , linux-doc@vger.kernel.org, linux-arch@vger.kernel.org, Will Deacon Message-ID: <20190821164730.9lW0LSoa98egZos4opxI4HQFCYUjrsVfMwxgOoYekg8@z> From: Vincenzo Frascino 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 Cc: Szabolcs Nagy Cc: Kevin Brodsky Acked-by: Andrey Konovalov Signed-off-by: Vincenzo Frascino Co-developed-by: Catalin Marinas Signed-off-by: Catalin Marinas --- 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 --------------------