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Date: Tue, 22 May 2018 15:06:21 -0400
From: Adam Wallis <>
To: Mark Rutland <>,
Subject: Re: [PATCHv2 06/12] arm64: add basic pointer authentication support

On 11/27/2017 11:38 AM, Mark Rutland wrote:
> This patch adds basic support for pointer authentication, allowing
> userspace to make use of APIAKey. The kernel maintains an APIAKey value
> for each process (shared by all threads within), which is initialised to
> a random value at exec() time.
> To describe that address authentication instructions are available, the
> ID_AA64ISAR0.{APA,API} fields are exposed to userspace. A new hwcap,
> APIA, is added to describe that the kernel manages APIAKey.
> Instructions using other keys (APIBKey, APDAKey, APDBKey) are disabled,
> and will behave as NOPs. These may be made use of in future patches.
> No support is added for the generic key (APGAKey), though this cannot be
> trapped or made to behave as a NOP. Its presence is not advertised with
> a hwcap.
> Signed-off-by: Mark Rutland <>
> Cc: Catalin Marinas <>
> Cc: Suzuki K Poulose <>
> Cc: Will Deacon <>
> ---
>  arch/arm64/include/asm/mmu.h          |  5 ++
>  arch/arm64/include/asm/mmu_context.h  | 25 +++++++++-
>  arch/arm64/include/asm/pointer_auth.h | 89 +++++++++++++++++++++++++++++++++++
>  arch/arm64/include/uapi/asm/hwcap.h   |  1 +
>  arch/arm64/kernel/cpufeature.c        | 17 ++++++-
>  arch/arm64/kernel/cpuinfo.c           |  1 +
>  6 files changed, 134 insertions(+), 4 deletions(-)
>  create mode 100644 arch/arm64/include/asm/pointer_auth.h

Mark, I was able to verify that a buffer overflow exploit results in a segfault
with these PAC patches. When I compile the same binary without
"-msign-return-address=none", I am able to successfully overflow the stack and
execute malicious code.


Tested-by: Adam Wallis <>

Adam Wallis
Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

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