linux-kernel - Re: [PATCH v2] arm64: update PAC description for kernel

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Date:   Thu, 2 Dec 2021 10:06:47 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Matthias Brugger <matthias.bgg@...il.com>,
        chinwen.chang@...iatek.com, nicholas.tang@...iatek.com,
        james.hsu@...iatek.com, linux-arm-kernel@...ts.infradead.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v2] arm64: update PAC description for kernel

On Wed, Dec 01, 2021 at 11:40:10AM +0800, Kuan-Ying Lee wrote:
> Remove the paragraph which has nothing to do with the kernel and
> add PAC description related to kernel.
> 
> Suggested-by: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com>

This looks good to me.

Catalin/Will, did you want to pick this, or do you want Jonathan to do so?

Mark.

> ---
> v1 -> v2:
>   - Remove compiler option description
>   - Add PAC description for kernel
> 
>  Documentation/arm64/pointer-authentication.rst | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/arm64/pointer-authentication.rst b/Documentation/arm64/pointer-authentication.rst
> index f127666ea3a8..e5dad2e40aa8 100644
> --- a/Documentation/arm64/pointer-authentication.rst
> +++ b/Documentation/arm64/pointer-authentication.rst
> @@ -53,11 +53,10 @@ The number of bits that the PAC occupies in a pointer is 55 minus the
>  virtual address size configured by the kernel. For example, with a
>  virtual address size of 48, the PAC is 7 bits wide.
>  
> -Recent versions of GCC can compile code with APIAKey-based return
> -address protection when passed the -msign-return-address option. This
> -uses instructions in the HINT space (unless -march=armv8.3-a or higher
> -is also passed), and such code can run on systems without the pointer
> -authentication extension.
> +When ARM64_PTR_AUTH_KERNEL is selected, the kernel will be compiled
> +with HINT space pointer authentication instructions protecting
> +function returns. Kernels built with this option will work on hardware
> +with or without pointer authentication support.
>  
>  In addition to exec(), keys can also be reinitialized to random values
>  using the PR_PAC_RESET_KEYS prctl. A bitmask of PR_PAC_APIAKEY,
> -- 
> 2.18.0
>