linux-kernel - Re: [RFC PATCH 7/7 v1]powerpc: Deliver SEGV signal on protection key violation.

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Message-ID: <87zid8uqnu.fsf@concordia.ellerman.id.au>
Date:   Fri, 16 Jun 2017 21:18:29 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Ram Pai <linuxram@...ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Cc:     benh@...nel.crashing.org, paulus@...ba.org,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, dave.hansen@...el.com, hbabu@...ibm.com,
        linuxram@...ibm.com
Subject: Re: [RFC PATCH 7/7 v1]powerpc: Deliver SEGV signal on protection key violation.

Ram Pai <linuxram@...ibm.com> writes:
> diff --git a/arch/powerpc/include/uapi/asm/ptrace.h b/arch/powerpc/include/uapi/asm/ptrace.h
> index 8036b38..109d0c2 100644
> --- a/arch/powerpc/include/uapi/asm/ptrace.h
> +++ b/arch/powerpc/include/uapi/asm/ptrace.h
> @@ -49,6 +49,8 @@ struct pt_regs {
>  	unsigned long dar;		/* Fault registers */
>  	unsigned long dsisr;		/* on 4xx/Book-E used for ESR */
>  	unsigned long result;		/* Result of a system call */
> +	unsigned long dscr;		/* contents of the DSCR register */
> +	unsigned long amr;		/* contents of AMR register */
>  };

You can't change pt_regs, it's ABI.

> @@ -109,7 +111,8 @@ struct pt_regs {
>  #define PT_DSISR 42
>  #define PT_RESULT 43
>  #define PT_DSCR 44
> -#define PT_REGS_COUNT 44
> +#define PT_AMR 45
> +#define PT_REGS_COUNT 45

You can add PT_AMR, but it has to be synthetic like DSCR, ie. not
actually in pt_regs but available via ptrace.

But do we want to do that? How does the x86 code export the key(s) of a
process? Or doesn't it?

cheers