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Date:   Tue, 07 Mar 2023 15:07:52 +1000
Message-Id: <CQZW2Z6JU55U.2M24IU59IQZ4D@bobo>
To:     "Benjamin Gray" <bgray@linux.ibm.com>,
        <linuxppc-dev@lists.ozlabs.org>
Cc:     <ajd@linux.ibm.com>, <linux-kernel@vger.kernel.org>,
        <linux-hardening@vger.kernel.org>, <cmr@bluescreens.de>
Subject: Re: [RFC PATCH 05/13] prctl: Define PowerPC DEXCR interface
From:   "Nicholas Piggin" <npiggin@gmail.com>
References: <20221128024458.46121-1-bgray@linux.ibm.com>
 <20221128024458.46121-6-bgray@linux.ibm.com>
In-Reply-To: <20221128024458.46121-6-bgray@linux.ibm.com>
Precedence: bulk

On Mon Nov 28, 2022 at 12:44 PM AEST, Benjamin Gray wrote:
> Adds the definitions and generic handler for prctl control of the
> PowerPC Dynamic Execution Control Register (DEXCR).

Assuming we'd go with the later prctl patches, this prep patch
is nice way to split out some of the mechanism.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

>
> Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
> ---
>  include/uapi/linux/prctl.h | 14 ++++++++++++++
>  kernel/sys.c               | 16 ++++++++++++++++
>  2 files changed, 30 insertions(+)
>
> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index a5e06dcbba13..b4720e8de6f3 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -281,6 +281,20 @@ struct prctl_mm_map {
>  # define PR_SME_VL_LEN_MASK		0xffff
>  # define PR_SME_VL_INHERIT		(1 << 17) /* inherit across exec */
> =20
> +/* PowerPC Dynamic Execution Control Register (DEXCR) controls */
> +#define PR_PPC_GET_DEXCR		65
> +#define PR_PPC_SET_DEXCR		66
> +/* DEXCR aspect to act on */
> +# define PR_PPC_DEXCR_SBHE		0 /* Speculative branch hint enable */
> +# define PR_PPC_DEXCR_IBRTPD		1 /* Indirect branch recurrent target pred=
iction disable */
> +# define PR_PPC_DEXCR_SRAPD		2 /* Subroutine return address prediction d=
isable */
> +# define PR_PPC_DEXCR_NPHIE		3 /* Non-privileged hash instruction enable=
 */
> +/* Action to apply / return */
> +# define PR_PPC_DEXCR_PRCTL		(1 << 0)
> +# define PR_PPC_DEXCR_SET_ASPECT	(1 << 1)
> +# define PR_PPC_DEXCR_FORCE_SET_ASPECT	(1 << 2)
> +# define PR_PPC_DEXCR_CLEAR_ASPECT	(1 << 3)
> +
>  #define PR_SET_VMA		0x53564d41
>  # define PR_SET_VMA_ANON_NAME		0
> =20
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 5fd54bf0e886..55b8f7369059 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -139,6 +139,12 @@
>  #ifndef GET_TAGGED_ADDR_CTRL
>  # define GET_TAGGED_ADDR_CTRL()		(-EINVAL)
>  #endif
> +#ifndef PPC_GET_DEXCR_ASPECT
> +# define PPC_GET_DEXCR_ASPECT(a, b)	(-EINVAL)
> +#endif
> +#ifndef PPC_SET_DEXCR_ASPECT
> +# define PPC_SET_DEXCR_ASPECT(a, b, c)	(-EINVAL)
> +#endif
> =20
>  /*
>   * this is where the system-wide overflow UID and GID are defined, for
> @@ -2623,6 +2629,16 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long,=
 arg2, unsigned long, arg3,
>  		error =3D sched_core_share_pid(arg2, arg3, arg4, arg5);
>  		break;
>  #endif
> +	case PR_PPC_GET_DEXCR:
> +		if (arg3 || arg4 || arg5)
> +			return -EINVAL;
> +		error =3D PPC_GET_DEXCR_ASPECT(me, arg2);
> +		break;
> +	case PR_PPC_SET_DEXCR:
> +		if (arg4 || arg5)
> +			return -EINVAL;
> +		error =3D PPC_SET_DEXCR_ASPECT(me, arg2, arg3);
> +		break;
>  	case PR_SET_VMA:
>  		error =3D prctl_set_vma(arg2, arg3, arg4, arg5);
>  		break;
> --=20
> 2.38.1