From: "Nicholas Piggin" <npiggin@gmail.com>
To: "Benjamin Gray" <bgray@linux.ibm.com>, <linuxppc-dev@lists.ozlabs.org>
Cc: linux-hardening@vger.kernel.org, ajd@linux.ibm.com,
cmr@bluescreens.de, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 06/13] powerpc/dexcr: Add prctl implementation
Date: Tue, 07 Mar 2023 15:12:57 +1000 [thread overview]
Message-ID: <CQZW6V070YIU.3Q6OJGKRPH3KY@bobo> (raw)
In-Reply-To: <20221128024458.46121-7-bgray@linux.ibm.com>
On Mon Nov 28, 2022 at 12:44 PM AEST, Benjamin Gray wrote:
> Adds an initial prctl interface implementation. Unprivileged processes
> can query the current prctl setting, including whether an aspect is
> implemented by the hardware or is permitted to be modified by a setter
> prctl. Editable aspects can be changed by a CAP_SYS_ADMIN privileged
> process.
>
> The prctl setting represents what the process itself has requested, and
> does not account for any overrides. Either the kernel or a hypervisor
> may enforce a different setting for an aspect.
>
> Userspace can access a readonly view of the current DEXCR via SPR 812,
> and a readonly view of the aspects enforced by the hypervisor via
> SPR 455. A bitwise OR of these two SPRs will give the effective
> DEXCR aspect state of the process.
You said (offline) that you were looking at the PR_SPEC_* speculation
control APIs but that this was different enough that you needed a
different one.
It would be good to know what some of those issues were in the
changelog, would be nice to have some docs (could we add something
to spec_ctrl.rst maybe?). I assume at least one difference is that
some of our bits are not speculative but architectural (e.g., the
stack hash check).
I also wonder if we could implement some of the PR_SPEC controls
APIs by mapping relevant DEXCR aspects to them instead of (or as well
as) the DEXCR controls? Or would the PR_SPEC users be amenable to
extensions that make our usage fit a bit better?
I'm just thinking if we can reduce reliance on arch specific APIs a
bit would be nice.
>
> Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
> ---
> arch/powerpc/include/asm/processor.h | 13 +++
> arch/powerpc/kernel/dexcr.c | 133 ++++++++++++++++++++++++++-
> arch/powerpc/kernel/process.c | 6 ++
> 3 files changed, 151 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
> index 2381217c95dc..4c995258f668 100644
> --- a/arch/powerpc/include/asm/processor.h
> +++ b/arch/powerpc/include/asm/processor.h
> @@ -265,6 +265,9 @@ struct thread_struct {
> unsigned long sier2;
> unsigned long sier3;
> unsigned long hashkeyr;
> + unsigned int dexcr_override;
> + unsigned int dexcr_mask;
Hmm, what's the mask doing here? It only gets bits set and never
cleared AFAIKS. What is different between an initial state and a
SET then CLEAR state?
Thanks,
Nick
next prev parent reply other threads:[~2023-03-07 5:28 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-28 2:44 [RFC PATCH 00/13] Add DEXCR support Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 01/13] powerpc/book3s: Add missing <linux/sched.h> include Benjamin Gray
2023-03-07 4:28 ` Nicholas Piggin
2022-11-28 2:44 ` [RFC PATCH 02/13] powerpc: Add initial Dynamic Execution Control Register (DEXCR) support Benjamin Gray
2023-03-07 4:45 ` Nicholas Piggin
2023-03-09 23:46 ` Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 03/13] powerpc/dexcr: Handle hashchk exception Benjamin Gray
2022-11-29 10:39 ` Nicholas Piggin
2022-11-29 22:04 ` Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 04/13] powerpc/dexcr: Support userspace ROP protection Benjamin Gray
2023-03-07 5:05 ` Nicholas Piggin
2023-03-07 5:37 ` Benjamin Gray
2023-03-21 4:51 ` Nicholas Piggin
2022-11-28 2:44 ` [RFC PATCH 05/13] prctl: Define PowerPC DEXCR interface Benjamin Gray
2023-03-07 5:07 ` Nicholas Piggin
2022-11-28 2:44 ` [RFC PATCH 06/13] powerpc/dexcr: Add prctl implementation Benjamin Gray
2023-03-07 5:12 ` Nicholas Piggin [this message]
2022-11-28 2:44 ` [RFC PATCH 07/13] powerpc/dexcr: Add sysctl entry for SBHE system override Benjamin Gray
2023-03-07 5:30 ` Nicholas Piggin
2023-03-07 5:58 ` Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 08/13] powerpc/dexcr: Add enforced userspace ROP protection config Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 09/13] selftests/powerpc: Add more utility macros Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 10/13] selftests/powerpc: Add hashst/hashchk test Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 11/13] selftests/powerpc: Add DEXCR prctl, sysctl interface test Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 12/13] selftests/powerpc: Add DEXCR status utility lsdexcr Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 13/13] Documentation: Document PowerPC kernel DEXCR interface Benjamin Gray
2023-03-07 5:40 ` Nicholas Piggin
2023-03-07 5:52 ` Benjamin Gray
2022-11-28 4:05 ` [RFC PATCH 00/13] Add DEXCR support Russell Currey
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