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From: Michael Ellerman <mpe@ellerman.id.au>
To: Russell Currey <ruscur@russell.cc>, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc/powernv/idle: Restore IAMR after idle
Date: Thu, 07 Feb 2019 15:29:13 +1100
Message-ID: <875ztwkyqu.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <20190206062837.26917-1-ruscur@russell.cc>

Russell Currey <ruscur@russell.cc> writes:
> Without restoring the IAMR after idle, execution prevention on POWER9
> with Radix MMU is overwritten and the kernel can freely execute userspace without
> faulting.
>
> This is necessary when returning from any stop state that modifies user
> state, as well as hypervisor state.
>
> To test how this fails without this patch, load the lkdtm driver and
> do the following:
>
>    echo EXEC_USERSPACE > /sys/kernel/debug/provoke-crash/DIRECT
>
> which won't fault, then boot the kernel with powersave=off, where it
> will fault.  Applying this patch will fix this.
>
> Fixes: 3b10d0095a1e ("powerpc/mm/radix: Prevent kernel execution of user
> space")

Don't word wrap the fixes line please.

> Cc: <stable@vger.kernel.org>
> Signed-off-by: Russell Currey <ruscur@russell.cc>
> ---
>  arch/powerpc/include/asm/cpuidle.h |  1 +
>  arch/powerpc/kernel/asm-offsets.c  |  1 +
>  arch/powerpc/kernel/idle_book3s.S  | 20 ++++++++++++++++++++
>  3 files changed, 22 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/cpuidle.h b/arch/powerpc/include/asm/cpuidle.h
> index 43e5f31fe64d..ad67dbe59498 100644
> --- a/arch/powerpc/include/asm/cpuidle.h
> +++ b/arch/powerpc/include/asm/cpuidle.h
> @@ -77,6 +77,7 @@ struct stop_sprs {
>  	u64 mmcr1;
>  	u64 mmcr2;
>  	u64 mmcra;
> +	u64 iamr;
>  };

We don't actually need to put this in the paca anymore.

> diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
> index 7f5ac2e8581b..bb4f552f6c7e 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -200,6 +200,12 @@ pnv_powersave_common:
>  	/* Continue saving state */
>  	SAVE_GPR(2, r1)
>  	SAVE_NVGPRS(r1)
> +
> +BEGIN_FTR_SECTION
> +	mfspr	r5, SPRN_IAMR
> +	std	r5, STOP_IAMR(r13)
> +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)

We have space for a full pt_regs on the stack, and we're not using it
all.

We don't have a specific slot for the IAMR (we may want to in future),
but for now you could follow the time-honoured tradition of (ab)using
the _DAR slot, with an appropriate comment.

cheers

  reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-06  6:28 Russell Currey
2019-02-07  4:29 ` Michael Ellerman [this message]
2019-02-07  6:28   ` Russell Currey
2019-02-07  5:08 ` Nicholas Piggin
2019-02-07  6:33   ` Russell Currey
2019-02-07 16:37     ` Thiago Jung Bauermann
2019-02-07 22:38       ` Russell Currey
2019-02-08  1:04   ` Michael Ellerman
2019-02-19  4:21     ` Nicholas Piggin
2019-02-20  6:04       ` Akshay Adiga
2019-02-20 11:18         ` Russell Currey
2019-02-20  7:15 ` Akshay Adiga
2019-02-20 11:25   ` Russell Currey
2019-02-20  8:58 ` Akshay Adiga
2019-02-20 11:20   ` Russell Currey

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