Re: [kvm-unit-tests RFC PATCH 08/16] lib: arm/arm64: Refuse to disable the MMU with non-identity stack pointer

From: Andrew Jones <drjones@redhat.com>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: kvm@vger.kernel.org, maz@kernel.org, andre.przywara@arm.com,
	pbonzini@redhat.com, kvmarm@lists.cs.columbia.edu
Subject: Re: [kvm-unit-tests RFC PATCH 08/16] lib: arm/arm64: Refuse to disable the MMU with non-identity stack pointer
Date: Wed, 28 Aug 2019 16:55:26 +0200	[thread overview]
Message-ID: <20190828145526.g6xlotkhial5tv57@kamzik.brq.redhat.com> (raw)
In-Reply-To: <1566999511-24916-9-git-send-email-alexandru.elisei@arm.com>

On Wed, Aug 28, 2019 at 02:38:23PM +0100, Alexandru Elisei wrote:
> When the MMU is off, all addresses are physical addresses. If the stack
> pointer is not an identity mapped address (the virtual address is not the
> same as the physical address), then we end up trying to access an invalid
> memory region. This can happen if we call mmu_disable from a secondary CPU,
> which has its stack allocated from the vmalloc region.
> 
> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> ---
>  lib/arm/mmu.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/lib/arm/mmu.c b/lib/arm/mmu.c
> index 3d38c8397f5a..161f7a8e607c 100644
> --- a/lib/arm/mmu.c
> +++ b/lib/arm/mmu.c
> @@ -66,8 +66,12 @@ void mmu_enable(pgd_t *pgtable)
>  extern void asm_mmu_disable(void);
>  void mmu_disable(void)
>  {
> +	unsigned long sp = current_stack_pointer;
>  	int cpu = current_thread_info()->cpu;
>  
> +	assert_msg(__virt_to_phys(sp) == sp,
> +			"Attempting to disable MMU with non-identity mapped stack");
> +
>  	mmu_mark_disabled(cpu);
>  
>  	asm_mmu_disable();
> -- 
> 2.7.4
>

Reviewed-by: Andrew Jones <drjones@redhat.com>
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