linux-kernel - Re: [PATCH v3 09/14] arm64: Enable memory encrypt for Realms

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Date: Fri, 21 Jun 2024 10:05:39 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Steven Price <steven.price@....com>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
	James Morse <james.morse@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Zenghui Yu <yuzenghui@...wei.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Joey Gouly <joey.gouly@....com>,
	Alexandru Elisei <alexandru.elisei@....com>,
	Christoffer Dall <christoffer.dall@....com>,
	Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
Subject: Re: [PATCH v3 09/14] arm64: Enable memory encrypt for Realms

On Wed, Jun 05, 2024 at 10:30:01AM +0100, Steven Price wrote:
> +static int __set_memory_encrypted(unsigned long addr,
> +				  int numpages,
> +				  bool encrypt)
> +{
> +	unsigned long set_prot = 0, clear_prot = 0;
> +	phys_addr_t start, end;
> +	int ret;
> +
> +	if (!is_realm_world())
> +		return 0;
> +
> +	if (!__is_lm_address(addr))
> +		return -EINVAL;
> +
> +	start = __virt_to_phys(addr);
> +	end = start + numpages * PAGE_SIZE;
> +
> +	/*
> +	 * Break the mapping before we make any changes to avoid stale TLB
> +	 * entries or Synchronous External Aborts caused by RIPAS_EMPTY
> +	 */
> +	ret = __change_memory_common(addr, PAGE_SIZE * numpages,
> +				     __pgprot(0),
> +				     __pgprot(PTE_VALID));
> +
> +	if (encrypt) {
> +		clear_prot = PROT_NS_SHARED;
> +		ret = rsi_set_memory_range_protected(start, end);
> +	} else {
> +		set_prot = PROT_NS_SHARED;
> +		ret = rsi_set_memory_range_shared(start, end);
> +	}

While reading Michael's replies, it occurred to me that we need check
the error paths. Here for example we ignore the return code from
__change_memory_common() by overriding the 'ret' variable.

I think the only other place where we don't check at all is the ITS
allocation/freeing. Freeing is more interesting as I think we should not
release the page back to the kernel if we did not manage to restore the
original state. Better have a memory leak than data leak.

-- 
Catalin