Re: [PATCH] arm64: permit ACPI core to map kernel memory used for table overrides

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Tue, 29 Sep 2020 15:25:22 +0200
Ard Biesheuvel <ardb@kernel.org> wrote:

> Jonathan reports that the strict policy for memory mapped by the
> ACPI core breaks the use case of passing ACPI table overrides via
> initramfs. This is due to the fact that the memory type used for
> loading the initramfs in memory is not recognized as a memory type
> that is typically used by firmware to pass firmware tables.
> 
> Since the purpose of the strict policy is to ensure that no AML or
> other ACPI code can manipulate any memory that is used by the kernel
> to keep its internal state or the state of user tasks, we can relax
> the permission check, and allow mappings of memory that is reserved
> and marked as NOMAP via memblock, and therefore not covered by the
> linear mapping to begin with.
> 

My over enthusiastic filters went and swept this one away so I missed it.
Catalin, thanks for pointing it out!

Anyhow, retested and still looks good.   Slightly tighter check makes
sense.

> Cc: Sudeep Holla <sudeep.holla@arm.com>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Fixes: 1583052d111f ("arm64/acpi: disallow AML memory opregions to access kernel memory")
> Fixes: 325f5585ec36 ("arm64/acpi: disallow writeable AML opregion mapping for EFI code regions")
> Reported-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
>  arch/arm64/kernel/acpi.c | 22 ++++++++++++++++++--
>  include/linux/acpi.h     |  2 +-
>  2 files changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> index a85174d05473..cada0b816c8a 100644
> --- a/arch/arm64/kernel/acpi.c
> +++ b/arch/arm64/kernel/acpi.c
> @@ -298,8 +298,21 @@ void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
>  		case EFI_BOOT_SERVICES_DATA:
>  		case EFI_CONVENTIONAL_MEMORY:
>  		case EFI_PERSISTENT_MEMORY:
> -			pr_warn(FW_BUG "requested region covers kernel memory @ %pa\n", &phys);
> -			return NULL;
> +			if (memblock_is_map_memory(phys) ||
> +			    !memblock_is_region_memory(phys, size)) {
> +				pr_warn(FW_BUG "requested region covers kernel memory @ %pa\n", &phys);
> +				return NULL;
> +			}
> +			/*
> +			 * Mapping kernel memory is permitted if the region in
> +			 * question is covered by a single memblock with the
> +			 * NOMAP attribute set: this enables the use of ACPI
> +			 * table overrides passed via initramfs, which are
> +			 * reserved in memory using arch_reserve_mem_area()
> +			 * below. As this particular use case only requires
> +			 * read access, fall through to the R/O mapping case.
> +			 */
> +			fallthrough;
>  
>  		case EFI_RUNTIME_SERVICES_CODE:
>  			/*
> @@ -388,3 +401,8 @@ int apei_claim_sea(struct pt_regs *regs)
>  
>  	return err;
>  }
> +
> +void arch_reserve_mem_area(acpi_physical_address addr, size_t size)
> +{
> +	memblock_mark_nomap(addr, size);
> +}
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 1e4cdc6c7ae2..64ae25c59d55 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -958,7 +958,7 @@ void acpi_os_set_prepare_extended_sleep(int (*func)(u8 sleep_state,
>  acpi_status acpi_os_prepare_extended_sleep(u8 sleep_state,
>  					   u32 val_a, u32 val_b);
>  
> -#ifdef CONFIG_X86
> +#ifndef CONFIG_IA64
>  void arch_reserve_mem_area(acpi_physical_address addr, size_t size);
>  #else
>  static inline void arch_reserve_mem_area(acpi_physical_address addr,


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