linux-kernel - Re: [PATCH v4 3/4] efi: Fix efi_memmap

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Date:   Tue, 7 Jan 2020 11:58:24 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     mingo@...hat.com, Taku Izumi <izumi.taku@...fujitsu.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-efi@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, kexec@...ts.infradead.org
Subject: Re: [PATCH v4 3/4] efi: Fix efi_memmap_alloc() leaks

On 01/06/20 at 04:40pm, Dan Williams wrote:
> With efi_fake_memmap() and efi_arch_mem_reserve() the efi table may be
> updated and replaced multiple times. When that happens a previous
> dynamically allocated efi memory map can be garbage collected. Use the
> new EFI_MEMMAP_{SLAB,MEMBLOCK} flags to detect when a dynamically
> allocated memory map is being replaced.
> 
> Debug statements in efi_memmap_free() reveal:
> 
>  efi: __efi_memmap_free:37: phys: 0x23ffdd580 size: 2688 flags: 0x2
>  efi: __efi_memmap_free:37: phys: 0x9db00 size: 2640 flags: 0x2
>  efi: __efi_memmap_free:37: phys: 0x9e580 size: 2640 flags: 0x2
> 
> ...a savings of 7968 bytes on a qemu boot with 2 entries specified to
> efi_fake_mem=.
> 
> Cc: Taku Izumi <izumi.taku@...fujitsu.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>  drivers/firmware/efi/memmap.c |   24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/firmware/efi/memmap.c b/drivers/firmware/efi/memmap.c
> index 04dfa56b994b..bffa320d2f9a 100644
> --- a/drivers/firmware/efi/memmap.c
> +++ b/drivers/firmware/efi/memmap.c
> @@ -29,6 +29,28 @@ static phys_addr_t __init __efi_memmap_alloc_late(unsigned long size)
>  	return PFN_PHYS(page_to_pfn(p));
>  }
>  
> +static void __init __efi_memmap_free(u64 phys, unsigned long size, unsigned long flags)
> +{
> +	if (flags & EFI_MEMMAP_MEMBLOCK) {
> +		if (slab_is_available())
> +			memblock_free_late(phys, size);
> +		else
> +			memblock_free(phys, size);
> +	} else if (flags & EFI_MEMMAP_SLAB) {
> +		struct page *p = pfn_to_page(PHYS_PFN(phys));
> +		unsigned int order = get_order(size);
> +
> +		free_pages((unsigned long) page_address(p), order);
> +	}
> +}
> +
> +static void __init efi_memmap_free(void)
> +{
> +	__efi_memmap_free(efi.memmap.phys_map,
> +			efi.memmap.desc_size * efi.memmap.nr_map,
> +			efi.memmap.flags);
> +}
> +
>  /**
>   * efi_memmap_alloc - Allocate memory for the EFI memory map
>   * @num_entries: Number of entries in the allocated map.
> @@ -100,6 +122,8 @@ static int __init __efi_memmap_init(struct efi_memory_map_data *data)
>  		return -ENOMEM;
>  	}
>  
> +	efi_memmap_free();
> +

This seems still not safe,  see below function:
arch/x86/platform/efi/efi.c:
static void __init efi_clean_memmap(void)
It use same memmap for both old and new, and filter out those invalid
ranges in place, if the memory is freed then ..

>  	map.phys_map = data->phys_map;
>  	map.nr_map = data->size / data->desc_size;
>  	map.map_end = map.map + data->size;
> 

Thanks
Dave