Re: [PATCH] efi/memreserve: deal with memreserve entries in unmapped memory

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On 06/10/2019 08:05 AM, Ard Biesheuvel wrote:
> Ensure that the EFI memreserve entries can be accessed, even if they
> are located in memory that the kernel (e.g., a crashkernel) omits from
> the linear map.
> 
> Reported-by: Jonathan Richardson <jonathan.richardson@xxxxxxxxxxxx>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> ---
>  drivers/firmware/efi/efi.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 16b2137d117c..4b7cf7bc0ded 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -1009,14 +1009,16 @@ int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
>  
>  	/* first try to find a slot in an existing linked list entry */
>  	for (prsv = efi_memreserve_root->next; prsv; prsv = rsv->next) {
> -		rsv = __va(prsv);
> +		rsv = memremap(prsv, sizeof(*rsv), MEMREMAP_WB);
>  		index = atomic_fetch_add_unless(&rsv->count, 1, rsv->size);
>  		if (index < rsv->size) {
>  			rsv->entry[index].base = addr;
>  			rsv->entry[index].size = size;
>  
> +			memunmap(rsv);
>  			return 0;
>  		}
> +		memunmap(rsv);
>  	}
>  
>  	/* no slot found - allocate a new linked list entry */
> @@ -1024,7 +1026,13 @@ int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
>  	if (!rsv)
>  		return -ENOMEM;
>  
> -	rsv->size = EFI_MEMRESERVE_COUNT(PAGE_SIZE);
> +	/*
> +	 * The memremap() call above assumes that a linux_efi_memreserve entry
> +	 * never crosses a page boundary, so let's ensure that this remains true
> +	 * even when kexec'ing a 4k pages kernel from a >4k pages kernel, by
> +	 * using SZ_4K explicitly in the size calculation below.
> +	 */
> +	rsv->size = EFI_MEMRESERVE_COUNT(SZ_4K);
>  	atomic_set(&rsv->count, 1);
>  	rsv->entry[0].base = addr;
>  	rsv->entry[0].size = size;
> 

Thanks for the fix. Tested and reviewed.

Reviewed-by: Jonathan Richardson <jonathan.richardson@xxxxxxxxxxxx>



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