Re: [PATCH v2 1/4] arm64: export memblock_reserve()d regions via /proc/iomem

[Ard Biesheuvel]

On 19 June 2018 at 08:44, AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx> wrote:
> From: James Morse <james.morse@xxxxxxx>
>
> There has been some confusion around what is necessary to prevent kexec
> overwriting important memory regions. memblock: reserve, or nomap?
> Only memblock nomap regions are reported via /proc/iomem, kexec's
> user-space doesn't know about memblock_reserve()d regions.
>
> Until commit f56ab9a5b73ca ("efi/arm: Don't mark ACPI reclaim memory
> as MEMBLOCK_NOMAP") the ACPI tables were nomap, now they are reserved
> and thus possible for kexec to overwrite with the new kernel or initrd.
> But this was always broken, as the UEFI memory map is also reserved
> and not marked as nomap.
>
> Exporting both nomap and reserved memblock types is a nuisance as
> they live in different memblock structures which we can't walk at
> the same time.
>
> Take a second walk over memblock.reserved and add new 'reserved'
> subnodes for the memblock_reserved() regions that aren't already
> described by the existing code. (e.g. Kernel Code)
>
> We use reserve_region_with_split() to find the gaps in existing named
> regions. This handles the gap between 'kernel code' and 'kernel data'
> which is memblock_reserve()d, but already partially described by
> request_standard_resources(). e.g.:
> | 80000000-dfffffff : System RAM
> |   80080000-80ffffff : Kernel code
> |   81000000-8158ffff : reserved
> |   81590000-8237efff : Kernel data
> |   a0000000-dfffffff : Crash kernel
> | e00f0000-f949ffff : System RAM
>
> reserve_region_with_split needs kzalloc() which isn't available when
> request_standard_resources() is called, use an initcall.
>
> Reported-by: Bhupesh Sharma <bhsharma@xxxxxxxxxx>
> Reported-by: Tyler Baicar <tbaicar@xxxxxxxxxxxxxx>
> Suggested-by: Akashi Takahiro <takahiro.akashi@xxxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> Fixes: d28f6df1305a ("arm64/kexec: Add core kexec support")
> CC: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> CC: Mark Rutland <mark.rutland@xxxxxxx>

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>

> ---
>  arch/arm64/kernel/setup.c | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
>
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index 30ad2f085d1f..5b4fac434c84 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -241,6 +241,44 @@ static void __init request_standard_resources(void)
>         }
>  }
>
> +static int __init reserve_memblock_reserved_regions(void)
> +{
> +       phys_addr_t start, end, roundup_end = 0;
> +       struct resource *mem, *res;
> +       u64 i;
> +
> +       for_each_reserved_mem_region(i, &start, &end) {
> +               if (end <= roundup_end)
> +                       continue; /* done already */
> +
> +               start = __pfn_to_phys(PFN_DOWN(start));
> +               end = __pfn_to_phys(PFN_UP(end)) - 1;
> +               roundup_end = end;
> +
> +               res = kzalloc(sizeof(*res), GFP_ATOMIC);
> +               if (WARN_ON(!res))
> +                       return -ENOMEM;
> +               res->start = start;
> +               res->end = end;
> +               res->name  = "reserved";
> +               res->flags = IORESOURCE_MEM;
> +
> +               mem = request_resource_conflict(&iomem_resource, res);
> +               /*
> +                * We expected memblock_reserve() regions to conflict with
> +                * memory created by request_standard_resources().
> +                */
> +               if (WARN_ON_ONCE(!mem))
> +                       continue;
> +               kfree(res);
> +
> +               reserve_region_with_split(mem, start, end, "reserved");
> +       }
> +
> +       return 0;
> +}
> +arch_initcall(reserve_memblock_reserved_regions);
> +
>  u64 __cpu_logical_map[NR_CPUS] = { [0 ... NR_CPUS-1] = INVALID_HWID };
>
>  void __init setup_arch(char **cmdline_p)
> --
> 2.17.0
>