Re: [PATCH 3/6] x86/efi: Map RAM into the identity page table for mixed mode

Borislav Petkov
2015-11-12T18:01:32Z

On Thu, Nov 12, 2015 at 03:40:20PM +0000, Matt Fleming wrote:
> We are relying on the pre-existing mappings in 'trampoline_pgd' when
> accessing function arguments in the EFI mixed mode thunking code.
>
> Instead let's map memory explicitly so that things will continue to
> work when we move to a separate page table in the future.
>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
> ---
> arch/x86/platform/efi/efi_64.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index c8b58ac47b77..634536034e32 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -144,6 +144,7 @@ void efi_sync_low_kernel_mappings(void)
> int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
> {
> unsigned long pfn, text;
> + efi_memory_desc_t *md;
> struct page *page;
> unsigned npages;
> pgd_t *pgd;
> @@ -200,6 +201,25 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
>
> efi_scratch.phys_stack += PAGE_SIZE; /* stack grows down */
>
> + /*
> + * Map all of RAM so that we can access arguments in the 1:1

Why "all of RAM"?

> + * mapping when making EFI runtime calls.
> + */
> + for_each_efi_memory_desc(&memmap, md) {
> + if (md->type != EFI_CONVENTIONAL_MEMORY &&
> + md->type != EFI_LOADER_DATA &&
> + md->type != EFI_LOADER_CODE)

That's mapping all those EFI_* types...

> + continue;
> +
> + pfn = md->phys_addr >> PAGE_SHIFT;
> + npages = md->num_pages;
> +
> + if (kernel_map_pages_in_pgd(pgd, pfn, md->phys_addr, npages, 0)) {
> + pr_err("Failed to map 1:1 memory\n");
> + return 1;
> + }
> + }
> +
> return 0;
> }
>
> --
> 2.6.2
>
>

--
Regards/Gruss,
Boris.

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