On Thu, 2014-07-31 at 16:11 +0200, Ard Biesheuvel wrote:
> There are 2 interesting pieces of information in the UEFI spec section 2.3.6
> regarding the mapping of runtime regions:
> (a) the firmware should not request a virtual mapping for configuration tables,
> even though they are marked as EfiRuntimeServicesData;
> (b) calling SetVirtualAddressMap() is optional, and it is equally appropriate to
> call Runtime Services using an identity mapping.
>
> So we can eliminate some of the complexity around UEFI Runtime Services by not
> using a virtual mapping at all, and calling the services at their physical
> address. This is especially useful under kexec, as SetVirtualAddressMap() may
> only be called once, and there is no guarantee that mappings are stable between
> different kexec'd kernels.
>
> The fallout for other in-kernel users of UEFI data structures should be
> negligible, as they cannot legally access those data structures through
> pre-existing virtual mappings anyway (point (a) above)
>
> It should also be noted that, as the kernel side of the address space (TTBR1) is
> retained, the stack and pointer function arguments remain accessible to the
> runtime service while the id mapping is active.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> ---
> arch/arm64/include/asm/efi.h | 24 ++++++++--
> arch/arm64/kernel/efi.c | 106 ++-----------------------------------------
> 2 files changed, 23 insertions(+), 107 deletions(-)
>
> diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
> index a34fd3b12e2b..d42a21e79b39 100644
> --- a/arch/arm64/include/asm/efi.h
> +++ b/arch/arm64/include/asm/efi.h
> @@ -1,8 +1,10 @@
> #ifndef _ASM_EFI_H
> #define _ASM_EFI_H
>
> +#include <asm/cacheflush.h>
> #include <asm/io.h>
> #include <asm/neon.h>
> +#include <asm/tlbflush.h>
>
> #ifdef CONFIG_EFI
> extern void efi_init(void);
> @@ -12,23 +14,37 @@ extern void efi_idmap_init(void);
> #define efi_idmap_init()
> #endif
>
> +static inline void switch_pgd(pgd_t *pgd, struct mm_struct *mm)
> +{
> + cpu_switch_mm(pgd, mm);
> + flush_tlb_all();
> + if (icache_is_aivivt())
> + __flush_icache_all();
> +}
> +
> #define efi_call_virt(f, ...) \
> ({ \
> - efi_##f##_t *__f = efi.systab->runtime->f; \
> + efi_##f##_t *__f; \
> efi_status_t __s; \
> \
> - kernel_neon_begin(); \
> + kernel_neon_begin(); /* disables preemption */ \
> + switch_pgd(idmap_pg_dir, &init_mm); \
> + __f = efi.systab->runtime->f; \
> __s = __f(__VA_ARGS__); \
> + switch_pgd(current->active_mm->pgd, current->active_mm); \
> kernel_neon_end(); \
> __s; \
> })
>
> #define __efi_call_virt(f, ...) \
> ({ \
> - efi_##f##_t *__f = efi.systab->runtime->f; \
> + efi_##f##_t *__f; \
> \
> - kernel_neon_begin(); \
> + kernel_neon_begin(); /* disables preemption */ \
> + switch_pgd(idmap_pg_dir, &init_mm); \
> + __f = efi.systab->runtime->f; \
> __f(__VA_ARGS__); \
> + switch_pgd(current->active_mm->pgd, current->active_mm); \
> kernel_neon_end(); \
> })
If you replace the current user pgd with idmap pgd and there is
an exception in the firmware which would lead to the user task
being killed, what happens?
>
> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
> index e72f3100958f..d620a031e7bf 100644
> --- a/arch/arm64/kernel/efi.c
> +++ b/arch/arm64/kernel/efi.c
> @@ -27,8 +27,6 @@
>
> struct efi_memory_map memmap;
>
> -static efi_runtime_services_t *runtime;
> -
> static u64 efi_system_table;
>
> static int uefi_debug __initdata;
> @@ -340,51 +338,9 @@ void __init efi_idmap_init(void)
> efi_setup_idmap();
> }
>
> -static int __init remap_region(efi_memory_desc_t *md, void **new)
> -{
> - u64 paddr, vaddr, npages, size;
> -
> - paddr = md->phys_addr;
> - npages = md->num_pages;
> - memrange_efi_to_native(&paddr, &npages);
> - size = npages << PAGE_SHIFT;
> -
> - if (is_normal_ram(md))
> - vaddr = (__force u64)ioremap_cache(paddr, size);
> - else
> - vaddr = (__force u64)ioremap(paddr, size);
> -
> - if (!vaddr) {
> - pr_err("Unable to remap 0x%llx pages @ %p\n",
> - npages, (void *)paddr);
> - return 0;
> - }
> -
> - /* adjust for any rounding when EFI and system pagesize differs */
> - md->virt_addr = vaddr + (md->phys_addr - paddr);
> -
> - if (uefi_debug)
> - pr_info(" EFI remap 0x%012llx => %p\n",
> - md->phys_addr, (void *)md->virt_addr);
> -
> - memcpy(*new, md, memmap.desc_size);
> - *new += memmap.desc_size;
> -
> - return 1;
> -}
> -
> -/*
> - * Switch UEFI from an identity map to a kernel virtual map
> - */
> static int __init arm64_enter_virtual_mode(void)
> {
> - efi_memory_desc_t *md;
> - phys_addr_t virtmap_phys;
> - void *virtmap, *virt_md;
> - efi_status_t status;
> u64 mapsize;
> - int count = 0;
> - unsigned long flags;
>
> if (!efi_enabled(EFI_BOOT)) {
> pr_info("EFI services will not be available.\n");
> @@ -402,76 +358,20 @@ static int __init arm64_enter_virtual_mode(void)
>
> efi.memmap = &memmap;
>
> - /* Map the runtime regions */
> - virtmap = kmalloc(mapsize, GFP_KERNEL);
> - if (!virtmap) {
> - pr_err("Failed to allocate EFI virtual memmap\n");
> - return -1;
> - }
> - virtmap_phys = virt_to_phys(virtmap);
> - virt_md = virtmap;
> -
> - for_each_efi_memory_desc(&memmap, md) {
> - if (!(md->attribute & EFI_MEMORY_RUNTIME))
> - continue;
> - if (!remap_region(md, &virt_md))
> - goto err_unmap;
> - ++count;
> - }
> -
> - efi.systab = (__force void *)efi_lookup_mapped_addr(efi_system_table);
> + efi.systab = (__force void *)ioremap_cache(efi_system_table,
> + sizeof(efi_system_table_t));
> if (!efi.systab) {
> - /*
> - * If we have no virtual mapping for the System Table at this
> - * point, the memory map doesn't cover the physical offset where
> - * it resides. This means the System Table will be inaccessible
> - * to Runtime Services themselves once the virtual mapping is
> - * installed.
> - */
> pr_err("Failed to remap EFI System Table -- buggy firmware?\n");
> - goto err_unmap;
> + return -1;
> }
> set_bit(EFI_SYSTEM_TABLES, &efi.flags);
>
> - local_irq_save(flags);
> - cpu_switch_mm(idmap_pg_dir, &init_mm);
> -
> - /* Call SetVirtualAddressMap with the physical address of the map */
> - runtime = efi.systab->runtime;
> - efi.set_virtual_address_map = runtime->set_virtual_address_map;
> -
> - status = efi.set_virtual_address_map(count * memmap.desc_size,
> - memmap.desc_size,
> - memmap.desc_version,
> - (efi_memory_desc_t *)virtmap_phys);
> - cpu_set_reserved_ttbr0();
> - flush_tlb_all();
> - local_irq_restore(flags);
> -
> - kfree(virtmap);
> -
> free_boot_services();
>
> - if (status != EFI_SUCCESS) {
> - pr_err("Failed to set EFI virtual address map! [%lx]\n",
> - status);
> - return -1;
> - }
> -
> /* Set up runtime services function pointers */
> - runtime = efi.systab->runtime;
> efi_native_runtime_setup();
> set_bit(EFI_RUNTIME_SERVICES, &efi.flags);
>
> return 0;
> -
> -err_unmap:
> - /* unmap all mappings that succeeded: there are 'count' of those */
> - for (virt_md = virtmap; count--; virt_md += memmap.desc_size) {
> - md = virt_md;
> - iounmap((__force void __iomem *)md->virt_addr);
> - }
> - kfree(virtmap);
> - return -1;
> }
> early_initcall(arm64_enter_virtual_mode);
--
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