RE: [PATCH] efi/arm: fix allocation failure when reserving the kernel base

[Guillaume Gardet]

> -----Original Message-----
> From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Sent: 04 August 2019 09:57
> To: Chester Lin <clin@xxxxxxxx>; linux@xxxxxxxxxxxxxxx
> Cc: akpm@xxxxxxxxxxxxxxxxxxxx; rppt@xxxxxxxxxxxxx; ren_guo@xxxxxxxxx;
> Juergen Gross <JGross@xxxxxxxx>; geert@xxxxxxxxxxxxxx; mingo@xxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
> efi@xxxxxxxxxxxxxxx; Guillaume Gardet <Guillaume.Gardet@xxxxxxx>; Joey Lee
> <JLee@xxxxxxxx>; Gary Lin <GLin@xxxxxxxx>
> Subject: Re: [PATCH] efi/arm: fix allocation failure when reserving the kernel
> base
>
> Hello Chester,
>
> On Fri, 2 Aug 2019 at 08:40, Chester Lin <clin@xxxxxxxx> wrote:
> >
> > In some cases the arm32 efistub could fail to allocate memory for
> > uncompressed kernel. For example, we got the following error message
> > when verifying EFI stub on Raspberry Pi-2 [kernel-5.2.1 + grub-2.04] :
> >
> >   EFI stub: Booting Linux Kernel...
> >   EFI stub: ERROR: Unable to allocate memory for uncompressed kernel.
> >   EFI stub: ERROR: Failed to relocate kernel
> >
> > After checking the EFI memory map we found that the first page [0 -
> > 0xfff] had been reserved by Raspberry Pi-2's firmware, and the efistub
> > tried to set the dram base at 0, which was actually in a reserved region.
> >
>
> This by itself is a violation of the Linux boot protocol for 32-bit ARM when using
> the decompressor. The decompressor rounds down its own base address to a
> multiple of 128 MB, and assumes the whole area is available for the
> decompressed kernel and related data structures.
> (The first TEXT_OFFSET bytes are no longer used in practice, which is why putting
> a reserved region of 4 KB bytes works at the moment, but this is fragile). Note
> that the decompressor does not look at any DT or EFI provided memory maps
> *at all*.
>
> So unfortunately, this is not something we can fix in the kernel, but we should fix
> it in the bootloader or in GRUB, so it does not put any reserved regions in the
> first 128 MB of memory,

FYI, this is in Raspberry Pi firmware: https://github.com/raspberrypi/firmware/issues/1199


>
>
> >   grub> lsefimmap
> >   Type      Physical start  - end             #Pages        Size Attributes
> >   reserved  0000000000000000-0000000000000fff 00000001      4KiB WB
> >   conv-mem  0000000000001000-0000000007ef5fff 00007ef5 130004KiB WB
> >   RT-data   0000000007ef6000-0000000007f09fff 00000014     80KiB RT WB
> >   conv-mem  0000000007f0a000-000000002d871fff 00025968 615840KiB WB
> >   .....
> >
> > To avoid a reserved address, we have to ignore the memory regions
> > which are marked as EFI_RESERVED_TYPE, and only conventional memory
> > regions can be chosen. If the region before the kernel base is
> > unaligned, it will be marked as EFI_RESERVED_TYPE and let kernel
> > ignore it so that memblock_limit will not be sticked with a very low address
> such as 0x1000.
> >
> > Signed-off-by: Chester Lin <clin@xxxxxxxx>
> > ---
> >  arch/arm/mm/mmu.c                         |  3 ++
> >  drivers/firmware/efi/libstub/arm32-stub.c | 43
> > ++++++++++++++++++-----
> >  2 files changed, 37 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c index
> > f3ce34113f89..909b11ba48d8 100644
> > --- a/arch/arm/mm/mmu.c
> > +++ b/arch/arm/mm/mmu.c
> > @@ -1184,6 +1184,9 @@ void __init adjust_lowmem_bounds(void)
> >                 phys_addr_t block_start = reg->base;
> >                 phys_addr_t block_end = reg->base + reg->size;
> >
> > +               if (memblock_is_nomap(reg))
> > +                       continue;
> > +
> >                 if (reg->base < vmalloc_limit) {
> >                         if (block_end > lowmem_limit)
> >                                 /*
> > diff --git a/drivers/firmware/efi/libstub/arm32-stub.c
> > b/drivers/firmware/efi/libstub/arm32-stub.c
> > index e8f7aefb6813..10d33d36df00 100644
> > --- a/drivers/firmware/efi/libstub/arm32-stub.c
> > +++ b/drivers/firmware/efi/libstub/arm32-stub.c
> > @@ -128,7 +128,7 @@ static efi_status_t
> > reserve_kernel_base(efi_system_table_t *sys_table_arg,
> >
> >         for (l = 0; l < map_size; l += desc_size) {
> >                 efi_memory_desc_t *desc;
> > -               u64 start, end;
> > +               u64 start, end, spare, kernel_base;
> >
> >                 desc = (void *)memory_map + l;
> >                 start = desc->phys_addr; @@ -144,27 +144,52 @@ static
> > efi_status_t reserve_kernel_base(efi_system_table_t *sys_table_arg,
> >                 case EFI_BOOT_SERVICES_DATA:
> >                         /* Ignore types that are released to the OS anyway */
> >                         continue;
> > -
> > +               case EFI_RESERVED_TYPE:
> > +                       /* Ignore reserved regions */
> > +                       continue;
> >                 case EFI_CONVENTIONAL_MEMORY:
> >                         /*
> >                          * Reserve the intersection between this entry and the
> >                          * region.
> >                          */
> >                         start = max(start, (u64)dram_base);
> > -                       end = min(end, (u64)dram_base + MAX_UNCOMP_KERNEL_SIZE);
> > +                       kernel_base = round_up(start, PMD_SIZE);
> > +                       spare = kernel_base - start;
> > +                       end = min(end, kernel_base +
> > + MAX_UNCOMP_KERNEL_SIZE);
> > +
> > +                       status = efi_call_early(allocate_pages,
> > +                                       EFI_ALLOCATE_ADDRESS,
> > +                                       EFI_LOADER_DATA,
> > +                                       MAX_UNCOMP_KERNEL_SIZE / EFI_PAGE_SIZE,
> > +                                       &kernel_base);
> > +                       if (status != EFI_SUCCESS) {
> > +                               pr_efi_err(sys_table_arg,
> > +                                       "reserve_kernel_base: alloc failed.\n");
> > +                               goto out;
> > +                       }
> > +                       *reserve_addr = kernel_base;
> >
> > +                       if (!spare)
> > +                               break;
> > +                       /*
> > +                        * If there's a gap between start and kernel_base,
> > +                        * it needs be reserved so that the memblock_limit
> > +                        * will not fall on a very low address when running
> > +                        * adjust_lowmem_bounds(), wchich could eventually
> > +                        * cause CMA reservation issue.
> > +                        */
> >                         status = efi_call_early(allocate_pages,
> >                                                 EFI_ALLOCATE_ADDRESS,
> > -                                               EFI_LOADER_DATA,
> > -                                               (end - start) / EFI_PAGE_SIZE,
> > +                                               EFI_RESERVED_TYPE,
> > +                                               spare / EFI_PAGE_SIZE,
> >                                                 &start);
> >                         if (status != EFI_SUCCESS) {
> >                                 pr_efi_err(sys_table_arg,
> > -                                       "reserve_kernel_base(): alloc failed.\n");
> > +                                       "reserve spare-region
> > + failed\n");
> >                                 goto out;
> >                         }
> > -                       break;
> >
> > +                       break;
> >                 case EFI_LOADER_CODE:
> >                 case EFI_LOADER_DATA:
> >                         /*
> > @@ -220,7 +245,7 @@ efi_status_t handle_kernel_image(efi_system_table_t
> *sys_table,
> >         *image_size = image->image_size;
> >         status = efi_relocate_kernel(sys_table, image_addr, *image_size,
> >                                      *image_size,
> > -                                    dram_base + MAX_UNCOMP_KERNEL_SIZE, 0);
> > +                                    *reserve_addr +
> > + MAX_UNCOMP_KERNEL_SIZE, 0);
> >         if (status != EFI_SUCCESS) {
> >                 pr_efi_err(sys_table, "Failed to relocate kernel.\n");
> >                 efi_free(sys_table, *reserve_size, *reserve_addr); @@
> > -233,7 +258,7 @@ efi_status_t handle_kernel_image(efi_system_table_t
> *sys_table,
> >          * in memory. The kernel determines the base of DRAM from the
> >          * address at which the zImage is loaded.
> >          */
> > -       if (*image_addr + *image_size > dram_base + ZIMAGE_OFFSET_LIMIT) {
> > +       if (*image_addr + *image_size > *reserve_addr +
> > + ZIMAGE_OFFSET_LIMIT) {
> >                 pr_efi_err(sys_table, "Failed to relocate kernel, no low memory
> available.\n");
> >                 efi_free(sys_table, *reserve_size, *reserve_addr);
> >                 *reserve_size = 0;
> > --
> > 2.22.0
> >
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