lkml.org 
[lkml]   [2020]   [Apr]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH 3/9] efi/x86: Move efi stub globals from .bss to .data
    On Thu, Apr 9, 2020 at 9:07 AM Ard Biesheuvel <ardb@kernel.org> wrote:
    >
    > From: Arvind Sankar <nivedita@alum.mit.edu>
    >
    > Commit
    >
    > 3ee372ccce4d ("x86/boot/compressed/64: Remove .bss/.pgtable from bzImage")
    >
    > removed the .bss section from the bzImage.
    >
    > However, while a PE loader is required to zero-initialize the .bss
    > section before calling the PE entry point, the EFI handover protocol
    > does not currently document any requirement that .bss be initialized by
    > the bootloader prior to calling the handover entry.
    >
    > When systemd-boot is used to boot a unified kernel image [1], the image
    > is constructed by embedding the bzImage as a .linux section in a PE
    > executable that contains a small stub loader from systemd together with
    > additional sections and potentially an initrd. As the .bss section
    > within the bzImage is no longer explicitly present as part of the file,
    > it is not initialized before calling the EFI handover entry.
    > Furthermore, as the size of the embedded .linux section is only the size
    > of the bzImage file itself, the .bss section's memory may not even have
    > been allocated.
    >
    > In particular, this can result in efi_disable_pci_dma being true even
    > when it was not specified via the command line or configuration option,
    > which in turn causes crashes while booting on some systems.
    >
    > To avoid issues, place all EFI stub global variables into the .data
    > section instead of .bss. As of this writing, only boolean flags for a
    > few command line arguments and the sys_table pointer were in .bss and
    > will now move into the .data section.
    >
    > [1] https://systemd.io/BOOT_LOADER_SPECIFICATION/#type-2-efi-unified-kernel-images
    >
    > Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
    > Reported-by: Sergey Shatunov <me@prok.pw>
    > Fixes: 3ee372ccce4d ("x86/boot/compressed/64: Remove .bss/.pgtable from bzImage")
    > Link: https://lore.kernel.org/r/20200406180614.429454-1-nivedita@alum.mit.edu
    > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
    > ---
    > drivers/firmware/efi/libstub/efistub.h | 2 +-
    > drivers/firmware/efi/libstub/x86-stub.c | 2 +-
    > 2 files changed, 2 insertions(+), 2 deletions(-)
    >
    > diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
    > index cc90a748bcf0..67d26949fd26 100644
    > --- a/drivers/firmware/efi/libstub/efistub.h
    > +++ b/drivers/firmware/efi/libstub/efistub.h
    > @@ -25,7 +25,7 @@
    > #define EFI_ALLOC_ALIGN EFI_PAGE_SIZE
    > #endif
    >
    > -#ifdef CONFIG_ARM
    > +#if defined(CONFIG_ARM) || defined(CONFIG_X86)
    > #define __efistub_global __section(.data)
    > #else
    > #define __efistub_global
    > diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
    > index e02ea51273ff..867a57e28980 100644
    > --- a/drivers/firmware/efi/libstub/x86-stub.c
    > +++ b/drivers/firmware/efi/libstub/x86-stub.c
    > @@ -20,7 +20,7 @@
    > /* Maximum physical address for 64-bit kernel with 4-level paging */
    > #define MAXMEM_X86_64_4LEVEL (1ull << 46)
    >
    > -static efi_system_table_t *sys_table;
    > +static efi_system_table_t *sys_table __efistub_global;
    > extern const bool efi_is64;
    > extern u32 image_offset;
    >
    > --
    > 2.17.1
    >

    Can we use the -fno-zero-initialized-in-bss compiler flag instead of
    explicitly marking global variables?

    --
    Brian Gerst

    \
     
     \ /
      Last update: 2020-04-09 22:06    [W:4.083 / U:0.040 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site