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    Modify UEFI anti-bricking code · f8b84043
    Matthew Garrett 提交于
    This patch reworks the UEFI anti-bricking code, including an effective
    reversion of cc5a080c and 31ff2f20. It turns out that calling
    QueryVariableInfo() from boot services results in some firmware
    implementations jumping to physical addresses even after entering virtual
    mode, so until we have 1:1 mappings for UEFI runtime space this isn't
    going to work so well.
    
    Reverting these gets us back to the situation where we'd refuse to create
    variables on some systems because they classify deleted variables as "used"
    until the firmware triggers a garbage collection run, which they won't do
    until they reach a lower threshold. This results in it being impossible to
    install a bootloader, which is unhelpful.
    
    Feedback from Samsung indicates that the firmware doesn't need more than
    5KB of storage space for its own purposes, so that seems like a reasonable
    threshold. However, there's still no guarantee that a platform will attempt
    garbage collection merely because it drops below this threshold. It seems
    that this is often only triggered if an attempt to write generates a
    genuine EFI_OUT_OF_RESOURCES error. We can force that by attempting to
    create a variable larger than the remaining space. This should fail, but if
    it somehow succeeds we can then immediately delete it.
    
    I've tested this on the UEFI machines I have available, but I don't have
    a Samsung and so can't verify that it avoids the bricking problem.
    Signed-off-by: NMatthew Garrett <matthew.garrett@nebula.com>
    Signed-off-by: Lee, Chun-Y <jlee@suse.com> [ dummy variable cleanup ]
    Cc: <stable@vger.kernel.org>
    Signed-off-by: NMatt Fleming <matt.fleming@intel.com>
    f8b84043
eboot.c 28.8 KB