On 2/1/2017 2:08 PM, Jeffrey Hugo wrote:
On 2/1/2017 10:45 AM, Ard Biesheuvel wrote:
Some AArch64 UEFI implementations disable the MMU in ExitBootServices(),
after which unaligned accesses to RAM are no longer supported.
Commit abfb7b686a3e ("efi/libstub/arm*: Pass latest memory map to the
kernel") fixed an issue in the memory map handling of the stub FDT code,
but inadvertently created an issue with such firmwares, by moving some
of the FDT manipulation to after the invocation of ExitBootServices().
Given that the stub's libfdt implementation uses the ordinary,
accelerated
string functions, which rely on hardware handling of unaligned accesses,
manipulating the FDT with the MMU off may result in alignment faults.
So fix the situation by moving the update_fdt_memmap() call into the
callback function invoked by efi_exit_boot_services() right before it
calls the ExitBootServices() UEFI service (which is arguably a better
place for it anyway)
Note that disabling the MMU in ExitBootServices() is not compliant with
the UEFI spec, and carries great risk due to the fact that switching from
cached to uncached memory accesses halfway through compiler generated
code
(i.e., involving a stack) can never be done in a way that is
architecturally
safe.
Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: abfb7b686a3e ("efi/libstub/arm*: Pass latest memory map to the
kernel")
Tested-by: Riku Voipio <riku.voipio@xxxxxxxxxx>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
NACK, please. This causes a regression on my platform, in the form of
an assert in UEFI once ExitBootServices() is called, per initial
testing. I'll do more testing to determine why.
Sorry, false alarm. The assert appears to have been the result of a bad
tree and a bad target configuration, and was not reproduced on another
setup, nor did the assert make sense in context with this change.
I withdraw my NACK.
--
Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.
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