On Thu, Oct 13, 2022 at 06:06:48PM -0300, Guilherme G. Piccoli wrote: > By default, the efi-pstore backend hardcode the UEFI variable size > as 1024 bytes. The historical reasons for that were discussed by > Ard in threads [0][1]: > > "there is some cargo cult from prehistoric EFI times going > on here, it seems. Or maybe just misinterpretation of the maximum > size for the variable *name* vs the variable itself.". > > "OVMF has > OvmfPkg/OvmfPkgX64.dsc: > gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000 > OvmfPkg/OvmfPkgX64.dsc: > gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x8400 > > where the first one is without secure boot and the second with secure > boot. Interestingly, the default is > > gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x400 > > so this is probably where this 1k number comes from." > > With that, and since there is not such a limit in the UEFI spec, we > have the confidence to hereby add a module parameter to enable advanced > users to change the UEFI record size for efi-pstore data collection, > this way allowing a much easier reading of the collected log, which is > not scattered anymore among many small files. > > Through empirical analysis we observed that extreme low values (like 8 > bytes) could eventually cause writing issues, so given that and the OVMF > default discussed, we limited the minimum value to 1024 bytes, which also > is still the default. > > [0] https://lore.kernel.org/lkml/CAMj1kXF4UyRMh2Y_KakeNBHvkHhTtavASTAxXinDO1rhPe_wYg@xxxxxxxxxxxxxx/ > [1] https://lore.kernel.org/lkml/CAMj1kXFy-2KddGu+dgebAdU9v2sindxVoiHLWuVhqYw+R=kqng@xxxxxxxxxxxxxx/ > > Cc: Ard Biesheuvel <ardb@xxxxxxxxxx> > Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx> With the var length change recommended by Ard, yeah, looks good to me. :) Thanks! -Kees -- Kees Cook
