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Linux 6.7 Reworks PE Header Technology To Cut back Assault Space

Linux 6.7 Reworks PE Header Technology To Cut back Assault Space

2023-10-29 16:10:52


One of many many early pull requests despatched in for Linux 6.7 have been the x86/boot modifications which are headlined by a rework to the PE header era to be able to generate a contemporary, 4K-aligned kernel picture view to in the end intention for higher system safety.

Ard Biesheuvel led the trouble on this PE header era rework. He defined within the patch sequence final month:

“Now that the EFI stub boot circulate now not depends on reminiscence that’s executable and writable on the similar time, we will reorganize the PE/COFF view of the kernel picture and expose the decompressor binary’s code and r/o knowledge as a .textual content part and knowledge/bss as a .knowledge part, utilizing 4k alignment and restricted permissions.

Doing so is important for compatibility with hardening measures which are being rolled out on x86 PCs constructed to run Home windows (i.e., nearly all of them). The EFI boot atmosphere that the Linux EFI stub executes in is very delicate to issues of safety, given {that a} vulnerability within the loader of 1 OS could be abused to assault one other.

In true x86 trend, this can be a lot extra difficult than on different architectures, which have carried out this code/knowledge cut up with 4k alignment from the start. The complicating issue right here is that the boot picture consists of two totally different components, that are stitched collectively and stuck up utilizing a particular construct software.

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After this sequence is utilized, the one remaining activity carried out by the construct software is producing the CRC-32. Regardless that this checksum is normally improper (provided that distro kernels are signed for safe boot in a method that corrupts the CRC), this characteristic is retained as we can’t make certain that no one is counting on this.

This supersedes the work proposed by Evgeniy final yr, which did a significant rewrite of the construct software to be able to clear it up, earlier than updating it to generate the brand new 4k aligned picture structure. As this sequence proves, the construct software is usually pointless, and we now have too a lot of these already.”

This work is the principle spotlight of the x86/boot changes submitted for the Linux 6.7 merge window.

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