kernel/arch/arm/boot/compressed/efi-header.S, branch linux-6.2.y

ARM: 9159/1: decompressor: Avoid UNPREDICTABLE NOP encoding

2021-12-17T11:34:32Z

In the decompressor's head.S we need to start with an instruction that is some kind of NOP, but also mimics as the PE/COFF header, when the kernel is linked as an UEFI application. The clever solution here is "tstne r0, #0x4d000", which in the worst case just clobbers the condition flags, and bears the magic "MZ" signature in the lowest 16 bits. However the encoding used (0x13105a4d) is actually not valid, since bits [15:12] are supposed to be 0 (written as "(0)" in the ARM ARM). Violating this is UNPREDICTABLE, and *can* trigger an UNDEFINED exception. Common Cortex cores seem to ignore those bits, but QEMU chooses to trap, so the code goes fishing because of a missing exception handler at this point. We are just saved by the fact that commonly (with -kernel or when running from U-Boot) the "Z" bit is set, so the instruction is never executed. See [0] for more details. To make things more robust and avoid UNPREDICTABLE behaviour in the kernel code, lets replace this with a "two-instruction NOP": The first instruction is an exclusive OR, the effect of which the second instruction reverts. This does not leave any trace, neither in a register nor in the condition flags. Also it's a perfectly valid encoding. Kudos to Peter Maydell for coming up with this gem. [0] https://lore.kernel.org/qemu-devel/YTPIdbUCmwagL5%2FD@os.inf.tu-dresden.de/T/ Link: https://lore.kernel.org/linux-arm-kernel/20210908162617.104962-1-andre.przywara@arm.com/T/ Fixes: 81a0bc39ea19 ("ARM: add UEFI stub support") Signed-off-by: Andre Przywara Reported-by: Adam Lackorzynski Suggested-by: Peter Maydell Reviewed-by: Ard Biesheuvel Reviewed-by: Linus Walleij Signed-off-by: Russell King (Oracle)

efi/libstub: Add missing prototype for PE/COFF entry point

2020-05-23T09:01:57Z

Fix a missing prototype warning by adding a forward declaration for the PE/COFF entrypoint, and while at it, align the function name between the x86 and ARM versions of the stub. Signed-off-by: Ard Biesheuvel

efi/libstub: Introduce symbolic constants for the stub major/minor version

2020-02-23T20:59:42Z

Now that we have added new ways to load the initrd or the mixed mode kernel, we will also need a way to tell the loader about this. Add symbolic constants for the PE/COFF major/minor version numbers (which fortunately have always been 0x0 for all architectures), so that we can bump them later to document the capabilities of the stub. Signed-off-by: Ard Biesheuvel

efi/libstub/arm: Make efi_entry() an ordinary PE/COFF entrypoint

2020-02-22T22:37:37Z

Expose efi_entry() as the PE/COFF entrypoint directly, instead of jumping into a wrapper that fiddles with stack buffers and other stuff that the compiler is much better at. The only reason this code exists is to obtain a pointer to the base of the image, but we can get the same value from the loaded_image protocol, which we already need for other reasons anyway. Update the return type as well, to make it consistent with what is required for a PE/COFF executable entrypoint. Signed-off-by: Ard Biesheuvel

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500

2019-06-19T15:09:55Z

Based on 2 normalized pattern(s): this program is free software you can redistribute it and or modify it under the terms of the gnu general public license version 2 as published by the free software foundation this program is free software you can redistribute it and or modify it under the terms of the gnu general public license version 2 as published by the free software foundation # extracted by the scancode license scanner the SPDX license identifier GPL-2.0-only has been chosen to replace the boilerplate/reference in 4122 file(s). Signed-off-by: Thomas Gleixner Reviewed-by: Enrico Weigelt Reviewed-by: Kate Stewart Reviewed-by: Allison Randal Cc: linux-spdx@vger.kernel.org Link: https://lkml.kernel.org/r/20190604081206.933168790@linutronix.de Signed-off-by: Greg Kroah-Hartman

arm/efi: Split zImage code and data into separate PE/COFF sections

2017-08-21T07:43:51Z

To prevent unintended modifications to the kernel text (malicious or otherwise) while running the EFI stub, describe the kernel image as two separate sections: a .text section with read-execute permissions, covering .text, .rodata, .piggytext and the GOT sections (which the stub does not care about anyway), and a .data section with read-write permissions, covering .data and .bss. This relies on the firmware to actually take the section permission flags into account, but this is something that is currently being implemented in EDK2, which means we will likely start seeing it in the wild between one and two years from now. Signed-off-by: Ard Biesheuvel Cc: Linus Torvalds Cc: Matt Fleming Cc: Peter Zijlstra Cc: Russell King Cc: Thomas Gleixner Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/20170818194947.19347-12-ard.biesheuvel@linaro.org Signed-off-by: Ingo Molnar

arm/efi: Replace open coded constants with symbolic ones

2017-08-21T07:43:50Z

Replace the various open coded constants in the EFI PE/COFF header with definitions from pe.h, or expressions based on local symbols. Signed-off-by: Ard Biesheuvel Cc: Linus Torvalds Cc: Matt Fleming Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/20170818194947.19347-11-ard.biesheuvel@linaro.org Signed-off-by: Ingo Molnar

arm/efi: Remove pointless dummy .reloc section

2017-08-21T07:43:50Z

The kernel's EFI PE/COFF header contains a dummy .reloc section, and an explanatory comment that claims that this is required for the EFI application loader to accept the Image as a relocatable image (i.e., one that can be loaded at any offset and fixed up in place) This was inherited from the x86 implementation, which has elaborate host tooling to mangle the PE/COFF header post-link time, and which populates the .reloc section with a single dummy base relocation. On ARM, no such tooling exists, and the .reloc section remains empty, and is never even exposed via the BaseRelocationTable directory entry, which is where the PE/COFF loader looks for it. The PE/COFF spec is unclear about relocatable images that do not require any fixups, but the EDK2 implementation, which is the de facto reference for PE/COFF in the UEFI space, clearly does not care, and explicitly mentions (in a comment) that relocatable images with no base relocations are perfectly fine, as long as they don't have the RELOCS_STRIPPED attribute set (which is not the case for our PE/COFF image) So simply remove the .reloc section altogether. Signed-off-by: Ard Biesheuvel Cc: Linus Torvalds Cc: Matt Fleming Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/20170818194947.19347-10-ard.biesheuvel@linaro.org Signed-off-by: Ingo Molnar

arm/efi: Remove forbidden values from the PE/COFF header

2017-08-21T07:43:50Z

Bring the PE/COFF header in line with the PE/COFF spec, by setting NumberOfSymbols to 0, and removing the section alignment flags. Signed-off-by: Ard Biesheuvel Cc: Linus Torvalds Cc: Matt Fleming Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/20170818194947.19347-9-ard.biesheuvel@linaro.org Signed-off-by: Ingo Molnar

ARM: 8680/1: boot/compressed: fix inappropriate Thumb2 mnemonic for __nop

2017-06-12T14:47:27Z

Commit 06a4b6d009a1 ("ARM: 8677/1: boot/compressed: fix decompressor header layout for v7-M") fixed an issue in the layout of the header of the compressed kernel image that was caused by the assembler emitting narrow opcodes for 'mov r0, r0', and for this reason, the mnemonic was updated to use the W() macro, which will append the .w suffix (which forces a wide encoding) if required, i.e., when building the kernel in Thumb2 mode. However, this failed to take into account that on Thumb2 kernels built for CPUs that are also ARM capable, the entry point is entered in ARM mode, and so the instructions emitted here will be ARM instructions that only exist in a wide encoding to begin with, which is why the assembler rejects the .w suffix here and aborts the build with the following message: head.S: Assembler messages: head.S:132: Error: width suffixes are invalid in ARM mode -- `mov.w r0,r0' So replace the W(mov) with separate ARM and Thumb2 instructions, where the latter will only be used for THUMB2_ONLY builds. Fixes: 06a4b6d009a1 ("ARM: 8677/1: boot/compressed: fix decompressor ...") Reported-by: Arnd Bergmann Acked-by: Arnd Bergmann Signed-off-by: Ard Biesheuvel Signed-off-by: Russell King