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 <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170818194947.19347-12-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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 <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170818194947.19347-11-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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 <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170818194947.19347-10-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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 <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170818194947.19347-9-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Commit 06a4b6d009 ("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: 06a4b6d009 ("ARM: 8677/1: boot/compressed: fix decompressor ...")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
As reported by Patrice, the header layout of the decompressor is
incorrect when building for v7-M. In this case, the __nop macro
resolves to 'mov r0, r0', which is emitted as a narrow encoding,
resulting in the header data fields to end up at lower offsets than
required.
Given the variety of targets we need to support with the same code,
the startup sequence is a bit of a jumble, and uses instructions
and macros whose encoding widths cannot be specified (badr), or only
exist in a narrow encoding (bx)
So force the use of a wide encoding in __nop, and replace the start
sequence with a simple jump to the label marking the start of code,
preceded by a Thumb2 mode switch if required (using explicit wide
encodings where appropriate). The label itself can be moved to the
start of code [where it belongs] due to the larger range of branch
instructions as compared to adr instructions.
Reported-by: Patrice CHOTARD <patrice.chotard@st.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
This patch adds EFI stub support for the ARM Linux kernel.
The EFI stub operates similarly to the x86 and arm64 stubs: it is a
shim between the EFI firmware and the normal zImage entry point, and
sets up the environment that the zImage is expecting. This includes
optionally loading the initrd and device tree from the system partition
based on the kernel command line.
Signed-off-by: Roy Franz <roy.franz@linaro.org>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
