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Instead of relying on a dodgy dd hack to copy the image code size from
the uncompressed image's PE header to the end of the compressed image,
let's grab the code size from the symbol that is injected into the ELF
object by the Kbuild rules that generate the compressed payload.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
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We don't really care about the size of the decompressed image - what
matters is how much space needs to be allocated for the image to
execute, and this includes space for BSS that is not part of the
loadable image and so it is not accounted for in the decompressed size.
So let's add some zero padding to the end of the image: this compresses
well, and it ensures that BSS is accounted for, and as a bonus, it will
be zeroed before launching the image.
Since all architectures that implement support for EFI zboot carry this
value in the header in the same location, we can just grab it from the
binary that is being compressed.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
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In some cases, we expose the kernel's struct screen_info to the EFI stub
directly, so it gets populated before even entering the kernel. This
means the early console is available as soon as the early param parsing
happens, which is nice. It also means we need two different ways to pass
this information, as this trick only works if the EFI stub is baked into
the core kernel image, which is not always the case.
Huacai reports that the preparatory refactoring that was needed to
implement this alternative method for zboot resulted in a non-functional
efifb earlycon for other cases as well, due to the reordering of the
kernel image relocation with the population of the screen_info struct,
and the latter now takes place after copying the image to its new
location, which means we copy the old, uninitialized state.
So let's ensure that the same-image version of alloc_screen_info()
produces the correct screen_info pointer, by taking the displacement of
the loaded image into account.
Reported-by: Huacai Chen <chenhuacai@loongson.cn>
Tested-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://lore.kernel.org/linux-efi/20230310021749.921041-1-chenhuacai@loongson.cn/
Fixes: 42c8ea3dca094ab8 ("efi: libstub: Factor out EFI stub entrypoint into separate file")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
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Use the recently introduced EFI_MEMORY_ATTRIBUTES_PROTOCOL in the zboot
implementation to set the right attributes for the code and data
sections of the decompressed image, i.e., EFI_MEMORY_RO for code and
EFI_MEMORY_XP for data.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
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Even though our EFI zboot decompressor is pedantically spec compliant
and idiomatic for EFI image loaders, calling LoadImage() and
StartImage() for the nested image is a bit of a burden. Not only does it
create workflow issues for the distros (as both the inner and outer
PE/COFF images need to be signed for secure boot), it also copies the
image around in memory numerous times:
- first, the image is decompressed into a buffer;
- the buffer is consumed by LoadImage(), which copies the sections into
a newly allocated memory region to hold the executable image;
- once the EFI stub is invoked by StartImage(), it will also move the
image in memory in case of KASLR, mirrored memory or if the image must
execute from a certain a priori defined address.
There are only two EFI spec compliant ways to load code into memory and
execute it:
- use LoadImage() and StartImage(),
- call ExitBootServices() and take ownership of the entire system, after
which anything goes.
Given that the EFI zboot decompressor always invokes the EFI stub, and
given that both are built from the same set of objects, let's merge the
two, so that we can avoid LoadImage()/StartImage but still load our
image into memory without breaking the above rules.
This also means we can decompress the image directly into its final
location, which could be randomized or meet other platform specific
constraints that LoadImage() does not know how to adhere to. It also
means that, even if the encapsulated image still has the EFI stub
incorporated as well, it does not need to be signed for secure boot when
wrapping it in the EFI zboot decompressor.
In the future, we might decide to retire the EFI stub attached to the
decompressed image, but for the time being, they can happily coexist.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
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Split the efi_printk() routine into its own source file, and provide
local implementations of strlen() and strnlen() so that the standalone
zboot app can efi_err and efi_info etc.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
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We will no longer be able to call into the kernel image once we merge
the decompressor with the EFI stub, so we need our own implementation of
memcmp(). Let's add the one from lib/string.c and simplify it.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
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LoadImage() is supposed to install an instance of the protocol
EFI_LOADED_IMAGE_DEVICE_PATH_PROTOCOL onto the loaded image's handle so
that the program can figure out where it was loaded from. The reference
implementation even does this (with a NULL protocol pointer) if the call
to LoadImage() used the source buffer and size arguments, and passed
NULL for the image device path. Hand rolled implementations of LoadImage
may behave differently, though, and so it is better to tolerate
situations where the protocol is missing. And actually, concatenating an
Offset() node to a NULL device path (as we do currently) is not great
either.
So in cases where the protocol is absent, or when it points to NULL,
construct a MemoryMapped() device node as the base node that describes
the parent image's footprint in memory.
Cc: Daan De Meyer <daandemeyer@fb.com>
Cc: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
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Implement a minimal EFI app that decompresses the real kernel image and
launches it using the firmware's LoadImage and StartImage boot services.
This removes the need for any arch-specific hacks.
Note that on systems that have UEFI secure boot policies enabled,
LoadImage/StartImage require images to be signed, or their hashes known
a priori, in order to be permitted to boot.
There are various possible strategies to work around this requirement,
but they all rely either on overriding internal PI/DXE protocols (which
are not part of the EFI spec) or omitting the firmware provided
LoadImage() and StartImage() boot services, which is also undesirable,
given that they encapsulate platform specific policies related to secure
boot and measured boot, but also related to memory permissions (whether
or not and which types of heap allocations have both write and execute
permissions.)
The only generic and truly portable way around this is to simply sign
both the inner and the outer image with the same key/cert pair, so this
is what is implemented here.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
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