linux-kernel - [PATCH 5.10 88/96] efi/libstub: arm64: Double check image alignment at entry

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Message-Id: <20210816125437.920682951@linuxfoundation.org>
Date:   Mon, 16 Aug 2021 15:02:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: [PATCH 5.10 88/96] efi/libstub: arm64: Double check image alignment at entry

From: Ard Biesheuvel <ardb@...nel.org>

commit c32ac11da3f83bb42b986702a9b92f0a14ed4182 upstream.

On arm64, the stub only moves the kernel image around in memory if
needed, which is typically only for KASLR, given that relocatable
kernels (which is the default) can run from any 64k aligned address,
which is also the minimum alignment communicated to EFI via the PE/COFF
header.

Unfortunately, some loaders appear to ignore this header, and load the
kernel at some arbitrary offset in memory. We can deal with this, but
let's check for this condition anyway, so non-compliant code can be
spotted and fixed.

Cc: <stable@...r.kernel.org> # v5.10+
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
Tested-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/firmware/efi/libstub/arm64-stub.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/firmware/efi/libstub/arm64-stub.c
+++ b/drivers/firmware/efi/libstub/arm64-stub.c
@@ -119,6 +119,10 @@ efi_status_t handle_kernel_image(unsigne
 	if (image->image_base != _text)
 		efi_err("FIRMWARE BUG: efi_loaded_image_t::image_base has bogus value\n");
 
+	if (!IS_ALIGNED((u64)_text, EFI_KIMG_ALIGN))
+		efi_err("FIRMWARE BUG: kernel image not aligned on %ldk boundary\n",
+			EFI_KIMG_ALIGN >> 10);
+
 	kernel_size = _edata - _text;
 	kernel_memsize = kernel_size + (_end - _edata);
 	*reserve_size = kernel_memsize;