linux-kernel - [PATCH 5.19 048/207] efi: x86: Wipe setup

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Message-Id: <20220926100808.760413331@linuxfoundation.org>
Date:   Mon, 26 Sep 2022 12:10:37 +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>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH 5.19 048/207] efi: x86: Wipe setup_data on pure EFI boot

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

commit 63bf28ceb3ebbe76048c3fb2987996ca1ae64f83 upstream.

When booting the x86 kernel via EFI using the LoadImage/StartImage boot
services [as opposed to the deprecated EFI handover protocol], the setup
header is taken from the image directly, and given that EFI's LoadImage
has no Linux/x86 specific knowledge regarding struct bootparams or
struct setup_header, any absolute addresses in the setup header must
originate from the file and not from a prior loading stage.

Since we cannot generally predict where LoadImage() decides to load an
image (*), such absolute addresses must be treated as suspect: even if a
prior boot stage intended to make them point somewhere inside the
[signed] image, there is no way to validate that, and if they point at
an arbitrary location in memory, the setup_data nodes will not be
covered by any signatures or TPM measurements either, and could be made
to contain an arbitrary sequence of SETUP_xxx nodes, which could
interfere quite badly with the early x86 boot sequence.

(*) Note that, while LoadImage() does take a buffer/size tuple in
addition to a device path, which can be used to provide the image
contents directly, it will re-allocate such images, as the memory
footprint of an image is generally larger than the PE/COFF file
representation.

Cc: <stable@...r.kernel.org> # v5.10+
Link: https://lore.kernel.org/all/20220904165321.1140894-1-Jason@zx2c4.com/
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
Acked-by: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/firmware/efi/libstub/x86-stub.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -517,6 +517,13 @@ efi_status_t __efiapi efi_pe_entry(efi_h
 	hdr->ramdisk_image = 0;
 	hdr->ramdisk_size = 0;

+	/*
+	 * Disregard any setup data that was provided by the bootloader:
+	 * setup_data could be pointing anywhere, and we have no way of
+	 * authenticating or validating the payload.
+	 */
+	hdr->setup_data = 0;
+
 	efi_stub_entry(handle, sys_table_arg, boot_params);
 	/* not reached */