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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Zhang Boyang <zhangboyang.id@gmail.com>
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Date: Sun, 14 Aug 2022 15:51:54 +0800
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Subject: [PATCH] kern/efi/sb: Enforce verification of font files
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As a mitigation and hardening measure enforce verification of font
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files. Then only trusted font files can be load. This will reduce the
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attack surface at cost of losing the ability of end-users to customize
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fonts if e.g. UEFI Secure Boot is enabled. Vendors can always customize
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fonts because they have ability to pack fonts into their GRUB bundles.
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This goal is achieved by:
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* Removing GRUB_FILE_TYPE_FONT from shim lock verifier's
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skip-verification list.
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* Adding GRUB_FILE_TYPE_FONT to lockdown verifier's defer-auth list,
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so font files must be verified by a verifier before they can be loaded.
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Suggested-by: Daniel Kiper <daniel.kiper@oracle.com>
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Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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(cherry picked from commit 630deb8c0d8b02b670ced4b7030414bcf17aa080)
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(cherry picked from commit 37257e0ee45b9029b62f4046c983481d063b821d)
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---
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grub-core/kern/efi/sb.c | 1 -
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grub-core/kern/lockdown.c | 1 +
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2 files changed, 1 insertion(+), 1 deletion(-)
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diff --git a/grub-core/kern/efi/sb.c b/grub-core/kern/efi/sb.c
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index 89c4bb3fd1..db42c2539f 100644
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--- a/grub-core/kern/efi/sb.c
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+++ b/grub-core/kern/efi/sb.c
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@@ -145,7 +145,6 @@ shim_lock_verifier_init (grub_file_t io __attribute__ ((unused)),
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case GRUB_FILE_TYPE_PRINT_BLOCKLIST:
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case GRUB_FILE_TYPE_TESTLOAD:
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case GRUB_FILE_TYPE_GET_SIZE:
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- case GRUB_FILE_TYPE_FONT:
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case GRUB_FILE_TYPE_ZFS_ENCRYPTION_KEY:
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case GRUB_FILE_TYPE_CAT:
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case GRUB_FILE_TYPE_HEXCAT:
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diff --git a/grub-core/kern/lockdown.c b/grub-core/kern/lockdown.c
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index 0bc70fd42d..af6d493cd3 100644
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--- a/grub-core/kern/lockdown.c
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+++ b/grub-core/kern/lockdown.c
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@@ -51,6 +51,7 @@ lockdown_verifier_init (grub_file_t io __attribute__ ((unused)),
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case GRUB_FILE_TYPE_EFI_CHAINLOADED_IMAGE:
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case GRUB_FILE_TYPE_ACPI_TABLE:
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case GRUB_FILE_TYPE_DEVICE_TREE_IMAGE:
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+ case GRUB_FILE_TYPE_FONT:
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*flags = GRUB_VERIFY_FLAGS_DEFER_AUTH;
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/* Fall through. */
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