From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Dimitri John Ledkov Date: Wed, 22 Jul 2020 11:31:43 +0100 Subject: [PATCH] linuxefi: fail kernel validation without shim protocol. If certificates that signed grub are installed into db, grub can be booted directly. It will then boot any kernel without signature validation. The booted kernel will think it was booted in secureboot mode and will implement lockdown, yet it could have been tampered. This version of the patch skips calling verification, when booted without secureboot. And is indented with gnu ident. CVE-2020-15705 Reported-by: Mathieu Trudel-Lapierre Signed-off-by: Dimitri John Ledkov --- grub-core/loader/efi/chainloader.c | 1 + grub-core/loader/efi/linux.c | 1 + grub-core/loader/i386/efi/linux.c | 17 +++++++++++------ 3 files changed, 13 insertions(+), 6 deletions(-) diff --git a/grub-core/loader/efi/chainloader.c b/grub-core/loader/efi/chainloader.c index e4ac39c87b4..0ec682e2988 100644 --- a/grub-core/loader/efi/chainloader.c +++ b/grub-core/loader/efi/chainloader.c @@ -1088,6 +1088,7 @@ grub_cmd_chainloader (grub_command_t cmd __attribute__ ((unused)), return 0; } + // -1 fall-through to fail fail: diff --git a/grub-core/loader/efi/linux.c b/grub-core/loader/efi/linux.c index 32766bf7b19..ecb6d593cef 100644 --- a/grub-core/loader/efi/linux.c +++ b/grub-core/loader/efi/linux.c @@ -98,6 +98,7 @@ struct grub_efi_shim_lock }; typedef struct grub_efi_shim_lock grub_efi_shim_lock_t; +// Returns 1 on success, -1 on error, 0 when not available int grub_linuxefi_secure_validate (void *data, grub_uint32_t size) { diff --git a/grub-core/loader/i386/efi/linux.c b/grub-core/loader/i386/efi/linux.c index 325aa594db1..97484bbe24d 100644 --- a/grub-core/loader/i386/efi/linux.c +++ b/grub-core/loader/i386/efi/linux.c @@ -30,6 +30,7 @@ #include #include #include +#include GRUB_MOD_LICENSE ("GPLv3+"); @@ -101,7 +102,7 @@ kernel_alloc(grub_efi_uintn_t size, const char * const errmsg) pages = BYTES_TO_PAGES(size); grub_dprintf ("linux", "Trying to allocate %lu pages from %p\n", - pages, (void *)max); + (unsigned long)pages, (void *)(unsigned long)max); prev_max = max; addr = grub_efi_allocate_pages_real (max, pages, @@ -307,12 +308,15 @@ grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)), goto fail; } - rc = grub_linuxefi_secure_validate (kernel, filelen); - if (rc < 0) + if (grub_efi_get_secureboot () == GRUB_EFI_SECUREBOOT_MODE_ENABLED) { - grub_error (GRUB_ERR_INVALID_COMMAND, N_("%s has invalid signature"), - argv[0]); - goto fail; + rc = grub_linuxefi_secure_validate (kernel, filelen); + if (rc <= 0) + { + grub_error (GRUB_ERR_INVALID_COMMAND, + N_("%s has invalid signature"), argv[0]); + goto fail; + } } lh = (struct linux_i386_kernel_header *)kernel; @@ -386,6 +390,7 @@ grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)), setup_header_end_offset = *((grub_uint8_t *)kernel + 0x201); grub_dprintf ("linux", "copying %lu bytes from %p to %p\n", + (unsigned long) MIN((grub_size_t)0x202+setup_header_end_offset, sizeof (*params)) - 0x1f1, (grub_uint8_t *)kernel + 0x1f1,