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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Dimitri John Ledkov <xnox@ubuntu.com>
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Date: Wed, 22 Jul 2020 11:31:43 +0100
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Subject: [PATCH] linuxefi: fail kernel validation without shim protocol.
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If certificates that signed grub are installed into db, grub can be
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booted directly. It will then boot any kernel without signature
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validation. The booted kernel will think it was booted in secureboot
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mode and will implement lockdown, yet it could have been tampered.
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This version of the patch skips calling verification, when booted
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without secureboot. And is indented with gnu ident.
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CVE-2020-15705
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Reported-by: Mathieu Trudel-Lapierre <cyphermox@ubuntu.com>
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Signed-off-by: Dimitri John Ledkov <xnox@ubuntu.com>
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---
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grub-core/loader/arm64/linux.c | 12 ++++++++----
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grub-core/loader/efi/chainloader.c | 1 +
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grub-core/loader/efi/linux.c | 1 +
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grub-core/loader/i386/efi/linux.c | 13 ++++++++-----
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4 files changed, 18 insertions(+), 9 deletions(-)
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diff --git a/grub-core/loader/arm64/linux.c b/grub-core/loader/arm64/linux.c
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index e1110749e..7a076c131 100644
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--- a/grub-core/loader/arm64/linux.c
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+++ b/grub-core/loader/arm64/linux.c
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@@ -381,11 +381,15 @@ grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)),
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grub_dprintf ("linux", "kernel @ %p\n", kernel_addr);
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- rc = grub_linuxefi_secure_validate (kernel_addr, kernel_size);
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- if (rc < 0)
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+ if (grub_efi_secure_boot ())
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{
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- grub_error (GRUB_ERR_INVALID_COMMAND, N_("%s has invalid signature"), argv[0]);
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- goto fail;
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+ rc = grub_linuxefi_secure_validate (kernel_addr, kernel_size);
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+ if (rc <= 0)
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+ {
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+ grub_error (GRUB_ERR_INVALID_COMMAND,
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+ N_("%s has invalid signature"), argv[0]);
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+ goto fail;
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+ }
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}
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pe = (void *)((unsigned long)kernel_addr + lh.hdr_offset);
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diff --git a/grub-core/loader/efi/chainloader.c b/grub-core/loader/efi/chainloader.c
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index 8b99cf23e..a93edc975 100644
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--- a/grub-core/loader/efi/chainloader.c
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+++ b/grub-core/loader/efi/chainloader.c
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@@ -1079,6 +1079,7 @@ grub_cmd_chainloader (grub_command_t cmd __attribute__ ((unused)),
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return 0;
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}
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+ // -1 fall-through to fail
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fail:
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if (dev)
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diff --git a/grub-core/loader/efi/linux.c b/grub-core/loader/efi/linux.c
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index e09f82486..927d89a90 100644
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--- a/grub-core/loader/efi/linux.c
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+++ b/grub-core/loader/efi/linux.c
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@@ -33,6 +33,7 @@ struct grub_efi_shim_lock
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};
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typedef struct grub_efi_shim_lock grub_efi_shim_lock_t;
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+// Returns 1 on success, -1 on error, 0 when not available
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int
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grub_linuxefi_secure_validate (void *data, grub_uint32_t size)
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{
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diff --git a/grub-core/loader/i386/efi/linux.c b/grub-core/loader/i386/efi/linux.c
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index ade7ab8f5..361e503cb 100644
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--- a/grub-core/loader/i386/efi/linux.c
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+++ b/grub-core/loader/i386/efi/linux.c
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@@ -206,12 +206,15 @@ grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)),
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grub_tpm_measure (kernel, filelen, GRUB_BINARY_PCR, "grub_linuxefi", "Kernel");
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grub_print_error();
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- rc = grub_linuxefi_secure_validate (kernel, filelen);
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- if (rc < 0)
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+ if (grub_efi_secure_boot ())
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{
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- grub_error (GRUB_ERR_INVALID_COMMAND, N_("%s has invalid signature"),
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- argv[0]);
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- goto fail;
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+ rc = grub_linuxefi_secure_validate (kernel, filelen);
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+ if (rc <= 0)
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+ {
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+ grub_error (GRUB_ERR_INVALID_COMMAND,
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+ N_("%s has invalid signature"), argv[0]);
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+ goto fail;
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+ }
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}
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params = grub_efi_allocate_pages_max (0x3fffffff,
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