[d-kernel] [PATCH v2 5/6] efi: determine and pass Secure Boot state via FDT

[Egor Ignatov <egori@altlinux.org>]

From: Linn Crosetto <linn@hpe.com>

Determine the state of UEFI Secure Boot in the EFI stub on platforms
that use FDT-based EFI parameter passing (ARM, arm64, RISC-V), and
forward it to the kernel through a new "linux,uefi-secure-boot" FDT
property. The early init path then calls efi_set_secure_boot(), which
on kernels with CONFIG_LOCK_DOWN_IN_EFI_SECURE_BOOT triggers kernel
lockdown — analogous to how x86 already does it via boot_params.

Based on the Debian patch
"arm64-add-kernel-config-option-to-lock-down-when-in-Secure-Boot-mode.patch"
by Linn Crosetto. The original subject incorrectly implied an arm64-only
change; the patch in fact only touches generic drivers/firmware/efi/ code
that is shared by all FDT-based EFI architectures (ARM, arm64, RISC-V).
Re-titled and re-described accordingly; the code is unchanged.

Original commit message:

  arm64: add kernel config option to lock down when in Secure Boot mode
  Add a kernel configuration option to lock down the kernel, to restrict
  userspace's ability to modify the running kernel when UEFI Secure Boot
  is enabled. Based on the x86 patch by Matthew Garrett.
  Determine the state of Secure Boot in the EFI stub and pass this to the
  kernel using the FDT.

  Signed-off-by: Linn Crosetto <linn@hpe.com>

Signed-off-by: Linn Crosetto <linn@hpe.com>
[egori: re-titled and rewrote commit message; no code changes]
Signed-off-by: Egor Ignatov <egori@altlinux.org>
---
 drivers/firmware/efi/efi-init.c    |  5 ++++-
 drivers/firmware/efi/fdtparams.c   | 12 +++++++++++-
 drivers/firmware/efi/libstub/fdt.c |  6 ++++++
 include/linux/efi.h                |  3 ++-
 4 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/firmware/efi/efi-init.c b/drivers/firmware/efi/efi-init.c
index 6103b1a082..dea8d67c71 100644
--- a/drivers/firmware/efi/efi-init.c
+++ b/drivers/firmware/efi/efi-init.c
@@ -234,9 +234,10 @@ void __init efi_init(void)
 {
 	struct efi_memory_map_data data;
 	u64 efi_system_table;
+	u32 secure_boot;
 
 	/* Grab UEFI information placed in FDT by stub */
-	efi_system_table = efi_get_fdt_params(&data);
+	efi_system_table = efi_get_fdt_params(&data, &secure_boot);
 	if (!efi_system_table)
 		return;
 
@@ -258,6 +259,8 @@ void __init efi_init(void)
 		return;
 	}
 
+	efi_set_secure_boot(secure_boot);
+
 	reserve_regions();
 	/*
 	 * For memblock manipulation, the cap should come after the memblock_add().
diff --git a/drivers/firmware/efi/fdtparams.c b/drivers/firmware/efi/fdtparams.c
index b815d2a754..6f05b73c14 100644
--- a/drivers/firmware/efi/fdtparams.c
+++ b/drivers/firmware/efi/fdtparams.c
@@ -16,6 +16,7 @@ enum {
 	MMSIZE,
 	DCSIZE,
 	DCVERS,
+	SBMODE,
 
 	PARAMCOUNT
 };
@@ -26,6 +27,7 @@ static __initconst const char name[][22] = {
 	[MMSIZE] = "MemMap Size          ",
 	[DCSIZE] = "MemMap Desc. Size    ",
 	[DCVERS] = "MemMap Desc. Version ",
+	[SBMODE] = "Secure Boot Enabled  ",
 };
 
 static __initconst const struct {
@@ -43,6 +45,7 @@ static __initconst const struct {
 			[MMSIZE] = "xen,uefi-mmap-size",
 			[DCSIZE] = "xen,uefi-mmap-desc-size",
 			[DCVERS] = "xen,uefi-mmap-desc-ver",
+			[SBMODE] = "",
 		}
 	}, {
 #endif
@@ -53,6 +56,7 @@ static __initconst const struct {
 			[MMSIZE] = "linux,uefi-mmap-size",
 			[DCSIZE] = "linux,uefi-mmap-desc-size",
 			[DCVERS] = "linux,uefi-mmap-desc-ver",
+			[SBMODE] = "linux,uefi-secure-boot",
 		}
 	}
 };
@@ -64,6 +68,11 @@ static int __init efi_get_fdt_prop(const void *fdt, int node, const char *pname,
 	int len;
 	u64 val;
 
+	if (!pname[0]) {
+		memset(var, 0, size);
+		return 0;
+	}
+
 	prop = fdt_getprop(fdt, node, pname, &len);
 	if (!prop)
 		return 1;
@@ -81,7 +90,7 @@ static int __init efi_get_fdt_prop(const void *fdt, int node, const char *pname,
 	return 0;
 }
 
-u64 __init efi_get_fdt_params(struct efi_memory_map_data *mm)
+u64 __init efi_get_fdt_params(struct efi_memory_map_data *mm, u32 *secure_boot)
 {
 	const void *fdt = initial_boot_params;
 	unsigned long systab;
@@ -95,6 +104,7 @@ u64 __init efi_get_fdt_params(struct efi_memory_map_data *mm)
 		[MMSIZE] = { &mm->size,		sizeof(mm->size) },
 		[DCSIZE] = { &mm->desc_size,	sizeof(mm->desc_size) },
 		[DCVERS] = { &mm->desc_version,	sizeof(mm->desc_version) },
+		[SBMODE] = { secure_boot,		sizeof(*secure_boot) },
 	};
 
 	BUILD_BUG_ON(ARRAY_SIZE(target) != ARRAY_SIZE(name));
diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c
index 23b3543d30..d4fea86bd3 100644
--- a/drivers/firmware/efi/libstub/fdt.c
+++ b/drivers/firmware/efi/libstub/fdt.c
@@ -132,6 +132,12 @@ static efi_status_t update_fdt(void *orig_fdt, unsigned long orig_fdt_size,
 		}
 	}
 
+	fdt_val32 = cpu_to_fdt32(efi_get_secureboot());
+	status = fdt_setprop(fdt, node, "linux,uefi-secure-boot",
+			     &fdt_val32, sizeof(fdt_val32));
+	if (status)
+		goto fdt_set_fail;
+
 	/* Shrink the FDT back to its minimum size: */
 	fdt_pack(fdt);
 
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 7eed6dcb70..9d2d81313a 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -758,7 +758,8 @@ extern int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md);
 extern int __efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md);
 extern void efi_mem_reserve(phys_addr_t addr, u64 size);
 extern int efi_mem_reserve_persistent(phys_addr_t addr, u64 size);
-extern u64 efi_get_fdt_params(struct efi_memory_map_data *data);
+extern u64 efi_get_fdt_params(struct efi_memory_map_data *data,
+			      u32 *secure_boot);
 extern struct kobject *efi_kobj;
 
 extern int efi_reboot_quirk_mode;
-- 
2.50.1