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 <[email protected]>
[bwh: Forward-ported to 4.10: adjust context]
[Lukas Wunner: Forward-ported to 4.11: drop parts applied upstream]
[bwh: Forward-ported to 4.15 and lockdown patch set:
 - Pass result of efi_get_secureboot() in stub through to
   efi_set_secure_boot() in main kernel
 - Use lockdown API and naming]
[bwh: Forward-ported to 4.19.3: adjust context in update_fdt()]
[dannf: Moved init_lockdown() call after uefi_init(), fixing SB detection]
[bwh: Drop call to init_lockdown(), as efi_set_secure_boot() now calls this]
[bwh: Forward-ported to 5.6: efi_get_secureboot() no longer takes a
 sys_table parameter]
[bwh: Forward-ported to 5.7: EFI initialisation from FDT was rewritten, so:
 - Add Secure Boot mode to the parameter enumeration in fdtparams.c
 - Add a parameter to efi_get_fdt_params() to return the Secure Boot mode
 - Since Xen does not have a property name defined for Secure Boot mode,
   change efi_get_fdt_prop() to handle a missing property name by clearing
   the output variable]
[Salvatore Bonaccorso: Forward-ported to 5.10: f30f242 ("efi: Rename
arm-init to efi-init common for all arch") renamed arm-init.c to efi-init.c]

Orabug: 34304810
Signed-off-by: Eric Snowberg <[email protected]>
Reviewed-by: Konrad Rzeszutek Wilk <[email protected]>

Author: Linn Crosetto

drivers/firmware/efi/efi-init.c

@@ -213,9 +213,10 @@ 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;
 
@@ -237,6 +238,8 @@ 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().

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));

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);
 

include/linux/efi.h

@@ -764,7 +764,7 @@ 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;