arm64: efi: invoke EFI_RNG_PROTOCOL to supply KASLR randomness
Since arm64 does not use a decompressor that supplies an execution
environment where it is feasible to some extent to provide a source of
randomness, the arm64 KASLR kernel depends on the bootloader to supply
some random bits in the /chosen/kaslr-seed DT property upon kernel entry.
On UEFI systems, we can use the EFI_RNG_PROTOCOL, if supplied, to obtain
some random bits. At the same time, use it to randomize the offset of the
kernel Image in physical memory.
Reviewed-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
index 3397902..4deb3e7 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c
@@ -18,6 +18,8 @@
#include "efistub.h"
+bool __nokaslr;
+
static int efi_secureboot_enabled(efi_system_table_t *sys_table_arg)
{
static efi_guid_t const var_guid = EFI_GLOBAL_VARIABLE_GUID;
@@ -207,14 +209,6 @@
pr_efi_err(sys_table, "Failed to find DRAM base\n");
goto fail;
}
- status = handle_kernel_image(sys_table, image_addr, &image_size,
- &reserve_addr,
- &reserve_size,
- dram_base, image);
- if (status != EFI_SUCCESS) {
- pr_efi_err(sys_table, "Failed to relocate kernel\n");
- goto fail;
- }
/*
* Get the command line from EFI, using the LOADED_IMAGE
@@ -224,7 +218,28 @@
cmdline_ptr = efi_convert_cmdline(sys_table, image, &cmdline_size);
if (!cmdline_ptr) {
pr_efi_err(sys_table, "getting command line via LOADED_IMAGE_PROTOCOL\n");
- goto fail_free_image;
+ goto fail;
+ }
+
+ /* check whether 'nokaslr' was passed on the command line */
+ if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
+ static const u8 default_cmdline[] = CONFIG_CMDLINE;
+ const u8 *str, *cmdline = cmdline_ptr;
+
+ if (IS_ENABLED(CONFIG_CMDLINE_FORCE))
+ cmdline = default_cmdline;
+ str = strstr(cmdline, "nokaslr");
+ if (str == cmdline || (str > cmdline && *(str - 1) == ' '))
+ __nokaslr = true;
+ }
+
+ status = handle_kernel_image(sys_table, image_addr, &image_size,
+ &reserve_addr,
+ &reserve_size,
+ dram_base, image);
+ if (status != EFI_SUCCESS) {
+ pr_efi_err(sys_table, "Failed to relocate kernel\n");
+ goto fail_free_cmdline;
}
status = efi_parse_options(cmdline_ptr);
@@ -244,7 +259,7 @@
if (status != EFI_SUCCESS) {
pr_efi_err(sys_table, "Failed to load device tree!\n");
- goto fail_free_cmdline;
+ goto fail_free_image;
}
}
@@ -286,12 +301,11 @@
efi_free(sys_table, initrd_size, initrd_addr);
efi_free(sys_table, fdt_size, fdt_addr);
-fail_free_cmdline:
- efi_free(sys_table, cmdline_size, (unsigned long)cmdline_ptr);
-
fail_free_image:
efi_free(sys_table, image_size, *image_addr);
efi_free(sys_table, reserve_size, reserve_addr);
+fail_free_cmdline:
+ efi_free(sys_table, cmdline_size, (unsigned long)cmdline_ptr);
fail:
return EFI_ERROR;
}