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.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
---
arch/arm64/Kconfig | 5 ++
drivers/firmware/efi/libstub/arm-stub.c | 40 ++++++----
drivers/firmware/efi/libstub/arm64-stub.c | 78 ++++++++++++++------
drivers/firmware/efi/libstub/fdt.c | 14 ++++
4 files changed, 102 insertions(+), 35 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 666aacc4c763..630b078a0f73 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -785,6 +785,11 @@ config RANDOMIZE_BASE
It is the bootloader's job to provide entropy, by passing a
random u64 value in /chosen/kaslr-seed at kernel entry.
+ When booting via the UEFI stub, it will invoke the firmware's
+ EFI_RNG_PROTOCOL implementation (if available) to supply entropy
+ to the kernel proper. In addition, it will randomise the physical
+ location of the kernel Image as well.
+
If unsure, say N.
config RANDOMIZE_MODULE_REGION_FULL
diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
index 3397902e4040..4deb3e7faa0e 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 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
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 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
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 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
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 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
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;
}
diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c
index 78dfbd34b6bf..e0e6b74fef8f 100644
--- a/drivers/firmware/efi/libstub/arm64-stub.c
+++ b/drivers/firmware/efi/libstub/arm64-stub.c
@@ -13,6 +13,10 @@
#include <asm/efi.h>
#include <asm/sections.h>
+#include "efistub.h"
+
+extern bool __nokaslr;
+
efi_status_t __init handle_kernel_image(efi_system_table_t *sys_table_arg,
unsigned long *image_addr,
unsigned long *image_size,
@@ -23,26 +27,52 @@ efi_status_t __init handle_kernel_image(efi_system_table_t *sys_table_arg,
{
efi_status_t status;
unsigned long kernel_size, kernel_memsize = 0;
- unsigned long nr_pages;
void *old_image_addr = (void *)*image_addr;
unsigned long preferred_offset;
+ u64 phys_seed = 0;
+
+ if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
+ if (!__nokaslr) {
+ status = efi_get_random_bytes(sys_table_arg,
+ sizeof(phys_seed),
+ (u8 *)&phys_seed);
+ if (status == EFI_NOT_FOUND) {
+ pr_efi(sys_table_arg, "EFI_RNG_PROTOCOL unavailable, no randomness supplied\n");
+ } else if (status != EFI_SUCCESS) {
+ pr_efi_err(sys_table_arg, "efi_get_random_bytes() failed\n");
+ return status;
+ }
+ } else {
+ pr_efi(sys_table_arg, "KASLR disabled on kernel command line\n");
+ }
+ }
/*
* The preferred offset of the kernel Image is TEXT_OFFSET bytes beyond
* a 2 MB aligned base, which itself may be lower than dram_base, as
* long as the resulting offset equals or exceeds it.
*/
- preferred_offset = round_down(dram_base, SZ_2M) + TEXT_OFFSET;
+ preferred_offset = round_down(dram_base, MIN_KIMG_ALIGN) + TEXT_OFFSET;
if (preferred_offset < dram_base)
- preferred_offset += SZ_2M;
+ preferred_offset += MIN_KIMG_ALIGN;
- /* Relocate the image, if required. */
kernel_size = _edata - _text;
- if (*image_addr != preferred_offset) {
- kernel_memsize = kernel_size + (_end - _edata);
+ kernel_memsize = kernel_size + (_end - _edata);
+
+ if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && phys_seed != 0) {
+ /*
+ * If KASLR is enabled, and we have some randomness available,
+ * locate the kernel at a randomized offset in physical memory.
+ */
+ *reserve_size = kernel_memsize + TEXT_OFFSET;
+ status = efi_random_alloc(sys_table_arg, *reserve_size,
+ MIN_KIMG_ALIGN, reserve_addr,
+ phys_seed);
+ *image_addr = *reserve_addr + TEXT_OFFSET;
+ } else {
/*
- * First, try a straight allocation at the preferred offset.
+ * Else, try a straight allocation at the preferred offset.
* This will work around the issue where, if dram_base == 0x0,
* efi_low_alloc() refuses to allocate at 0x0 (to prevent the
* address of the allocation to be mistaken for a FAIL return
@@ -52,27 +82,31 @@ efi_status_t __init handle_kernel_image(efi_system_table_t *sys_table_arg,
* Mustang), we can still place the kernel at the address
* 'dram_base + TEXT_OFFSET'.
*/
+ if (*image_addr == preferred_offset)
+ return EFI_SUCCESS;
+
*image_addr = *reserve_addr = preferred_offset;
- nr_pages = round_up(kernel_memsize, EFI_ALLOC_ALIGN) /
- EFI_PAGE_SIZE;
+ *reserve_size = round_up(kernel_memsize, EFI_ALLOC_ALIGN);
+
status = efi_call_early(allocate_pages, EFI_ALLOCATE_ADDRESS,
- EFI_LOADER_DATA, nr_pages,
+ EFI_LOADER_DATA,
+ *reserve_size / EFI_PAGE_SIZE,
(efi_physical_addr_t *)reserve_addr);
- if (status != EFI_SUCCESS) {
- kernel_memsize += TEXT_OFFSET;
- status = efi_low_alloc(sys_table_arg, kernel_memsize,
- SZ_2M, reserve_addr);
+ }
- if (status != EFI_SUCCESS) {
- pr_efi_err(sys_table_arg, "Failed to relocate kernel\n");
- return status;
- }
- *image_addr = *reserve_addr + TEXT_OFFSET;
+ if (status != EFI_SUCCESS) {
+ *reserve_size = kernel_memsize + TEXT_OFFSET;
+ status = efi_low_alloc(sys_table_arg, *reserve_size,
+ MIN_KIMG_ALIGN, reserve_addr);
+
+ if (status != EFI_SUCCESS) {
+ pr_efi_err(sys_table_arg, "Failed to relocate kernel\n");
+ *reserve_size = 0;
+ return status;
}
- memcpy((void *)*image_addr, old_image_addr, kernel_size);
- *reserve_size = kernel_memsize;
+ *image_addr = *reserve_addr + TEXT_OFFSET;
}
-
+ memcpy((void *)*image_addr, old_image_addr, kernel_size);
return EFI_SUCCESS;
}
diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c
index cf7b7d46302a..6dba78aef337 100644
--- a/drivers/firmware/efi/libstub/fdt.c
+++ b/drivers/firmware/efi/libstub/fdt.c
@@ -147,6 +147,20 @@ efi_status_t update_fdt(efi_system_table_t *sys_table, void *orig_fdt,
if (status)
goto fdt_set_fail;
+ if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
+ efi_status_t efi_status;
+
+ efi_status = efi_get_random_bytes(sys_table, sizeof(fdt_val64),
+ (u8 *)&fdt_val64);
+ if (efi_status == EFI_SUCCESS) {
+ status = fdt_setprop(fdt, node, "kaslr-seed",
+ &fdt_val64, sizeof(fdt_val64));
+ if (status)
+ goto fdt_set_fail;
+ } else if (efi_status != EFI_NOT_FOUND) {
+ return efi_status;
+ }
+ }
return EFI_SUCCESS;
fdt_set_fail:
--
2.5.0
--
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