If unsure, say N.
+config RANDOMIZE_BASE
+ bool "Randomize the address of the kernel image"
+ select RELOCATABLE
+ depends on MMU && 64BIT && !XIP_KERNEL
+ help
+ Randomizes the virtual address at which the kernel image is
+ loaded, as a security feature that deters exploit attempts
+ relying on knowledge of the location of kernel internals.
+
+ 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.
+
endmenu # "Kernel features"
menu "Boot options"
struct kernel_mapping {
unsigned long page_offset;
unsigned long virt_addr;
+ unsigned long virt_offset;
uintptr_t phys_addr;
uintptr_t size;
/* Offset between linear mapping virtual address and kernel load address */
#define sym_to_pfn(x) __phys_to_pfn(__pa_symbol(x))
+unsigned long kaslr_offset(void);
+
#endif /* __ASSEMBLY__ */
#define virt_addr_valid(vaddr) ({ \
$(obj)/ctype.o: $(srctree)/lib/ctype.c FORCE
$(call if_changed_rule,cc_o_c)
-obj-y := cmdline_early.pi.o string.pi.o ctype.pi.o lib-fdt.pi.o lib-fdt_ro.pi.o
+obj-y := cmdline_early.pi.o fdt_early.pi.o string.pi.o ctype.pi.o lib-fdt.pi.o lib-fdt_ro.pi.o
extra-y := $(patsubst %.pi.o,%.o,$(obj-y))
* LLVM complain because the function is actually unused in this file).
*/
u64 set_satp_mode_from_cmdline(uintptr_t dtb_pa);
+bool set_nokaslr_from_cmdline(uintptr_t dtb_pa);
static char *get_early_cmdline(uintptr_t dtb_pa)
{
return match_noXlvl(cmdline);
}
+
+static bool match_nokaslr(char *cmdline)
+{
+ return strstr(cmdline, "nokaslr");
+}
+
+bool set_nokaslr_from_cmdline(uintptr_t dtb_pa)
+{
+ char *cmdline = get_early_cmdline(dtb_pa);
+
+ return match_nokaslr(cmdline);
+}
--- /dev/null
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/types.h>
+#include <linux/init.h>
+#include <linux/libfdt.h>
+
+/*
+ * Declare the functions that are exported (but prefixed) here so that LLVM
+ * does not complain it lacks the 'static' keyword (which, if added, makes
+ * LLVM complain because the function is actually unused in this file).
+ */
+u64 get_kaslr_seed(uintptr_t dtb_pa);
+
+u64 get_kaslr_seed(uintptr_t dtb_pa)
+{
+ int node, len;
+ fdt64_t *prop;
+ u64 ret;
+
+ node = fdt_path_offset((void *)dtb_pa, "/chosen");
+ if (node < 0)
+ return 0;
+
+ prop = fdt_getprop_w((void *)dtb_pa, node, "kaslr-seed", &len);
+ if (!prop || len != sizeof(u64))
+ return 0;
+
+ ret = fdt64_to_cpu(*prop);
+ *prop = 0;
+ return ret;
+}
#endif
}
+#ifdef CONFIG_RANDOMIZE_BASE
+extern bool __init __pi_set_nokaslr_from_cmdline(uintptr_t dtb_pa);
+extern u64 __init __pi_get_kaslr_seed(uintptr_t dtb_pa);
+
+static int __init print_nokaslr(char *p)
+{
+ pr_info("Disabled KASLR");
+ return 0;
+}
+early_param("nokaslr", print_nokaslr);
+
+unsigned long kaslr_offset(void)
+{
+ return kernel_map.virt_offset;
+}
+#endif
+
asmlinkage void __init setup_vm(uintptr_t dtb_pa)
{
pmd_t __maybe_unused fix_bmap_spmd, fix_bmap_epmd;
- kernel_map.virt_addr = KERNEL_LINK_ADDR;
+#ifdef CONFIG_RANDOMIZE_BASE
+ if (!__pi_set_nokaslr_from_cmdline(dtb_pa)) {
+ u64 kaslr_seed = __pi_get_kaslr_seed(dtb_pa);
+ u32 kernel_size = (uintptr_t)(&_end) - (uintptr_t)(&_start);
+ u32 nr_pos;
+
+ /*
+ * Compute the number of positions available: we are limited
+ * by the early page table that only has one PUD and we must
+ * be aligned on PMD_SIZE.
+ */
+ nr_pos = (PUD_SIZE - kernel_size) / PMD_SIZE;
+
+ kernel_map.virt_offset = (kaslr_seed % nr_pos) * PMD_SIZE;
+ }
+#endif
+
+ kernel_map.virt_addr = KERNEL_LINK_ADDR + kernel_map.virt_offset;
kernel_map.page_offset = _AC(CONFIG_PAGE_OFFSET, UL);
#ifdef CONFIG_XIP_KERNEL