[PATCH v5 2/3] LoongArch: Skip relocation-time KASLR if already applied

[WANG Rui]

When the kernel is relocated during early boot (efistub or kexec_file),
a randomized load address may has already been selected and applied. In
this case, performing KASLR again in relocate.c is unnecessary.

Note: strictly-defined KASLR means the kernel's final runtime address
has a random offset from the kernel's load address, which is implemented
in relocate.c; broadly-defined KALSR means the kernel's final runtime
address has a random offset from the kernel's link address (a.k.a.
VMLINUX_LOAD_ADDRESS), which also include the efistlub implementation,
kexec_file implementation and QEMU direct kernel boot. kaslr_disabled()
return true only means strictly-defined KASLR is disabled.

Acked-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Co-authored-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
Signed-off-by: WANG Rui <r@xxxxxx>
Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
---
 arch/loongarch/kernel/relocate.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/loongarch/kernel/relocate.c b/arch/loongarch/kernel/relocate.c
index 16f6a9b39659..0a045964fad5 100644
--- a/arch/loongarch/kernel/relocate.c
+++ b/arch/loongarch/kernel/relocate.c
@@ -134,11 +134,23 @@ early_param("nokaslr", nokaslr);
 
 #define KASLR_DISABLED_MESSAGE "KASLR is disabled by %s in %s cmdline.\n"
 
+/*
+ * Note: strictly-defined KASLR means the kernel's final runtime address
+ * has a random offset from the kernel's load address, which is implemented
+ * in relocate.c; broadly-defined KALSR means the kernel's final runtime
+ * address has a random offset from the kernel's link address (a.k.a.
+ * VMLINUX_LOAD_ADDRESS), which also include the efistlub implementation,
+ * kexec_file implementation and QEMU direct kernel boot. kaslr_disabled()
+ * return true only means strictly-defined KASLR is disabled.
+ */
 static inline __init bool kaslr_disabled(void)
 {
 	char *str;
 	const char *builtin_cmdline = CONFIG_CMDLINE;
 
+	if (kaslr_offset())
+		return true; /* KASLR is performed during early boot. */
+
 	str = strstr(builtin_cmdline, "nokaslr");
 	if (str == builtin_cmdline || (str > builtin_cmdline && *(str - 1) == ' ')) {
 		pr_info(KASLR_DISABLED_MESSAGE, "\'nokaslr\'", "built-in");
-- 
2.54.0