[PATCH v7 26/33] arm64: head: move memstart_offset_seed handling to C code

[Ard Biesheuvel]

Now that we can set BSS variables from the early code running from the
ID map, we can set memstart_offset_seed directly from the C code that
derives the value instead of passing it back and forth between C and asm
code.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 arch/arm64/kernel/head.S           | 7 -------
 arch/arm64/kernel/image-vars.h     | 2 ++
 arch/arm64/kernel/kaslr.c          | 2 +-
 arch/arm64/kernel/pi/kaslr_early.c | 6 +++++-
 4 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 5f1476c0f3a33d75..4b88ca8766133fd3 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -81,7 +81,6 @@
 	 *  x21        primary_entry() .. start_kernel()        FDT pointer passed at boot in x0
 	 *  x22        create_idmap() .. start_kernel()         ID map VA of the DT blob
 	 *  x23        __primary_switch()                       physical misalignment/KASLR offset
-	 *  x24        __primary_switch()                       linear map KASLR seed
 	 *  x25        primary_entry() .. start_kernel()        supported VA size
 	 *  x28        create_idmap()                           callee preserved temp register
 	 */
@@ -431,11 +430,6 @@ SYM_FUNC_START_LOCAL(__primary_switched)
 	str	x25, [x8]			// ... observes the correct value
 	dc	civac, x8			// Make visible to booting secondaries
 #endif
-
-#ifdef CONFIG_RANDOMIZE_BASE
-	adrp	x5, memstart_offset_seed	// Save KASLR linear map seed
-	strh	w24, [x5, :lo12:memstart_offset_seed]
-#endif
 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
 	bl	kasan_early_init
 #endif
@@ -705,7 +699,6 @@ SYM_FUNC_START_LOCAL(__primary_switch)
 #ifdef CONFIG_RANDOMIZE_BASE
 	mov	x0, x22
 	bl	__pi_kaslr_early_init
-	and	x24, x0, #SZ_2M - 1		// capture memstart offset seed
 	bic	x0, x0, #SZ_2M - 1
 	orr	x23, x23, x0			// record kernel offset
 #endif
diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index 6ff6efbc1ce98ba6..6c6dd100a9cbadf8 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -41,6 +41,8 @@ PROVIDE(__pi___memcpy			= __pi_memcpy);
 PROVIDE(__pi___memmove			= __pi_memmove);
 PROVIDE(__pi___memset			= __pi_memset);
 
+PROVIDE(__pi_memstart_offset_seed	= memstart_offset_seed);
+
 PROVIDE(__pi_id_aa64isar1_override	= id_aa64isar1_override);
 PROVIDE(__pi_id_aa64isar2_override	= id_aa64isar2_override);
 PROVIDE(__pi_id_aa64mmfr1_override	= id_aa64mmfr1_override);
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index 5d4ce7f5f157bb3f..37a9deed2aec9297 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -21,7 +21,7 @@
 #include <asm/setup.h>
 
 u64 __ro_after_init module_alloc_base;
-u16 __initdata memstart_offset_seed;
+u16 memstart_offset_seed;
 
 static int __init kaslr_init(void)
 {
diff --git a/arch/arm64/kernel/pi/kaslr_early.c b/arch/arm64/kernel/pi/kaslr_early.c
index 934e95fbd4278d0b..c46bccd593f2ff6b 100644
--- a/arch/arm64/kernel/pi/kaslr_early.c
+++ b/arch/arm64/kernel/pi/kaslr_early.c
@@ -15,6 +15,8 @@
 #include <asm/archrandom.h>
 #include <asm/memory.h>
 
+extern u16 memstart_offset_seed;
+
 static u64 __init get_kaslr_seed(void *fdt)
 {
 	static char const chosen_str[] __initconst = "chosen";
@@ -51,6 +53,8 @@ asmlinkage u64 __init kaslr_early_init(void *fdt)
 			return 0;
 	}
 
+	memstart_offset_seed = seed & U16_MAX;
+
 	/*
 	 * OK, so we are proceeding with KASLR enabled. Calculate a suitable
 	 * kernel image offset from the seed. Let's place the kernel in the
@@ -58,5 +62,5 @@ asmlinkage u64 __init kaslr_early_init(void *fdt)
 	 * the lower and upper quarters to avoid colliding with other
 	 * allocations.
 	 */
-	return BIT(VA_BITS_MIN - 3) + (seed & GENMASK(VA_BITS_MIN - 3, 0));
+	return BIT(VA_BITS_MIN - 3) + (seed & GENMASK(VA_BITS_MIN - 3, 16));
 }
-- 
2.35.1