[PATCH v3 33/60] arm64: head: move memstart_offset_seed handling to C code

Ard Biesheuvel
2023-03-07T14:10:25Z

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@kernel.org>
---
arch/arm64/kernel/head.S | 7 -------
arch/arm64/kernel/image-vars.h | 1 +
arch/arm64/kernel/pi/kaslr_early.c | 4 ++++
3 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 70ad180eed364906..81c2dd06420992ea 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -82,7 +82,6 @@
* 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
*/
@@ -483,11 +482,6 @@ 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
@@ -777,7 +771,6 @@ 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 5aa914ea919a1149..b7fa7fbf8fa543a6 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -44,6 +44,7 @@ PROVIDE(__pi_id_aa64smfr0_override = id_aa64smfr0_override);
PROVIDE(__pi_id_aa64zfr0_override = id_aa64zfr0_override);
PROVIDE(__pi_arm64_sw_feature_override = arm64_sw_feature_override);
PROVIDE(__pi__ctype = _ctype);
+PROVIDE(__pi_memstart_offset_seed = memstart_offset_seed);

#ifdef CONFIG_KVM

diff --git a/arch/arm64/kernel/pi/kaslr_early.c b/arch/arm64/kernel/pi/kaslr_early.c
index f2305e276ec36803..eeecee7ffd6fa125 100644
--- a/arch/arm64/kernel/pi/kaslr_early.c
+++ b/arch/arm64/kernel/pi/kaslr_early.c
@@ -16,6 +16,8 @@
#include <asm/memory.h>
#include <asm/pgtable.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
--
2.39.2