linux-kernel - [PATCH v3 33/60] arm64: head: move memstart_offset

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Message-Id: <20230307140522.2311461-34-ardb@kernel.org>
Date:   Tue,  7 Mar 2023 15:04:55 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux-arm-kernel@...ts.infradead.org,
        Ard Biesheuvel <ardb@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ryan Roberts <ryan.roberts@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Kees Cook <keescook@...omium.org>
Subject: [PATCH v3 33/60] arm64: head: move memstart_offset_seed handling to C code

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@...nel.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