linux-kernel - [PATCH RFC 6/8] riscv/kaslr: clear the original kernel image

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Message-Id: <8373a9d18958b99b72ed9499786dffe45adf9617.1584352425.git.zong.li@sifive.com>
Date:   Tue, 24 Mar 2020 15:30:51 +0800
From:   Zong Li <zong.li@...ive.com>
To:     palmer@...belt.com, paul.walmsley@...ive.com, alex@...ti.fr,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Zong Li <zong.li@...ive.com>
Subject: [PATCH RFC 6/8] riscv/kaslr: clear the original kernel image

After completing final page table, we can clear original kernel image
and remove executable permission.

Signed-off-by: Zong Li <zong.li@...ive.com>
---
 arch/riscv/include/asm/kaslr.h | 12 ++++++++++++
 arch/riscv/kernel/kaslr.c      | 12 ++++++++++++
 arch/riscv/mm/init.c           |  6 ++++++
 3 files changed, 30 insertions(+)
 create mode 100644 arch/riscv/include/asm/kaslr.h

diff --git a/arch/riscv/include/asm/kaslr.h b/arch/riscv/include/asm/kaslr.h
new file mode 100644
index 000000000000..b165fe71dd4a
--- /dev/null
+++ b/arch/riscv/include/asm/kaslr.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 SiFive
+ * Copyright (C) 2020 Zong Li <zong.li@...ive.com>
+ */
+
+#ifndef _ASM_RISCV_KASLR_H
+#define _ASM_RISCV_KASLR_H
+
+void __init kaslr_late_init(void);
+
+#endif /* _ASM_RISCV_KASLR_H */
diff --git a/arch/riscv/kernel/kaslr.c b/arch/riscv/kernel/kaslr.c
index 59001d6fdfc3..0bd30831c455 100644
--- a/arch/riscv/kernel/kaslr.c
+++ b/arch/riscv/kernel/kaslr.c
@@ -356,6 +356,18 @@ static __init uintptr_t get_random_offset(u64 seed, uintptr_t kernel_size)
 	return get_legal_offset(random, kernel_size_align);
 }
 
+void __init kaslr_late_init(void)
+{
+	uintptr_t kernel_size;
+
+	/* Clear original kernel image. */
+	if (kaslr_offset) {
+		kernel_size = (uintptr_t) _end - (uintptr_t) _start;
+		memset((void *)PAGE_OFFSET, 0, kernel_size);
+		set_memory_nx(PAGE_OFFSET, kaslr_offset >> PAGE_SHIFT);
+	}
+}
+
 uintptr_t __init kaslr_early_init(void)
 {
 	u64 seed;
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 34c6ecf2c599..08e2ce170533 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -15,6 +15,7 @@
 #include <linux/set_memory.h>
 #ifdef CONFIG_RELOCATABLE
 #include <linux/elf.h>
+#include <asm/kaslr.h>
 #endif
 
 #include <asm/fixmap.h>
@@ -649,6 +650,11 @@ static void __init setup_vm_final(void)
 	/* Move to swapper page table */
 	csr_write(CSR_SATP, PFN_DOWN(__pa_symbol(swapper_pg_dir)) | SATP_MODE);
 	local_flush_tlb_all();
+
+#ifdef CONFIG_RANDOMIZE_BASE
+	/* Clear orignial kernel image and set the right permission. */
+	kaslr_late_init();
+#endif
 }
 
 void free_initmem(void)
-- 
2.25.1