linux-kernel - [PATCH 3/5] RISC-V: Enforce protections for kernel sections early

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Date:   Fri,  9 Oct 2020 14:13:42 -0700
From:   Atish Patra <atish.patra@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Atish Patra <atish.patra@....com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anup Patel <anup@...infault.org>,
        Ard Biesheuvel <ardb@...nel.org>, Borislav Petkov <bp@...e.de>,
        Greentime Hu <greentime.hu@...ive.com>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Kees Cook <keescook@...omium.org>,
        linux-riscv@...ts.infradead.org,
        Michel Lespinasse <walken@...gle.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Zong Li <zong.li@...ive.com>
Subject: [PATCH 3/5] RISC-V: Enforce protections for kernel sections early

Currently, all memblocks are mapped with PAGE_KERNEL_EXEC and the strict
permissions are only enforced after /init starts. This leaves the kernel
vulnerable from possible buggy built-in modules.

Apply permissions to individual sections as early as possible.

Signed-off-by: Atish Patra <atish.patra@....com>
---
 arch/riscv/include/asm/set_memory.h |  2 ++
 arch/riscv/kernel/setup.c           |  2 ++
 arch/riscv/mm/init.c                | 11 +++++++++--
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
index 4c5bae7ca01c..4cc3a4e2afd3 100644
--- a/arch/riscv/include/asm/set_memory.h
+++ b/arch/riscv/include/asm/set_memory.h
@@ -15,11 +15,13 @@ int set_memory_ro(unsigned long addr, int numpages);
 int set_memory_rw(unsigned long addr, int numpages);
 int set_memory_x(unsigned long addr, int numpages);
 int set_memory_nx(unsigned long addr, int numpages);
+void protect_kernel_text_data(void);
 #else
 static inline int set_memory_ro(unsigned long addr, int numpages) { return 0; }
 static inline int set_memory_rw(unsigned long addr, int numpages) { return 0; }
 static inline int set_memory_x(unsigned long addr, int numpages) { return 0; }
 static inline int set_memory_nx(unsigned long addr, int numpages) { return 0; }
+static inline void protect_kernel_text_data(void) {};
 #endif
 
 int set_direct_map_invalid_noflush(struct page *page);
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index a5cac440aadf..4176a2affd1d 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -23,6 +23,7 @@
 #include <asm/cpu_ops.h>
 #include <asm/early_ioremap.h>
 #include <asm/setup.h>
+#include <asm/set_memory.h>
 #include <asm/sections.h>
 #include <asm/sbi.h>
 #include <asm/tlbflush.h>
@@ -93,6 +94,7 @@ void __init setup_arch(char **cmdline_p)
 #if IS_ENABLED(CONFIG_RISCV_SBI)
 	sbi_init();
 #endif
+	protect_kernel_text_data();
 #ifdef CONFIG_SWIOTLB
 	swiotlb_init(1);
 #endif
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index c888c4470b34..7859a1d1b34d 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -623,7 +623,7 @@ static inline void setup_vm_final(void)
 #endif /* CONFIG_MMU */
 
 #ifdef CONFIG_STRICT_KERNEL_RWX
-void mark_rodata_ro(void)
+void protect_kernel_text_data(void)
 {
 	unsigned long text_start = (unsigned long)_text;
 	unsigned long text_end = (unsigned long)_etext;
@@ -632,9 +632,16 @@ void mark_rodata_ro(void)
 	unsigned long max_low = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
 
 	set_memory_ro(text_start, (text_end - text_start) >> PAGE_SHIFT);
-	set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
 	set_memory_nx(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
 	set_memory_nx(data_start, (max_low - data_start) >> PAGE_SHIFT);
+}
+
+void mark_rodata_ro(void)
+{
+	unsigned long rodata_start = (unsigned long)__start_rodata;
+	unsigned long data_start = (unsigned long)_data;
+
+	set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
 
 	debug_checkwx();
 }
-- 
2.25.1