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Subject[PATCH v2 3/5] powerpc/mm: Implement STRICT_KERNEL_RWX on PPC32
Date
This patch implements STRICT_KERNEL_RWX on PPC32.

As for CONFIG_DEBUG_PAGEALLOC, it deactivates BAT and LTLB mappings
in order to allow page protection setup at the level of each page.

As BAT/LTLB mappings are deactivated, there might be a performance
impact.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/Kconfig | 2 +-
arch/powerpc/kernel/vmlinux.lds.S | 2 +-
arch/powerpc/mm/init_32.c | 6 ++++++
arch/powerpc/mm/pgtable_32.c | 24 ++++++++++++++++++++++++
4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 36f858c37ca7..07c51f31f8a6 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -165,7 +165,7 @@ config PPC
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_TRACEHOOK
- select ARCH_HAS_STRICT_KERNEL_RWX if (PPC_BOOK3S_64 && !RELOCATABLE && !HIBERNATION)
+ select ARCH_HAS_STRICT_KERNEL_RWX if ((PPC_BOOK3S_64 || PPC32) && !RELOCATABLE && !HIBERNATION)
select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
select HAVE_CBPF_JIT if !PPC64
select HAVE_CONTEXT_TRACKING if PPC64
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index b1a250560198..882628fa6987 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -8,7 +8,7 @@
#include <asm/cache.h>
#include <asm/thread_info.h>

-#ifdef CONFIG_STRICT_KERNEL_RWX
+#if defined(CONFIG_STRICT_KERNEL_RWX) && !defined(CONFIG_PPC32)
#define STRICT_ALIGN_SIZE (1 << 24)
#else
#define STRICT_ALIGN_SIZE PAGE_SIZE
diff --git a/arch/powerpc/mm/init_32.c b/arch/powerpc/mm/init_32.c
index 8a7c38b8d335..7d5fee1bb116 100644
--- a/arch/powerpc/mm/init_32.c
+++ b/arch/powerpc/mm/init_32.c
@@ -113,6 +113,12 @@ void __init MMU_setup(void)
__map_without_bats = 1;
__map_without_ltlbs = 1;
}
+#ifdef CONFIG_STRICT_KERNEL_RWX
+ if (rodata_enabled) {
+ __map_without_bats = 1;
+ __map_without_ltlbs = 1;
+ }
+#endif
}

/*
diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
index a87a0b12b032..0b70ccd53de8 100644
--- a/arch/powerpc/mm/pgtable_32.c
+++ b/arch/powerpc/mm/pgtable_32.c
@@ -34,6 +34,7 @@
#include <asm/fixmap.h>
#include <asm/io.h>
#include <asm/setup.h>
+#include <asm/sections.h>

#include "mmu_decl.h"

@@ -375,6 +376,29 @@ void remap_init_ram(void)
change_page_attr(page, numpages, PAGE_KERNEL);
}

+#ifdef CONFIG_STRICT_KERNEL_RWX
+void mark_rodata_ro(void)
+{
+ struct page *page;
+ unsigned long numpages;
+
+ page = virt_to_page(_stext);
+ numpages = PFN_UP((unsigned long)_etext) -
+ PFN_DOWN((unsigned long)_stext);
+
+ change_page_attr(page, numpages, PAGE_KERNEL_ROX);
+ /*
+ * mark .rodata as read only. Use __init_begin rather than __end_rodata
+ * to cover NOTES and EXCEPTION_TABLE.
+ */
+ page = virt_to_page(__start_rodata);
+ numpages = PFN_UP((unsigned long)__init_begin) -
+ PFN_DOWN((unsigned long)__start_rodata);
+
+ change_page_attr(page, numpages, PAGE_KERNEL_RO);
+}
+#endif
+
#ifdef CONFIG_DEBUG_PAGEALLOC
void __kernel_map_pages(struct page *page, int numpages, int enable)
{
--
2.12.0
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