This patch implements CONFIG_DEBUG_RODATA 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, their might be performance
impact. For this reason, we keep it OFF by default.
Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
---
v2: For ftrace, only change the attributes of the page to be modified
v3: Changing the rights is performed in patch_instruction() instead of
being done only in ftrace, so that other functionnalities like
jump_label also works.
arch/powerpc/Kconfig.debug | 11 +++++++++
arch/powerpc/include/asm/pgtable.h | 8 +++++++
arch/powerpc/lib/code-patching.c | 9 ++++++++
arch/powerpc/mm/init_32.c | 3 ++-
arch/powerpc/mm/pgtable_32.c | 46 ++++++++++++++++++++++++++++++++++++++
5 files changed, 76 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index c86df246339e..047f91564e52 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -369,4 +369,15 @@ config PPC_HTDUMP
def_bool y
depends on PPC_PTDUMP && PPC_BOOK3S
+config DEBUG_RODATA
+ bool "Write protect kernel read-only data structures"
+ depends on DEBUG_KERNEL && PPC32
+ default n
+ help
+ Mark the kernel read-only data as write-protected in the pagetables,
+ in order to catch accidental (and incorrect) writes to such const
+ data. This option may have a performance impact because block
+ mapping via BATs etc... will be disabled.
+ If in doubt, say "N".
+
endmenu
diff --git a/arch/powerpc/include/asm/pgtable.h
b/arch/powerpc/include/asm/pgtable.h
index dd01212935ac..142337f3b745 100644
--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h
@@ -80,6 +80,14 @@ unsigned long vmalloc_to_phys(void *vmalloc_addr);
void pgtable_cache_add(unsigned shift, void (*ctor)(void *));
void pgtable_cache_init(void);
+
+#ifdef CONFIG_DEBUG_RODATA
+void set_kernel_text_rw(unsigned long addr);
+void set_kernel_text_ro(unsigned long addr);
+#else
+static inline void set_kernel_text_rw(unsigned long addr) {}
+static inline void set_kernel_text_ro(unsigned long addr) {}
+#endif
#endif /* __ASSEMBLY__ */
#endif /* _ASM_POWERPC_PGTABLE_H */
diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 500b0f6a0b64..8c7ae100bcc2 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -17,12 +17,21 @@
#include <linux/uaccess.h>
#include <linux/kprobes.h>
+static DEFINE_SPINLOCK(patch_lock);
int patch_instruction(unsigned int *addr, unsigned int instr)
{
int err;
+ unsigned long flags;
+ spin_lock_irqsave(&patch_lock, flags);
+
+ set_kernel_text_rw((unsigned long)addr);
__put_user_size(instr, addr, 4, err);
+ set_kernel_text_ro((unsigned long)addr);
+
+ spin_unlock_irqrestore(&patch_lock, flags);
+
if (err)
return err;
asm ("dcbst 0, %0; sync; icbi 0,%0; sync; isync" : : "r" (addr));
diff --git a/arch/powerpc/mm/init_32.c b/arch/powerpc/mm/init_32.c
index 8a7c38b8d335..e39c812b97ca 100644
--- a/arch/powerpc/mm/init_32.c
+++ b/arch/powerpc/mm/init_32.c
@@ -109,7 +109,8 @@ void __init MMU_setup(void)
if (strstr(boot_command_line, "noltlbs")) {
__map_without_ltlbs = 1;
}
- if (debug_pagealloc_enabled()) {
+ if (debug_pagealloc_enabled() ||
+ IS_ENABLED(CONFIG_DEBUG_RODATA)) {
__map_without_bats = 1;
__map_without_ltlbs = 1;
}
diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
index 31728f3cdd20..5f78fd9ad492 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 +376,51 @@ void remap_init_ram(void)
change_page_attr(page, numpages, PAGE_KERNEL);
}
+#ifdef CONFIG_DEBUG_RODATA
+static bool kernel_set_to_readonly __read_mostly;
+
+void set_kernel_text_rw(unsigned long addr)
+{
+ if (!kernel_set_to_readonly)
+ return;
+
+ if (core_kernel_text(addr))
+ change_page_attr(virt_to_page(addr), 1, PAGE_KERNEL_X);
+}
+
+void set_kernel_text_ro(unsigned long addr)
+{
+ if (!kernel_set_to_readonly)
+ return;
+
+ if (core_kernel_text(addr))
+ change_page_attr(virt_to_page(addr), 1, PAGE_KERNEL_ROX);
+}
+
+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);
+
+ kernel_set_to_readonly = true;
+}
+#endif
+
#ifdef CONFIG_DEBUG_PAGEALLOC
void __kernel_map_pages(struct page *page, int numpages, int enable)
{
--
2.12.0
