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>
---
arch/powerpc/Kconfig.debug | 11 +++++++++++
arch/powerpc/include/asm/pgtable.h | 8 ++++++++
arch/powerpc/kernel/ftrace.c | 2 ++
arch/powerpc/mm/init_32.c | 3 ++-
arch/powerpc/mm/pgtable_32.c | 36 ++++++++++++++++++++++++++++++++++++
5 files changed, 59 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..5de74b60ed00 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(void);
+void set_kernel_text_ro(void);
+#else
+static inline void set_kernel_text_rw(void) {}
+static inline void set_kernel_text_ro(void) {}
+#endif
#endif /* __ASSEMBLY__ */
#endif /* _ASM_POWERPC_PGTABLE_H */
diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 32509de6ce4c..4af81fb23653 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -526,7 +526,9 @@ void ftrace_replace_code(int enable)
*/
void arch_ftrace_update_code(int command)
{
+ set_kernel_text_rw();
ftrace_modify_all_code(command);
+ set_kernel_text_ro();
}
int __init ftrace_dyn_arch_init(void)
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..b071ce64d173 100644
--- a/arch/powerpc/mm/pgtable_32.c
+++ b/arch/powerpc/mm/pgtable_32.c
@@ -41,6 +41,7 @@ unsigned long ioremap_bot;
EXPORT_SYMBOL(ioremap_bot); /* aka VMALLOC_END */
extern char etext[], _stext[], _sinittext[], _einittext[];
+extern char __start_rodata[], __init_begin[];
__ref pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
{
@@ -375,6 +376,41 @@ void remap_init_ram(void)
change_page_attr(page, numpages, PAGE_KERNEL);
}
+#ifdef CONFIG_DEBUG_RODATA
+void set_kernel_text_rw(void)
+{
+ struct page *page = virt_to_page(_stext);
+ unsigned long numpages = PFN_UP((unsigned long)etext) -
+ PFN_DOWN((unsigned long)_stext);
+
+ change_page_attr(page, numpages, PAGE_KERNEL_X);
+}
+
+void set_kernel_text_ro(void)
+{
+ struct page *page = virt_to_page(_stext);
+ unsigned long numpages = PFN_UP((unsigned long)etext) -
+ PFN_DOWN((unsigned long)_stext);
+
+ change_page_attr(page, numpages, PAGE_KERNEL_ROX);
+}
+
+void mark_rodata_ro(void)
+{
+ /*
+ * mark .rodata as read only. Use __init_begin rather than __end_rodata
+ * to cover NOTES and EXCEPTION_TABLE.
+ */
+ struct page *page = virt_to_page(__start_rodata);
+ unsigned long numpages = PFN_UP((unsigned long)__init_begin) -
+ PFN_DOWN((unsigned long)__start_rodata);
+
+ set_kernel_text_ro();
+
+ 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
