[PATCH v2 3/3] powerpc/mm: Implement CONFIG_DEBUG_RODATA on PPC32
From: Christophe Leroy <hidden>
Date: 2017-04-21 13:02:29
Also in:
lkml
Subsystem:
function hooks (ftrace), linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Steven Rostedt, Masami Hiramatsu, Madhavan Srinivasan, Michael Ellerman, Linus Torvalds
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 <redacted> --- v2: For ftrace, only change the attributes of the page to be modified arch/powerpc/Kconfig.debug | 11 +++++++++++ arch/powerpc/include/asm/pgtable.h | 8 ++++++++ arch/powerpc/kernel/ftrace.c | 8 +++++--- arch/powerpc/mm/init_32.c | 3 ++- arch/powerpc/mm/pgtable_32.c | 36 ++++++++++++++++++++++++++++++++++++ 5 files changed, 62 insertions(+), 4 deletions(-)
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/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 32509de6ce4c..06d2ac53f471 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c@@ -46,6 +46,7 @@ static int ftrace_modify_code(unsigned long ip, unsigned int old, unsigned int new) { unsigned int replaced; + int err; /* * Note:
@@ -67,10 +68,11 @@ ftrace_modify_code(unsigned long ip, unsigned int old, unsigned int new) } /* replace the text with the new text */ - if (patch_instruction((unsigned int *)ip, new)) - return -EPERM; + set_kernel_text_rw(ip); + err = patch_instruction((unsigned int *)ip, new); + set_kernel_text_ro(ip); - return 0; + return err ? -EPERM : 0; } /*
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..972effec1bb2 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 +376,41 @@ void remap_init_ram(void) change_page_attr(page, numpages, PAGE_KERNEL); } +#ifdef CONFIG_DEBUG_RODATA +void set_kernel_text_rw(unsigned long addr) +{ + 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 (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); +} +#endif + #ifdef CONFIG_DEBUG_PAGEALLOC void __kernel_map_pages(struct page *page, int numpages, int enable) {
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2.12.0